What Is "adequate Protein"?

[Amazoniac]

From 'Nutrition for all the Women':

"Enzymes are continually being destroyed and synthesized in active tissues. When a vitamin binds to its enzyme, it helps to stabilize the enzyme against degradation, leading to a higher concentration of the enzyme. In the same way, the "substrate" of an enzyme (the material it changes chemically) can stabilize the enzyme."

"When we eat a diet that is very low in a particular nutrient, such as protein, we lose many of the enzymes involved in handling that nutrient. Without those enzymes, a meal rich in protein, for example, can liberate more ammonia than the body can dispose of, and the person can be poisoned. Many vegetarians have experienced this "toxic" effect of meat or cheese or milk, and so believe that "animals foods" can cause mental dullness. headaches, dizziness, etc. But for a meat eater, the same process can cause vegetables to produce gas, as slow carbohydrate digestion lets bacteria break them down. Changing to any new diet, or ending a fast, should be done gradually, allowing at least several days for enzyme adaptation. The same rule would probably apply to nutritional supplements. If gas is a problem even when change of diet isn't responsible, a thyroid deficiency should be considered. Lack of stomach acid is typical in hypothyroidism, but is only one aspect of a generalized digestive depression."

"A few years ago, most of the nutritional problems that I saw were caused by physicians, by refined convenience foods, and by poverty. Recently, most of the problems seem to be caused by badly designed vegetarian diets, or by acceptance of the idea that 40 grams of protein per day is sufficient. The liver and other organs deteriorate rapidly on low-protein diets. Observe the faces of the wheat-grass promoters, the millet-eaters, the "anti-mucus" dieters, and other low-protein people. Do they look old for their age?"​

 

[Amazoniac]

- Biochemical, Physiological, and Molecular Aspects of Human Nutrition (978-1-4377-0959-9)

"The Food and Agriculture Organization, World Health Organization, and United Nations University (FAO/WHO/UNU, 2007) define a “safe” daily intake of dietary protein as 0.83 g high-quality protein per kg body weight, or 58 g/day for the reference 70-kg man and 47 g/day for the reference 57-kg woman. The approximate median intake of protein for adults aged 31 to 50 years in the United States is 100 g/day for men and 65 g/day for women. In addition to food proteins, the body digests 50 to 100 g per day of endogenous protein that is secreted into or sloughed into the lumen of the gastrointestinal tract. These endogenous proteins include proteins in saliva, gastric juice, and other secretions; pancreatic enzymes; mucoproteins; sloughed intestinal cells; and proteins that leak into the intestinal lumen from the blood. Most of this mixture of exogenous and endogenous proteins (115 to 200 g/day) is efficiently digested and taken up by the absorptive enterocytes as free amino acids and dipeptides and tripeptides. Around 85% of the total protein is absorbed anterior to the end of the small intestine (terminal ileum), with around 10 to 20 g of protein entering the colon each day. Daily fecal nitrogen losses amount to the equivalent of about 10 g of protein."​

 

[MetabolicTrash]

The high protein intake contrasts with the idea of being carb-driven though in way that it promotes possible fat gain (i.e., getting more protein means getting much more carbs, which has a sum of more overall calories needed). In order to get a lot of protein but also a relatively high carb:protein ratio, you'd need to consistently eat a high-ish amount of calories (or at least 2,500+ minimum) for the most part. I can't imagine someone getting, say, 100+ grams of protein but also then wanting 3-4+x the carbs, making that 300-400+ grams of carbs a day on top of all that protein and not even including fats yet. Also, the higher the protein intake (and if you're not adding in pure collagen/gelatin) then it becomes much more stressful to get all of that protein from fewer limited/constrained sources -- or having to find new and (possibly bad) sources, like more PUFA and etc. I know some people here talk about how easy it is to hit 300-400+ grams of carbs and 100+ of protein, but that's only if you're eating the exact same things at high amounts (tons of OJ, of course, can give you plenty of B vitamins and carbs -- but is everyone really going to down multiple quarts or more of this every single day?). The same problem with protein -- barring gelatin and such, it's tough to also be anti-iron/PUFA/mercurcy/etc. but also suggesting tons of fish/meat to meet protein demands, while then having to worry also about upping carbs relative to the protein by 3x or more (basically the more protein you're scavenging for, your carb needs are expected to have to go up significantly as well).

The problem with consistently getting in this amount of calories for me would be getting higher bodyfat slowly, which is why I don't follow the "get more calories" advice aimlessly, even if "Peat-friendly." I'm not just going to set some high number and eat that much mindlessly 24/7 -- I believe it needs to be gradual and/or in strides since I come from low-calorie diets and do not want to suddenly go high calories.

I can't speak for others, but I personally (and others likely) also can't stomach just doing nothing but drinking quarts of milk and OJ all day, every day and never mixing it up for way of getting adequate protein and carbs and some vitamins/etc. I try and limit red meat and such, but it becomes tough getting ~80 grams of protein minimum consistently without reaching out to the more "bad stuff" every now and then (before I would get 100+ easily before Peat because endless nuts/meats/PUFA protein shakes/beans/etc.). I also can't always rely upon having all ideal foods available at all times either, which can be a cost burden (cheese can be expensive, as can lots of gelatin + oysters + organ meats).

Though today I would have to admit that I've been pretty thirsty and craving lots of orange juice, but most days I'm not quite feeling like drinking 6-8 cups of it or milk.

 

[Cirion]

In my experience, protein has a sharp upside down U curve where too much is disasterous to me but so is too little. My best days are in the range of 70-80g protein or so. Keeping in mind that of that 70-80g, some may be in the form of potato, which actually has more protein than at face value due to keto-acids, so the real range for me may be like 70-100 gram. The tricky thing for me is that I'm sensitive also to too much cysteine and tryptophan, which means I need a good amount of protein in the form of gelatin to avoid those AA's.

 

[ExCarniv]

The high protein intake contrasts with the idea of being carb-driven though in way that it promotes possible fat gain (i.e., getting more protein means getting much more carbs, which has a sum of more overall calories needed). In order to get a lot of protein but also a relatively high carb:protein ratio, you'd need to consistently eat a high-ish amount of calories (or at least 2,500+ minimum) for the most part. I can't imagine someone getting, say, 100+ grams of protein but also then wanting 3-4+x the carbs, making that 300-400+ grams of carbs a day on top of all that protein and not even including fats yet. Also, the higher the protein intake (and if you're not adding in pure collagen/gelatin) then it becomes much more stressful to get all of that protein from fewer limited/constrained sources -- or having to find new and (possibly bad) sources, like more PUFA and etc. I know some people here talk about how easy it is to hit 300-400+ grams of carbs and 100+ of protein, but that's only if you're eating the exact same things at high amounts (tons of OJ, of course, can give you plenty of B vitamins and carbs -- but is everyone really going to down multiple quarts or more of this every single day?). The same problem with protein -- barring gelatin and such, it's tough to also be anti-iron/PUFA/mercurcy/etc. but also suggesting tons of fish/meat to meet protein demands, while then having to worry also about upping carbs relative to the protein by 3x or more (basically the more protein you're scavenging for, your carb needs are expected to have to go up significantly as well).

The problem with consistently getting in this amount of calories for me would be getting higher bodyfat slowly, which is why I don't follow the "get more calories" advice aimlessly, even if "Peat-friendly." I'm not just going to set some high number and eat that much mindlessly 24/7 -- I believe it needs to be gradual and/or in strides since I come from low-calorie diets and do not want to suddenly go high calories.

I can't speak for others, but I personally (and others likely) also can't stomach just doing nothing but drinking quarts of milk and OJ all day, every day and never mixing it up for way of getting adequate protein and carbs and some vitamins/etc. I try and limit red meat and such, but it becomes tough getting ~80 grams of protein minimum consistently without reaching out to the more "bad stuff" every now and then (before I would get 100+ easily before Peat because endless nuts/meats/PUFA protein shakes/beans/etc.). I also can't always rely upon having all ideal foods available at all times either, which can be a cost burden (cheese can be expensive, as can lots of gelatin + oysters + organ meats).

Though today I would have to admit that I've been pretty thirsty and craving lots of orange juice, but most days I'm not quite feeling like drinking 6-8 cups of it or milk.

Nothing wrong with eating 150-200g of meat everyday, gelatin and 2 eggs, (with meat) you're eating complete AAs when you pairing it with gelatin, plus lots of other nutrients, specially Niacin, Potassium and Selenium.

I tried high P and low P diets and both were terrible, I found a sweet spot around 120g, as male, and pretty active.

 

[Jennifer]

The high protein intake contrasts with the idea of being carb-driven though in way that it promotes possible fat gain (i.e., getting more protein means getting much more carbs, which has a sum of more overall calories needed). In order to get a lot of protein but also a relatively high carb:protein ratio, you'd need to consistently eat a high-ish amount of calories (or at least 2,500+ minimum) for the most part. I can't imagine someone getting, say, 100+ grams of protein but also then wanting 3-4+x the carbs, making that 300-400+ grams of carbs a day on top of all that protein and not even including fats yet. Also, the higher the protein intake (and if you're not adding in pure collagen/gelatin) then it becomes much more stressful to get all of that protein from fewer limited/constrained sources -- or having to find new and (possibly bad) sources, like more PUFA and etc. I know some people here talk about how easy it is to hit 300-400+ grams of carbs and 100+ of protein, but that's only if you're eating the exact same things at high amounts (tons of OJ, of course, can give you plenty of B vitamins and carbs -- but is everyone really going to down multiple quarts or more of this every single day?). The same problem with protein -- barring gelatin and such, it's tough to also be anti-iron/PUFA/mercurcy/etc. but also suggesting tons of fish/meat to meet protein demands, while then having to worry also about upping carbs relative to the protein by 3x or more (basically the more protein you're scavenging for, your carb needs are expected to have to go up significantly as well).

Not that anyone but me would want to eat this way or should eat this, it is possible. I easily get 100g of protein and 400g of carbs (from whole fruit, and to a much lesser extent, Thai coconut water, fruit juice, fruit molasses, maple syrup and honey) before I even hit 2000 calories — I eat roughly 2500 a day. I don't crave much fat other than the occasional young coconut meat, olives or avocado so my PUFA intake averages 2g or less a day. I get my animal protein from shellfish, lean meat and occasionally eggs and despite this, I'm taking in less phosphorus and inflammatory amino acids than I was when I was consuming a diet of dairy and fruit. I get the majority of my calcium from a concentrated herbal infusion I make from nettles and horsetail, and this leaves me with an average calcium to phosphorus ratio of 1:1–2:1. I get blood work done every few months and my latest iron and heavy metals (including mercury) panels came back normal.

 

[MetabolicTrash]

Not that anyone but me would want to eat this way or should eat this, it is possible. I easily get 100g of protein and 400g of carbs (from whole fruit, and to a much lesser extent, Thai coconut water, fruit juice, fruit molasses, maple syrup and honey) before I even hit 2000 calories — I eat roughly 2500 a day. I don't crave much fat other than the occasional young coconut meat, olives or avocado so my PUFA intake averages 2g or less a day. I get my animal protein from shellfish, lean meat and occasionally eggs and despite this, I'm taking in less phosphorus and inflammatory amino acids than I was when I was consuming a diet of dairy and fruit. I get the majority of my calcium from a concentrated herbal infusion I make from nettles and horsetail, and this leaves me with an average calcium to phosphorus ratio of 1:1–2:1. I get blood work done every few months and my latest iron and heavy metals (including mercury) panels came back normal.

Yeah, I realized my post is a bit off a while after. It's obviously possible to hit all of those macros without going too overboard on calories.

My problem would be finding adequate food in general that can get me the most nutrients without any empty/extra calories, which can be problematic since I sometimes have to settle for the PUFA stuff at times, even if low amounts (< 10g still mostly, but > 5 usually on those days).

Also, beware of eggs sometimes as I've noticed that most eggs I find in stores that are large have around 1 or maybe 2 grams of PUFAs, even though they have lots of good stuff despite this. I tend to avoid eggs because of this, but not sure if cooking them in coconut oil or something could mitigate it. That may sound fairly low, but I would need to keep PUFAs low in general/look out for them because of some foods I end up eating sometimes might have it and I don't want to double up on it or such.

 

[tallglass13]

Does anybody ever use a scale to weigh their protein. I use one, and I easily get 100g from beef, and that is only like 6 oz., from very lean Filet of Mignon. But there must be consideration for water content and fat. I have a suspicion that people may be getting way too much protein if you are not using a scale. You will find that when using a food scale, its fairly easy to hit 100g.

 

[ExCarniv]

Yeah, I realized my post is a bit off a while after. It's obviously possible to hit all of those macros without going too overboard on calories.

My problem would be finding adequate food in general that can get me the most nutrients without any empty/extra calories, which can be problematic since I sometimes have to settle for the PUFA stuff at times, even if low amounts (< 10g still mostly, but > 5 usually on those days).

Also, beware of eggs sometimes as I've noticed that most eggs I find in stores that are large have around 1 or maybe 2 grams of PUFAs, even though they have lots of good stuff despite this. I tend to avoid eggs because of this, but not sure if cooking them in coconut oil or something could mitigate it. That may sound fairly low, but I would need to keep PUFAs low in general/look out for them because of some foods I end up eating sometimes might have it and I don't want to double up on it or such.

Eggs from chickens raised on pastures, the Vit E content is almost three times more than regular eggs from chicken soy fed.

So it could be possible that good quality eggs with high amounts of Vitamin E, could mitigate the pufa content, one or two a day wouldn't do too much harm, Peat says if eggs are from pasture raised chicken, they are ok to eat everyday, with regular eggs he said better to avoid or eat one per week.

 

[Cirion]

Does anybody ever use a scale to weigh their protein. I use one, and I easily get 100g from beef, and that is only like 6 oz., from very lean Filet of Mignon. But there must be consideration for water content and fat. I have a suspicion that people may be getting way too much protein if you are not using a scale. You will find that when using a food scale, its fairly easy to hit 100g.

How do you mean? 4 oz of lean meat is roughly 20-24 gram of protein. It's not a 1:1 translation. 100 gram of chicken or beef or whatever does not equate to 100 gram of protein usable by the body. Most protein is horribly inefficiently processed by the body. Haidut made a post on this. Some proteins may have 85% waste and only 15% actually utilized.

 

[Jennifer]

That may sound fairly low, but I would need to keep PUFAs low in general/look out for them because of some foods I end up eating sometimes might have it and I don't want to double up on it or such.

Yeah, that makes sense. I eat such little fat that an egg doesn't put me over, but I can understand how it would for you. I also get my eggs from a local biodynamic farm that raises their hens on pasture so as ExCarniv pointed out, their nutritional profile may be different than conventional eggs. If you stick to lean proteins and low-fat carb sources, you still get that much PUFA?

Does anybody ever use a scale to weigh their protein. I use one, and I easily get 100g from beef, and that is only like 6 oz., from very lean Filet of Mignon. But there must be consideration for water content and fat. I have a suspicion that people may be getting way too much protein if you are not using a scale. You will find that when using a food scale, its fairly easy to hit 100g.

When I first reintroduced meat back into my diet, I weighed it before and after cooking it to get a more accurate idea of what I was getting for protein and logged it in crono as cooked weight. I typically go by cravings and will usually end up around the same amount daily, except for days leading up to my period when my appetite skyrockets or when I'm more active than usual.

How do you mean? 4 oz of lean meat is roughly 20-24 gram of protein. It's not a 1:1 translation. 100 gram of chicken or beef or whatever does not equate to 100 gram of protein usable by the body. Most protein is horribly inefficiently processed by the body. Haidut made a post on this. Some proteins may have 85% waste and only 15% actually utilized.

So would that mean we also aren't utilizing as much of the inflammatory AAs as the more bioavailable proteins — I can't remember but I think whey, eggs and milk are the most bioavailable? I didn't see potato or mushroom protein listed on charts the last time I looked.

 

[tara]

I use one, and I easily get 100g from beef, and that is only like 6 oz., from very lean Filet of Mignon. But there must be consideration for water content and fat.

I would expect 6oz lean beef filet mignon to give ~ 50g protein (or less protein if it is more fat) eg Beef, tenderloin, separable lean and fat, trimmed to 0" fat, all grades, cooked, broiled [Beef Medallions, Filet Mignon] Nutrition Facts & Calories.
But there's at least a bit of protein in most foods, so you might be getting plenty in the day anyway.

 

[MetabolicTrash]

Yeah, that makes sense. I eat such little fat that an egg doesn't put me over, but I can understand how it would for you. I also get my eggs from a local biodynamic farm that raises their hens on pasture so as ExCarniv pointed out, their nutritional profile may be different than conventional eggs. If you stick to lean proteins and low-fat carb sources, you still get that much PUFA?

Well no. If I eat everything lean then PUFA would be nearly zero or as you said. The problem is that I try to avoid too much red meat too often, which then makes it difficult to hit the protein macros. If I ate like tuna, chicken or etc. it would be super easy to get enough protein without PUFA much, but that would require significant meat eating every day.

 

[Cirion]

Well no. If I eat everything lean then PUFA would be nearly zero or as you said. The problem is that I try to avoid too much red meat too often, which then makes it difficult to hit the protein macros. If I ate like tuna, chicken or etc. it would be super easy to get enough protein without PUFA much, but that would require significant meat eating every day.

Your struggles sound slightly different to mine yet similar. I also find that I don't like to eat much meat maybe for slightly different reasons than you perhaps, but the effect is the same, I find it hard to get enough protein while eating little or even no meat. I have found that even 8 oz every day is too much. Was just reading in Vani Hari's "Food babe" book that she found she doesn't like to eat more than 8 oz a WEEK! Crazy. I'm thinking of halving my intake again and seeing how that goes (just 4 oz a day). I figure as long as you do that, as well as get ample gelatin, and ample vegetable proteins, it *should* be enough (get me to my 70-80g minimum intake). 4 oz of meat should be low enough to avoid the problems that can come from animal protein (cystine, tryptophan, potential hormones... etc)

 

[tallglass13]

How do you mean? 4 oz of lean meat is roughly 20-24 gram of protein. It's not a 1:1 translation. 100 gram of chicken or beef or whatever does not equate to 100 gram of protein usable by the body. Most protein is horribly inefficiently processed by the body. Haidut made a post on this. Some proteins may have 85% waste and only 15% actually utilized.

I said 6 oz though, but last night I weighed my Filet, its Center Cut high quality, it was 9 0z and 80g of Protein. After the beef, I wouldn't need much more, I then have some Raw skimmed milk at 12 grams every cup. Im trying to lose a bit of weight, so I don't want extra fat gain from too much protein. I learned that beef is of high quality, and I thought is was very usable for Protein for the body. Egg of course is hard to measure because of the yolk fat and lots of water. However, my only point is weight of protein is the grams needed by the body, obviously, but I don't think people think of it that way, and only look at numbers on packaging of products.

 

[Jennifer]

Well no. If I eat everything lean then PUFA would be nearly zero or as you said. The problem is that I try to avoid too much red meat too often, which then makes it difficult to hit the protein macros. If I ate like tuna, chicken or etc. it would be super easy to get enough protein without PUFA much, but that would require significant meat eating every day.

Oh, okay. Gotcha. I wasn't sure if your fat was coming from protein sources alone or also coconut oil, butter, tallow etc. Do you react poorly to meat or are you wanting to avoid it solely for the reasons you mentioned a few posts back? If it's the latter, have you ever compared protein sources on cronometer or other similar food databases based on the same amount of protein for each source?

A while back, I logged 100g worth of protein for each of the foods I was comparing and found that the inflammatory AA totals were so similar among all of them and if one food was higher in an inflammatory AA, it was typically lower in at least one of the other ones. I thought in terms of the inflammatory AAs that potatoes, mushrooms and greens would have a better profile than milk, scallops, chicken breast, lean beef and low-fat tofu, but I discovered they don't and all but the milk have a higher glycine content than they do, especially the scallops. The scallops have almost 3x the amount, which made me wonder if it's one of the reasons why, along with crab, I tolerate it the best out of all the higher protein sources I've tried.

 

[Cirion]

I said 6 oz though, but last night I weighed my Filet, its Center Cut high quality, it was 9 0z and 80g of Protein. After the beef, I wouldn't need much more, I then have some Raw skimmed milk at 12 grams every cup. Im trying to lose a bit of weight, so I don't want extra fat gain from too much protein. I learned that beef is of high quality, and I thought is was very usable for Protein for the body. Egg of course is hard to measure because of the yolk fat and lots of water. However, my only point is weight of protein is the grams needed by the body, obviously, but I don't think people think of it that way, and only look at numbers on packaging of products.

I don't find that protein directly increases fat gain. That said, I do find that excess protein can increase inflammation from cysteine, tryptophan etc, so in that sense it does indirectly increase fat gain for me. Fatty protein though like eggs or fatty cuts of beef could easily send you over the edge if you're like me and get fat easily from dietary fats.

Beef is one of the safer meats definitely, its low in tryptophan compared to most other proteins. I still prefer organ meats though over muscle meats, personally. If I'm gonna limit my meat to only 4 oz a day, better believe I'm gonna maximize the nutrition as a result (Beef liverwurst has 5x the B12 content of regular muscle meat beef for example, quite the powerhouse of nutrition). so even just 4 oz of liverwurst puts me at like 600% RDA of B12.

 

[Amazoniac]

Dietary protein intake and human health

Copied and pasted without criteria:

"The English word protein originated from the Greek “proteios”, meaning prime or primary. This term is very appropriate in nutrition, because protein is the most fundamental component of tissues in animals and humans.2 Dietary protein has no nutritional value unless it is hydrolyzed by proteases and peptidases to AA, dipeptides, or tripeptides in the lumen of the small intestine (Fig. 1). Thus, the content, digestibility coefficients, and relative proportions of AA in dietary protein are the determinants of its nutritional value.3"

"AA provide nitrogen, hydrocarbon skeletons, and sulfur (essential components of organisms), and cannot be replaced by any other nutrients (including carbohydrate and lipids) because neither nitrogen nor sulfur is made in the body. AA are essential precursors for the synthesis of proteins, peptides, and low-molecular weight substances (e.g., glutathione, creatine, nitric oxide, dopamine, serotonin, RNA and DNA) with enormous physiological importance.4,5 Dietary glutamate, glutamine and aspartate are major metabolic fuels for the mammalian small intestine in the fed state, whereas glutamine in the arterial blood is almost the exclusive source of energy for this organ in the post-absorptive state.2 [¿] In addition, glutamine provides ∼50% and 35% of ATP in lymphocytes and macrophages, respectively, to sustain immune responses.6 [?]"

"Thus, AA are essential for the health, growth, development, reproduction, lactation, and survival of organisms. This is graphically indicated by metabolic disorders, kwashiorkor (caused by a severe deficiency of protein) and marasmus (caused by the severe deficiency of both protein and energy) in humans, particularly in many children of developing nations.7 Less severe forms of dietary protein deficiency occur in elderly subjects (e.g., the home-bound elderly), including those in developed countries, thereby increasing their susceptibility to metabolic and infectious diseases.8 The other end of the nutrition spectrum is the overconsumption of dietary AA and protein from meals and excessive supplementation, which can also compromise the health of humans, particularly those with hepatic or renal dysfunction.9"

"A free-living person eats what he/she likes. However, it is scientifically relevant to ask how much dietary protein or AA a human being needs to fulfill his/her physiological needs and prevent or ameliorate a catabolic state (e.g., sarcopenia in adults). There is a rich history of this research subject over the past two centuries, but it is also a source of continuing debate and disagreement among the investigators.1,11,13–15 Based on the amounts of protein consumed by a group of German workmen doing moderate physical work, von Liebig estimated in 1840 that the average adult would require a dietary intake of 120 g protein per day.16 Extrapolating results from canine studies, von Voit suggested in 1881 a dietary intake of 118 g protein per day for the average adult.17 In 1902, Atwater recommended a dietary intake of 125 g protein per day for the average adult, because he thought that U.S. workmen generally worked harder than Germans.18 However, Chittenden challenged these values of protein intake in 1904, based on his observations that: (a) adults remained healthy and in N balance for six months on daily diets containing 61 to 62 g protein; and (b) college student athletes consuming 64 g protein per day maintained their levels of athletic performance and well-being.19"

"[..]excessive amounts of AA are generally not stored in the body and will be disposed of primarily via oxidation and urea synthesis in humans. An increase in the oxidation of an AA is usually an indicator of its excessive availability in the body, provided that there are no significant changes in the concentrations of regulatory hormones coenzymes, cofactors, or metabolites.21 In other words, if the supply of an AA exceeds its needs by the human, this AA is oxidized to CO2, water, ammonia, and urea (Fig. 2)."

"Each method for determining the dietary requirements of AA and protein has its own strengths and weaknesses. N balance measurement is a simple and relatively inexpensive approach to estimate the dietary requirements of AA and proteins by humans. The common advantages of both the direct and the indicator AA oxidation methods over the N balance technique are that: (a) the dietary requirements of AA can be estimated within a short period of time after several days of adaptation to experimental diets, without the need for a long, expensive stay (e.g., one week or longer) in a metabolic facility; and (b) changes in whole-body oxidation of a specific AA in response to different intakes of dietary AA or protein can be assessed. However, both N balance and isotope studies are only short-term experiments, and do not take, into consideration, the functional needs of AA beyond protein synthesis in humans."

"Let us use histidine and arginine as examples to illustrate some shortcomings of N balance studies. The results of the N balance studies by Rose did not reveal the dietary requirements of histidine or arginine by healthy adults.10 Explanations for the failure to identify histidine as an EAA are that: (a) hemoglobin contains a relatively large amount of histidine and breakdown of this protein yields histidine; and (b) skeletal muscle contains millimolar concentrations of histidine in the form of dipeptides (e.g., carnosine) and their hydrolysis provides histidine. Extending the experimental period of feeding a histidine-free diet from 8 to 28 days or longer substantially reduces the endogenous release of histidine from hemoglobin and intramuscular small peptides, thereby resulting in a negative N balance in adults.24,25 On the other hand, arginine was traditionally not considered as an EAA for healthy adults.26 However, feeding an arginine-deficient diet to adult men for 9 days decreased both the number and motility of sperm cells by 90% despite N balance at equilibrium.27 This striking observation underlines a critical role for arginine in spermatogenesis. In addition, extensive studies with pregnant dams have shown that dietary arginine is required for the optimal survival and growth of embryos and fetuses.28 These findings argue strongly that functional needs beyond protein synthesis and N balance should be important criteria for the dietary requirements of AA and proteins. Despite its shortcomings, the N balance approach remains an invaluable procedure for determining the dietary requirements of AA and proteins for humans."

"The use of AA as major metabolic fuels for tissues other than the small intestine and immune cells is not desirable because of their lower energetic efficiency, as compared with fatty acids and glucose.1 In addition, catabolism of many AA requires NADPH, which is generated primarily from glucose metabolism via the pentose cycle."

"There is often confusion about either the energy value of protein or dietary protein intake as a percentage of energy intake in human nutrition. The gross calories of fat, protein, and starch, as determined in bomb combustion, are 9.4, 5.4, and 4.1 kcal g−1, respectively. The amounts of energy released from the oxidation of fat, protein, and starch to water and CO2 in vivo are 9.4, 4.1, and 4.1 kcal g−1, respectively. Because not all dietary fat, protein, and starch are digested in stomach and the small intestine, and because protein oxidation in the body is incomplete, the physiological values of energy in dietary fat, protein, and starch for humans are usually taken to be 9, 4, and 4 kcal g−1, respectively."

"The dietary requirements of AA and protein are affected by: (a) dietary factors (e.g., AA content and proportions, energy intake, presence or absence of other substances, and food processing); (b) physiological characteristics of subjects (e.g., age, sex, genetic backgrounds, circadian clock, hormones, pregnancy, lactation, and physical activity); (c) pathological states (e.g., infection, trauma, neoplasia, diabetes, obesity, cardiovascular disease, and fetal growth restriction); and (d) environmental factors (e.g., temperatures, toxic agents, air pollution, dietary habits, sanitation, and personal hygiene). These factors should be taken into consideration in estimating the human requirements for dietary AA.30–32"

"Based on the meta-analysis of short-term N balance studies in humans,33 the Recommended Dietary Allowance (RDA) of protein for a healthy adult with minimal physical activity is currently 0.8 g protein per kg BW per day (Table 1). For comparison, values for infants and children are greater because they grow and gain protein. Dietary protein is assumed to be of high quality (a typical mixture of animal- and plant-source proteins) with a biological value of 75% (efficiency with which a truly digestible protein is utilized for maintenance and protein deposition in the body). Values on percentages of dietary energy from proteins (e.g., dietary protein contributing to 10 to 35% of total dietary energy; e.g., 120 kJ per kg BW per day for 31- to 50-year-old men with minimal physical activity) should not be used out of context without the consideration of total daily caloric intake. These data translate into 0.75 to 2.63 g protein per kg BW per day for a healthy adult who has minimum physical activity. As suggested previously,34 functional needs (e.g., support of spermatogenesis, fetal survival and growth, blood circulation, resistance to infectious disease, as well as skeletal muscle mass and health) should also be an important criterion to recommend dietary AA and protein requirements for humans. There are reports that consumption of 25 to 30 g high-quality protein (0.333 to 0.40 g per kg BW) and adequate energy in a single meal maximally stimulates skeletal-muscle protein synthesis in the resting 75 kg young adult man.35,36 This translates to 75 to 90 g protein for a 25–30 g of protein per meal for 3 meals daily (1.0 to 1.2 g per kg BW per day). Of note, an increase in skeletal-muscle protein synthesis occurs within 1–2 h after consumption of dietary protein or AA and is sustained for 3 h thereafter.37,38"

"Recent studies have shown that the N balance-based estimates of dietary AA requirements by humans are considerably lower than the values obtained by the AA oxidation methods. The differences can be up to 2- to 3-fold for many EAA (Table 2). These discrepancies may result from both methodological and physiological factors. In all the various versions of recommended AA requirements, only EAA are considered and represent only 8–27% of the RDA. This is clearly a limitation, as synthesizable AA are more abundant than EAA in tissues (e.g., skeletal muscle) [?] and can limit protein synthesis in skeletal muscles.39–41 The original N balance experiments may overestimate N retention due to methodological reasons, therefore underestimating dietary AA requirements. On the other hand, the use of tracers in metabolic research has potential problems associated with label dilution, isotope exchange, determination of intracellular specific activities of immediate precursors, and isotopic steady states.1 New knowledge about AA biochemistry and nutrition, as well as improved methodologies for studying whole-body AA metabolism, will be necessary to resolve the current dispute on the dietary requirement of AA by humans. Additionally, considerations should be given to dietary requirements of synthesizable AA.41"

"The RDA represents only minimum daily average dietary intake that meets the nutrient requirements of nearly all (97.5%) healthy individuals in a particular life stage.26 As noted previously, the RDA of a protein was recommended to meet N balance, and should not be considered as the optimal amount for maintenance, optimal health or specific functions of organs. In this regard, it is noteworthy that skeletal muscle is the major reservoir of AA in the body and undergoes decreases in both mass and physical strength with aging. Several lines of evidence show that the current RDA of protein is insufficient for adult humans with minimum physical activity. First, elderly adults who consumed diets providing 0.8 g protein per kg BW per day for 14 weeks lost skeletal-muscle mass.43 Second, men and women (70–79 years of age) lost the most amount of skeletal muscle during a 3-year period when they consumed the lowest amount of dietary protein (≤0.8 g protein per kg BW per day).44 Third, increasing dietary protein intake moderately above the RDA by 25–35% enhanced muscle protein anabolism and reduced the progressive loss of muscle weight in adults with advanced age.43–45 Thus, adequate protein intake is highly beneficial for healthy aging."

"A sedentary lifestyle has a profound negative effect on skeletal muscle. For example, a 7-day bed rest in young healthy males can decrease leg muscle mass by 3% and muscle O2 consumption by 4%.46 Much evidence shows that moderate exercise is beneficial for improving skeletal muscle mass as well as muscle and whole-body health, while reducing the risk of metabolic syndrome.32 Of interest, improvement in the sensitivity of myofibrillar protein synthesis to AA supply can persist for up to 24 h after resistance exercise.47 Even in the elderly, resistance exercise (e.g., weight-lifting) can enhance skeletal-muscle mass and strength.48 Indeed, dietary protein and moderate exercise have synergistic effects on skeletal-muscle protein synthesis. Thus, American College of Sports Medicine (ACSM) has recommended strength training for the elderly to sustain muscle mass and function.49"

"During exercise, there is a negative balance between the rates of protein synthesis and breakdown in the whole body, as well as an increase in the rate of whole-body AA oxidation, resulting in a transient catabolic state.50,51 The underlying mechanisms differ with the type of exercise in that exhaustive endurance exercise reduces the rate of protein synthesis without affecting protein breakdown in the whole body (including skeletal muscle).52 In contrast, a prolonged bout of resistance exercise results in an increase in the rate of protein breakdown in the whole body (including skeletal muscle) being greater than an increase in the rate of protein synthesis.52 The magnitudes of these changes also depend on the type of exercise. Even moderate exercise (e.g., 1 h treadmill exercise at 55% of VO2 max) stimulates whole-body protein catabolism by 25% in a healthy adult.53 This translates into the dietary protein requirement of ≥1 g per kg BW per day. Unless sufficient dietary protein is consumed during recovery for increased synthesis of muscle proteins, protein degradation will exceed protein synthesis, resulting in a loss of muscle mass and negative N balance. In support of this view, healthy adults who performed intensive exercise daily (9.9 kcal min−1 for 6 of 20 min periods) for 3 weeks and consumed 1 g protein per kg BW per day exhibited negative N balance during each day of the training program.51"

"Timing of protein or AA consumption is important for muscle recovery after exercise. Skeletal muscle takes up nutrients (e.g., AA, glucose and fatty acids) from the blood circulation most efficiently within the first 30–60 min after an exercise program is completed, followed by great reductions several hours later.32 Thus, the response of muscle protein synthesis to exercise-induced anabolism is much greater when AA intake is initiated immediately after the end of exercise, as compared to 3 h after the end of exercise.62 As noted previously, the proportions and amounts of all AA in diets should be considered when specific EAA are supplemented to subjects after exercise. For example, consuming individual branched-chain AA (BCAA) alone cannot enhance muscle protein synthesis when the availability of other AA is limited.63 This is because protein synthesis requires all 20 different AA as the building blocks."

"Through metabolites and cell signaling, AA play an important role in regulating the oxidation of fatty acids and glucose in a cell- and tissue-specific manner.5 For example, enzymes of metabolic pathways are synthesized from AA. Second, the physiological levels of NO (a product of arginine catabolism) enhance the oxidation of fatty acids and glucose to CO2 and water.64 Third, the physiological levels of glutathione (formed from cysteine, glycine and glutamate), taurine (a metabolite of methionine), glycine, proline, and hydroxyproline (derived from proline) protect cells and tissues from oxidative injury and inflammation.65 Fourth, thyroid hormones (derived from tyrosine) are required to maintain adequate rates of basal energy metabolism in humans.66 Fifth, creatine (formed from arginine, glycine, and methionine) is needed to store energy as phosphocreatine for muscular work and neurological function.67 Six, carnitine (synthesized from lysine, methionine and serine) is required to transport long-chain fatty acids from the cytoplasm into the mitochondrion for β-oxidation to yield acetyl-CoA.1 Seventh, serotonin and melatonin (metabolites of tryptophan) inhibit the production of inflammatory cytokines to maintain the health of adipose tissue, while regulating food intake and behavior by humans.39 Finally, arginine, leucine, glycine, tryptophan and glutamine activate the mTOR signaling pathway to stimulate skeletal-muscle protein synthesis,41 thereby partitioning dietary energy from the fat stores into muscle building."

"The rate of skeletal-muscle protein synthesis in healthy adults is 25% higher when protein intake is evenly distributed across breakfast, lunch, and dinner, compared with a pattern where most protein is consumed at the evening meal despite the same daily intake of total protein.72 This finding has important implications for improving skeletal-muscle mass, strength and function in older, physically active adults who generally experience a resistance to the stimuli of muscle protein synthesis and have a higher threshold of dietary protein intake to promote muscle protein synthesis."

"Of note, plants do not contain taurine or carnosine.1 Additionally, protein in animal products has a higher digestibility (∼95%) than proteins isolated from plants (∼85–92%) or proteins in whole plant foods (∼80–85%) which generally contain anti-nutritional factors.3"

"Several lines of evidence show that animal-source protein has a greater nutritional value than plant-source protein to sustain skeletal-muscle mass. First, dietary supplementation of 17.5 g milk protein per day during a 12-week resistance exercise program increased lean body mass (3.9 vs. 2.8 kg) than an isonitrogenous amount of soy protein.75 Second, compared with soy protein, dietary supplementation with 24 g whey per day to young men enhanced their lean tissue gains (3.3 vs. 1.8 kg) after 36 weeks of resistance exercise training.76 Third, ingestion of animal-source protein by healthy adults ranging from 17.5 to 40 g from whey, skimmed milk, or beef stimulated skeletal-muscle protein synthesis to a greater extent than the same amount of soy protein under resting and post-exercise conditions.61 Fourth, long-term vegetarianism resulted in reduced skeletal-muscle mass in older women, compared with consumption of an omnivorous diet (18.2 vs. 22.6 kg lean body mass).77 Thus, as a nutritional strategy, adequate consumption of animal protein (e.g., nutrient-dense lean meat) can reverse the decline in protein intake by adults in the age groups of ≥51 years. This simple means is vitally important for sustaining skeletal-muscle mass and improving health in aging adults."

"Globally, plant- and animal-based foods contribute ∼65% and 35% of protein, respectively, in human diets, and the opposite is true in North America.30"

"Protein deficiency causes multiple clinical syndromes,85 which are summarized in Table 4. This nutritional problem can occur in any community at any age due to illness or poor diets, and is frequently exacerbated by inadequate energy intake.22 Dietary protein deficiency not only contributes to poor growth, cardiovascular dysfunction, and high risk of infectious disease, but also exacerbates the deficiency of other nutrients (including vitamin A and iron) and worsens metabolic profiles (e.g., dyslipidemia and hyperglycemia) in humans. This is because of the need for protein to: (a) digest and absorb dietary nutrients by the small intestine; (b) transport nutrients (including long-chain fatty acids, vitamin A, and iron) and other molecules (e.g., cholesterol and triacylglycerols) in blood; and (c) oxidize nutrients (including fatty acids and glucose) to water and CO2.86–88"

"Safe (tolerable) upper limits for dietary protein intake (maximum safe intake) by young and adult humans have not been established, and can differ among individuals. Like any nutrient, divided protein intake at different meals of the day is preferred to reduce a sudden excess of any AA in the gastrointestinal tract, liver, brain, heart, kidneys, and other tissues. As noted previously, the Institute of Medicine recommended an acceptable macronutrient distribution range for protein intake at 10% to 35% of total energy for adults. It should be borne in mind that the dietary intake of energy should not exceed requirements and that the safety of protein intake is influenced by consumption of carbohydrates and lipids. In view of large variations among people in any age population, caution must be exercised not to adopt “one shoe fits all” guidelines when establishing safe upper limits of dietary protein intake by humans."

"Long-term consumption of any nutrients (including water, protein, and vitamin A) in high amounts may have adverse effects on human health.99 Protein intake greater than its safe upper limits in different age groups can exceed the ability of the liver, intestine, and kidneys to detoxify ammonia and should be avoided. Adverse effects of high protein intake include intestinal discomfort, hyperaminoacidemia, hyperammonemia, hyperinsulinemia, dehydration, irritation, nausea, diarrhea, liver and kidney injuries, fatigue, headache, seizures, high risk of cardiovascular disease, or even death.100 Problems of high protein intake can be exacerbated by low intake of carbohydrates because of additional burdens on the liver and kidney to produce large amounts of glucose from AA besides their roles in disposing of excessive ammonia and urea. Glucose is essential for meeting the energy requirements of the brain, red blood cells, renal medullar tissues, and retinal cells, and for the production of NADPH to support numerous biochemical (including anti-oxidative) reactions. Even during long-term starvation, the human brain still utilizes a large amount of glucose (i.e., 40% of the normal uptake of 125 g per day for a 70 kg person), and this glucose is derived primarily from AA."

"Efficient absorption of dietary minerals and mineralization depend on protein.108 In addition, protein is a major component of bones. Thus, adequate intake of protein, particularly from calcium- and phosphorus-rich milk products, is essential to support bone growth in infants and children and to sustain the mass and health of the skeleton in adults. There is a concern that high protein intake may stimulate urinary excretion of calcium, which may contribute to bone loss and subsequent development of osteopenia and osteoporosis.108 However, in free-living individuals, high protein intake is likely associated with high calcium intake, and, therefore, may compensate for a moderate increase, if any, in urinary excretion of calcium. Based on an extensive and systematic review of the literature, Sahni et al.109 concluded that dietary protein provided a significant benefit on bone health in humans. Likewise, there is evidence that adequate protein intake increases peak bone mass in both young and older adults.110,111 Thus, protein nutrition plays a key role in skeletal health to reduce risk for osteopenia and osteoporosis."

"In summary, adequate consumption of high-quality protein is essential for optimal growth, development, and health in humans. An appropriate mixture of animal- and plant-based foods is a practical way to ensure balanced provision of dietary AA for the young and the adult. There is not a fixed amount of protein intake that suits all the people in all age groups. Rather, individuals should adjust their intake of protein and other nutrients according to metabolic rates, physiological needs, and health status. A sufficient supply of both EAA and synthesizable AA (so-called nutritionally nonessential AA) plays a key role in sustaining skeletal-muscle protein synthesis, mass, and function (including physical strength), while improving insulin sensitivity, ameliorating ageing-associated sarcopenia, and reducing white-fat accretion. In practice, adequate consumption of lean meat (a source of not only high-quality dietary protein but also vitamins and minerals) can help individuals realize the health benefits of moderate or intense exercise. To date, there are myths about AA and protein nutrition in humans due to inadequate understanding of the science. Sufficient intake of high-quality protein from animal products (e.g., lean meat and milk) is essential for optimal growth, development, and health of children, as well as for optimal maintenance, function and health of tissues (including skeletal muscle, brain, heart, kidneys, liver and gut) in adults. However, consumption of protein above safe upper limits should be avoided to prevent any adverse health problems."​

 

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Copied and pasted without criteria:

"The English word protein originated from the Greek “proteios”, meaning prime or primary. This term is very appropriate in nutrition, because protein is the most fundamental component of tissues in animals and humans.2 Dietary protein has no nutritional value unless it is hydrolyzed by proteases and peptidases to AA, dipeptides, or tripeptides in the lumen of the small intestine (Fig. 1). Thus, the content, digestibility coefficients, and relative proportions of AA in dietary protein are the determinants of its nutritional value.3"

"AA provide nitrogen, hydrocarbon skeletons, and sulfur (essential components of organisms), and cannot be replaced by any other nutrients (including carbohydrate and lipids) because neither nitrogen nor sulfur is made in the body. AA are essential precursors for the synthesis of proteins, peptides, and low-molecular weight substances (e.g., glutathione, creatine, nitric oxide, dopamine, serotonin, RNA and DNA) with enormous physiological importance.4,5 Dietary glutamate, glutamine and aspartate are major metabolic fuels for the mammalian small intestine in the fed state, whereas glutamine in the arterial blood is almost the exclusive source of energy for this organ in the post-absorptive state.2 [¿] In addition, glutamine provides ∼50% and 35% of ATP in lymphocytes and macrophages, respectively, to sustain immune responses.6 [?]"

"Thus, AA are essential for the health, growth, development, reproduction, lactation, and survival of organisms. This is graphically indicated by metabolic disorders, kwashiorkor (caused by a severe deficiency of protein) and marasmus (caused by the severe deficiency of both protein and energy) in humans, particularly in many children of developing nations.7 Less severe forms of dietary protein deficiency occur in elderly subjects (e.g., the home-bound elderly), including those in developed countries, thereby increasing their susceptibility to metabolic and infectious diseases.8 The other end of the nutrition spectrum is the overconsumption of dietary AA and protein from meals and excessive supplementation, which can also compromise the health of humans, particularly those with hepatic or renal dysfunction.9"

"A free-living person eats what he/she likes. However, it is scientifically relevant to ask how much dietary protein or AA a human being needs to fulfill his/her physiological needs and prevent or ameliorate a catabolic state (e.g., sarcopenia in adults). There is a rich history of this research subject over the past two centuries, but it is also a source of continuing debate and disagreement among the investigators.1,11,13–15 Based on the amounts of protein consumed by a group of German workmen doing moderate physical work, von Liebig estimated in 1840 that the average adult would require a dietary intake of 120 g protein per day.16 Extrapolating results from canine studies, von Voit suggested in 1881 a dietary intake of 118 g protein per day for the average adult.17 In 1902, Atwater recommended a dietary intake of 125 g protein per day for the average adult, because he thought that U.S. workmen generally worked harder than Germans.18 However, Chittenden challenged these values of protein intake in 1904, based on his observations that: (a) adults remained healthy and in N balance for six months on daily diets containing 61 to 62 g protein; and (b) college student athletes consuming 64 g protein per day maintained their levels of athletic performance and well-being.19"

"[..]excessive amounts of AA are generally not stored in the body and will be disposed of primarily via oxidation and urea synthesis in humans. An increase in the oxidation of an AA is usually an indicator of its excessive availability in the body, provided that there are no significant changes in the concentrations of regulatory hormones coenzymes, cofactors, or metabolites.21 In other words, if the supply of an AA exceeds its needs by the human, this AA is oxidized to CO2, water, ammonia, and urea (Fig. 2)."

"Each method for determining the dietary requirements of AA and protein has its own strengths and weaknesses. N balance measurement is a simple and relatively inexpensive approach to estimate the dietary requirements of AA and proteins by humans. The common advantages of both the direct and the indicator AA oxidation methods over the N balance technique are that: (a) the dietary requirements of AA can be estimated within a short period of time after several days of adaptation to experimental diets, without the need for a long, expensive stay (e.g., one week or longer) in a metabolic facility; and (b) changes in whole-body oxidation of a specific AA in response to different intakes of dietary AA or protein can be assessed. However, both N balance and isotope studies are only short-term experiments, and do not take, into consideration, the functional needs of AA beyond protein synthesis in humans."

"Let us use histidine and arginine as examples to illustrate some shortcomings of N balance studies. The results of the N balance studies by Rose did not reveal the dietary requirements of histidine or arginine by healthy adults.10 Explanations for the failure to identify histidine as an EAA are that: (a) hemoglobin contains a relatively large amount of histidine and breakdown of this protein yields histidine; and (b) skeletal muscle contains millimolar concentrations of histidine in the form of dipeptides (e.g., carnosine) and their hydrolysis provides histidine. Extending the experimental period of feeding a histidine-free diet from 8 to 28 days or longer substantially reduces the endogenous release of histidine from hemoglobin and intramuscular small peptides, thereby resulting in a negative N balance in adults.24,25 On the other hand, arginine was traditionally not considered as an EAA for healthy adults.26 However, feeding an arginine-deficient diet to adult men for 9 days decreased both the number and motility of sperm cells by 90% despite N balance at equilibrium.27 This striking observation underlines a critical role for arginine in spermatogenesis. In addition, extensive studies with pregnant dams have shown that dietary arginine is required for the optimal survival and growth of embryos and fetuses.28 These findings argue strongly that functional needs beyond protein synthesis and N balance should be important criteria for the dietary requirements of AA and proteins. Despite its shortcomings, the N balance approach remains an invaluable procedure for determining the dietary requirements of AA and proteins for humans."

"The use of AA as major metabolic fuels for tissues other than the small intestine and immune cells is not desirable because of their lower energetic efficiency, as compared with fatty acids and glucose.1 In addition, catabolism of many AA requires NADPH, which is generated primarily from glucose metabolism via the pentose cycle."

"There is often confusion about either the energy value of protein or dietary protein intake as a percentage of energy intake in human nutrition. The gross calories of fat, protein, and starch, as determined in bomb combustion, are 9.4, 5.4, and 4.1 kcal g−1, respectively. The amounts of energy released from the oxidation of fat, protein, and starch to water and CO2 in vivo are 9.4, 4.1, and 4.1 kcal g−1, respectively. Because not all dietary fat, protein, and starch are digested in stomach and the small intestine, and because protein oxidation in the body is incomplete, the physiological values of energy in dietary fat, protein, and starch for humans are usually taken to be 9, 4, and 4 kcal g−1, respectively."

"The dietary requirements of AA and protein are affected by: (a) dietary factors (e.g., AA content and proportions, energy intake, presence or absence of other substances, and food processing); (b) physiological characteristics of subjects (e.g., age, sex, genetic backgrounds, circadian clock, hormones, pregnancy, lactation, and physical activity); (c) pathological states (e.g., infection, trauma, neoplasia, diabetes, obesity, cardiovascular disease, and fetal growth restriction); and (d) environmental factors (e.g., temperatures, toxic agents, air pollution, dietary habits, sanitation, and personal hygiene). These factors should be taken into consideration in estimating the human requirements for dietary AA.30–32"

"Based on the meta-analysis of short-term N balance studies in humans,33 the Recommended Dietary Allowance (RDA) of protein for a healthy adult with minimal physical activity is currently 0.8 g protein per kg BW per day (Table 1). For comparison, values for infants and children are greater because they grow and gain protein. Dietary protein is assumed to be of high quality (a typical mixture of animal- and plant-source proteins) with a biological value of 75% (efficiency with which a truly digestible protein is utilized for maintenance and protein deposition in the body). Values on percentages of dietary energy from proteins (e.g., dietary protein contributing to 10 to 35% of total dietary energy; e.g., 120 kJ per kg BW per day for 31- to 50-year-old men with minimal physical activity) should not be used out of context without the consideration of total daily caloric intake. These data translate into 0.75 to 2.63 g protein per kg BW per day for a healthy adult who has minimum physical activity. As suggested previously,34 functional needs (e.g., support of spermatogenesis, fetal survival and growth, blood circulation, resistance to infectious disease, as well as skeletal muscle mass and health) should also be an important criterion to recommend dietary AA and protein requirements for humans. There are reports that consumption of 25 to 30 g high-quality protein (0.333 to 0.40 g per kg BW) and adequate energy in a single meal maximally stimulates skeletal-muscle protein synthesis in the resting 75 kg young adult man.35,36 This translates to 75 to 90 g protein for a 25–30 g of protein per meal for 3 meals daily (1.0 to 1.2 g per kg BW per day). Of note, an increase in skeletal-muscle protein synthesis occurs within 1–2 h after consumption of dietary protein or AA and is sustained for 3 h thereafter.37,38"

"Recent studies have shown that the N balance-based estimates of dietary AA requirements by humans are considerably lower than the values obtained by the AA oxidation methods. The differences can be up to 2- to 3-fold for many EAA (Table 2). These discrepancies may result from both methodological and physiological factors. In all the various versions of recommended AA requirements, only EAA are considered and represent only 8–27% of the RDA. This is clearly a limitation, as synthesizable AA are more abundant than EAA in tissues (e.g., skeletal muscle) [?] and can limit protein synthesis in skeletal muscles.39–41 The original N balance experiments may overestimate N retention due to methodological reasons, therefore underestimating dietary AA requirements. On the other hand, the use of tracers in metabolic research has potential problems associated with label dilution, isotope exchange, determination of intracellular specific activities of immediate precursors, and isotopic steady states.1 New knowledge about AA biochemistry and nutrition, as well as improved methodologies for studying whole-body AA metabolism, will be necessary to resolve the current dispute on the dietary requirement of AA by humans. Additionally, considerations should be given to dietary requirements of synthesizable AA.41"

"The RDA represents only minimum daily average dietary intake that meets the nutrient requirements of nearly all (97.5%) healthy individuals in a particular life stage.26 As noted previously, the RDA of a protein was recommended to meet N balance, and should not be considered as the optimal amount for maintenance, optimal health or specific functions of organs. In this regard, it is noteworthy that skeletal muscle is the major reservoir of AA in the body and undergoes decreases in both mass and physical strength with aging. Several lines of evidence show that the current RDA of protein is insufficient for adult humans with minimum physical activity. First, elderly adults who consumed diets providing 0.8 g protein per kg BW per day for 14 weeks lost skeletal-muscle mass.43 Second, men and women (70–79 years of age) lost the most amount of skeletal muscle during a 3-year period when they consumed the lowest amount of dietary protein (≤0.8 g protein per kg BW per day).44 Third, increasing dietary protein intake moderately above the RDA by 25–35% enhanced muscle protein anabolism and reduced the progressive loss of muscle weight in adults with advanced age.43–45 Thus, adequate protein intake is highly beneficial for healthy aging."

"A sedentary lifestyle has a profound negative effect on skeletal muscle. For example, a 7-day bed rest in young healthy males can decrease leg muscle mass by 3% and muscle O2 consumption by 4%.46 Much evidence shows that moderate exercise is beneficial for improving skeletal muscle mass as well as muscle and whole-body health, while reducing the risk of metabolic syndrome.32 Of interest, improvement in the sensitivity of myofibrillar protein synthesis to AA supply can persist for up to 24 h after resistance exercise.47 Even in the elderly, resistance exercise (e.g., weight-lifting) can enhance skeletal-muscle mass and strength.48 Indeed, dietary protein and moderate exercise have synergistic effects on skeletal-muscle protein synthesis. Thus, American College of Sports Medicine (ACSM) has recommended strength training for the elderly to sustain muscle mass and function.49"

"During exercise, there is a negative balance between the rates of protein synthesis and breakdown in the whole body, as well as an increase in the rate of whole-body AA oxidation, resulting in a transient catabolic state.50,51 The underlying mechanisms differ with the type of exercise in that exhaustive endurance exercise reduces the rate of protein synthesis without affecting protein breakdown in the whole body (including skeletal muscle).52 In contrast, a prolonged bout of resistance exercise results in an increase in the rate of protein breakdown in the whole body (including skeletal muscle) being greater than an increase in the rate of protein synthesis.52 The magnitudes of these changes also depend on the type of exercise. Even moderate exercise (e.g., 1 h treadmill exercise at 55% of VO2 max) stimulates whole-body protein catabolism by 25% in a healthy adult.53 This translates into the dietary protein requirement of ≥1 g per kg BW per day. Unless sufficient dietary protein is consumed during recovery for increased synthesis of muscle proteins, protein degradation will exceed protein synthesis, resulting in a loss of muscle mass and negative N balance. In support of this view, healthy adults who performed intensive exercise daily (9.9 kcal min−1 for 6 of 20 min periods) for 3 weeks and consumed 1 g protein per kg BW per day exhibited negative N balance during each day of the training program.51"

"Timing of protein or AA consumption is important for muscle recovery after exercise. Skeletal muscle takes up nutrients (e.g., AA, glucose and fatty acids) from the blood circulation most efficiently within the first 30–60 min after an exercise program is completed, followed by great reductions several hours later.32 Thus, the response of muscle protein synthesis to exercise-induced anabolism is much greater when AA intake is initiated immediately after the end of exercise, as compared to 3 h after the end of exercise.62 As noted previously, the proportions and amounts of all AA in diets should be considered when specific EAA are supplemented to subjects after exercise. For example, consuming individual branched-chain AA (BCAA) alone cannot enhance muscle protein synthesis when the availability of other AA is limited.63 This is because protein synthesis requires all 20 different AA as the building blocks."

"Through metabolites and cell signaling, AA play an important role in regulating the oxidation of fatty acids and glucose in a cell- and tissue-specific manner.5 For example, enzymes of metabolic pathways are synthesized from AA. Second, the physiological levels of NO (a product of arginine catabolism) enhance the oxidation of fatty acids and glucose to CO2 and water.64 Third, the physiological levels of glutathione (formed from cysteine, glycine and glutamate), taurine (a metabolite of methionine), glycine, proline, and hydroxyproline (derived from proline) protect cells and tissues from oxidative injury and inflammation.65 Fourth, thyroid hormones (derived from tyrosine) are required to maintain adequate rates of basal energy metabolism in humans.66 Fifth, creatine (formed from arginine, glycine, and methionine) is needed to store energy as phosphocreatine for muscular work and neurological function.67 Six, carnitine (synthesized from lysine, methionine and serine) is required to transport long-chain fatty acids from the cytoplasm into the mitochondrion for β-oxidation to yield acetyl-CoA.1 Seventh, serotonin and melatonin (metabolites of tryptophan) inhibit the production of inflammatory cytokines to maintain the health of adipose tissue, while regulating food intake and behavior by humans.39 Finally, arginine, leucine, glycine, tryptophan and glutamine activate the mTOR signaling pathway to stimulate skeletal-muscle protein synthesis,41 thereby partitioning dietary energy from the fat stores into muscle building."

"The rate of skeletal-muscle protein synthesis in healthy adults is 25% higher when protein intake is evenly distributed across breakfast, lunch, and dinner, compared with a pattern where most protein is consumed at the evening meal despite the same daily intake of total protein.72 This finding has important implications for improving skeletal-muscle mass, strength and function in older, physically active adults who generally experience a resistance to the stimuli of muscle protein synthesis and have a higher threshold of dietary protein intake to promote muscle protein synthesis."

"Of note, plants do not contain taurine or carnosine.1 Additionally, protein in animal products has a higher digestibility (∼95%) than proteins isolated from plants (∼85–92%) or proteins in whole plant foods (∼80–85%) which generally contain anti-nutritional factors.3"

"Several lines of evidence show that animal-source protein has a greater nutritional value than plant-source protein to sustain skeletal-muscle mass. First, dietary supplementation of 17.5 g milk protein per day during a 12-week resistance exercise program increased lean body mass (3.9 vs. 2.8 kg) than an isonitrogenous amount of soy protein.75 Second, compared with soy protein, dietary supplementation with 24 g whey per day to young men enhanced their lean tissue gains (3.3 vs. 1.8 kg) after 36 weeks of resistance exercise training.76 Third, ingestion of animal-source protein by healthy adults ranging from 17.5 to 40 g from whey, skimmed milk, or beef stimulated skeletal-muscle protein synthesis to a greater extent than the same amount of soy protein under resting and post-exercise conditions.61 Fourth, long-term vegetarianism resulted in reduced skeletal-muscle mass in older women, compared with consumption of an omnivorous diet (18.2 vs. 22.6 kg lean body mass).77 Thus, as a nutritional strategy, adequate consumption of animal protein (e.g., nutrient-dense lean meat) can reverse the decline in protein intake by adults in the age groups of ≥51 years. This simple means is vitally important for sustaining skeletal-muscle mass and improving health in aging adults."

"Globally, plant- and animal-based foods contribute ∼65% and 35% of protein, respectively, in human diets, and the opposite is true in North America.30"

"Protein deficiency causes multiple clinical syndromes,85 which are summarized in Table 4. This nutritional problem can occur in any community at any age due to illness or poor diets, and is frequently exacerbated by inadequate energy intake.22 Dietary protein deficiency not only contributes to poor growth, cardiovascular dysfunction, and high risk of infectious disease, but also exacerbates the deficiency of other nutrients (including vitamin A and iron) and worsens metabolic profiles (e.g., dyslipidemia and hyperglycemia) in humans. This is because of the need for protein to: (a) digest and absorb dietary nutrients by the small intestine; (b) transport nutrients (including long-chain fatty acids, vitamin A, and iron) and other molecules (e.g., cholesterol and triacylglycerols) in blood; and (c) oxidize nutrients (including fatty acids and glucose) to water and CO2.86–88"

"Safe (tolerable) upper limits for dietary protein intake (maximum safe intake) by young and adult humans have not been established, and can differ among individuals. Like any nutrient, divided protein intake at different meals of the day is preferred to reduce a sudden excess of any AA in the gastrointestinal tract, liver, brain, heart, kidneys, and other tissues. As noted previously, the Institute of Medicine recommended an acceptable macronutrient distribution range for protein intake at 10% to 35% of total energy for adults. It should be borne in mind that the dietary intake of energy should not exceed requirements and that the safety of protein intake is influenced by consumption of carbohydrates and lipids. In view of large variations among people in any age population, caution must be exercised not to adopt “one shoe fits all” guidelines when establishing safe upper limits of dietary protein intake by humans."

"Long-term consumption of any nutrients (including water, protein, and vitamin A) in high amounts may have adverse effects on human health.99 Protein intake greater than its safe upper limits in different age groups can exceed the ability of the liver, intestine, and kidneys to detoxify ammonia and should be avoided. Adverse effects of high protein intake include intestinal discomfort, hyperaminoacidemia, hyperammonemia, hyperinsulinemia, dehydration, irritation, nausea, diarrhea, liver and kidney injuries, fatigue, headache, seizures, high risk of cardiovascular disease, or even death.100 Problems of high protein intake can be exacerbated by low intake of carbohydrates because of additional burdens on the liver and kidney to produce large amounts of glucose from AA besides their roles in disposing of excessive ammonia and urea. Glucose is essential for meeting the energy requirements of the brain, red blood cells, renal medullar tissues, and retinal cells, and for the production of NADPH to support numerous biochemical (including anti-oxidative) reactions. Even during long-term starvation, the human brain still utilizes a large amount of glucose (i.e., 40% of the normal uptake of 125 g per day for a 70 kg person), and this glucose is derived primarily from AA."

"Efficient absorption of dietary minerals and mineralization depend on protein.108 In addition, protein is a major component of bones. Thus, adequate intake of protein, particularly from calcium- and phosphorus-rich milk products, is essential to support bone growth in infants and children and to sustain the mass and health of the skeleton in adults. There is a concern that high protein intake may stimulate urinary excretion of calcium, which may contribute to bone loss and subsequent development of osteopenia and osteoporosis.108 However, in free-living individuals, high protein intake is likely associated with high calcium intake, and, therefore, may compensate for a moderate increase, if any, in urinary excretion of calcium. Based on an extensive and systematic review of the literature, Sahni et al.109 concluded that dietary protein provided a significant benefit on bone health in humans. Likewise, there is evidence that adequate protein intake increases peak bone mass in both young and older adults.110,111 Thus, protein nutrition plays a key role in skeletal health to reduce risk for osteopenia and osteoporosis."

"In summary, adequate consumption of high-quality protein is essential for optimal growth, development, and health in humans. An appropriate mixture of animal- and plant-based foods is a practical way to ensure balanced provision of dietary AA for the young and the adult. There is not a fixed amount of protein intake that suits all the people in all age groups. Rather, individuals should adjust their intake of protein and other nutrients according to metabolic rates, physiological needs, and health status. A sufficient supply of both EAA and synthesizable AA (so-called nutritionally nonessential AA) plays a key role in sustaining skeletal-muscle protein synthesis, mass, and function (including physical strength), while improving insulin sensitivity, ameliorating ageing-associated sarcopenia, and reducing white-fat accretion. In practice, adequate consumption of lean meat (a source of not only high-quality dietary protein but also vitamins and minerals) can help individuals realize the health benefits of moderate or intense exercise. To date, there are myths about AA and protein nutrition in humans due to inadequate understanding of the science. Sufficient intake of high-quality protein from animal products (e.g., lean meat and milk) is essential for optimal growth, development, and health of children, as well as for optimal maintenance, function and health of tissues (including skeletal muscle, brain, heart, kidneys, liver and gut) in adults. However, consumption of protein above safe upper limits should be avoided to prevent any adverse health problems."​

Great post highlighting the importance of protein. Thanks.

 

[Amazoniac]

- Response of hepatic proteins to the lowering of habitual dietary protein to the recommended safe level of intake

"The pool size of a plasma protein is a reflection of the balance between its rate of synthesis and catabolism and its partitioning between the intravascular and extravascular compartments. It has long been known that, on lower-protein diets, there is a tendency for the intravascular albumin pool to be maintained at the cost of the extravascular pool. Less clear is the extent to which this may apply to other plasma proteins. To maintain the plasma pools of RBP and TTR during consumption of 0.75 g⋅kg(−1)⋅day(−1) of protein over a period of 10 days, any reduction in their rates of synthesis would have to be matched by equal reductions in their rates of catabolism. Our data suggest that the plasma pool sizes of RBP and TTR were maintained due to the downregulation of the rates of both synthesis and catabolism as an intrinsic part of the adaptative response to the lower protein intake. The reduction in the rates of synthesis and degradation of RBP and TTR are similar to the responses in whole body protein kinetics for these same subjects while they consumed 0.75 g protein⋅kg(−1)⋅day(−1) (4)."

Spoiler

"The combination of the present results with those of earlier reports shows that, when healthy individuals decrease their protein consumption from habitual, ~1.1 g⋅kg(−1)⋅day(−1) down to 0.75 g⋅kg(−1)⋅day(−1), there is a series of metabolic responses. These responses include the downregulation of whole body protein turnover (4), a decrease in the rate of glutathione synthesis and cellular antioxidant protection (5), and a downregulation in the synthesis of individual nutrient transport proteins. These changes indicate a selective sacrifice of function and imply a limitation on the ability of healthy individuals to maintain important metabolic functions."

"The question that remains unanswered is whether this state is less than optimal and whether, for example, the reduction in the rate of synthesis of specific nutrient transport proteins in any way compromises tissue function. Although this loss of capacity may not always express itself as a change in metabolic behavior, the concern would be that there has been a loss of reserve capacity. The cost of this loss of reserve capacity would be expected to manifest itself in situations where the individual is challenged by a stressful situation or stimulus. These findings would, therefore, support the arguments put forward by Young et al. (19) that a diet that provides 0.75 g protein⋅kg(−1)⋅day(−1) in normal adults may not be adequate to mount and maintain a successful host metabolic response to stress."

"In a previous study, Jackson et al. (6) reported faster rates of synthesis of two positive acute-phase proteins in healthy subjects who had consumed a diet that provided 0.6 g protein⋅kg(−1)⋅day(−1) for 7 days. This response was associated with higher plasma concentrations of IL-6, suggesting that consumption of the average minimum requirement for protein intake had elicited an "acute-phase response" in these otherwise healthy subjects. In the present study, there was no change in the concentration of haptoglobin and fibrinogen or in the synthesis of fibrinogen. This suggested that the response of haptoglobin and fibrinogen had not been elicited at a higher protein intake that provided an increase of 0.15 g protein⋅kg(−1)⋅day(−1). These findings suggest that, although a dietary protein intake of 0.75 g⋅kg(−1)⋅day(−1) may not be sufficient to maintain synthesis of all nutrient transport proteins in healthy adults, it is sufficient to prevent a stress-like acute phase response."

"In conclusion, our present study shows that, for normal adults consuming the safe level of protein intake, 0.75 g⋅kg(−1)⋅day(−1), as recommended by FAO/WHO/UNU (3), adaptive metabolic responses are brought into play. It was not possible to maintain the rate of synthesis of important nutrient transport proteins. As a result, the metabolic capacity to cope with stress may be impaired in healthy adults consuming this amount of protein. There is a need for additional studies to be conducted to determine cellular and tissue effects of these changes in nutrient transport proteins and the minimum level of protein intake that will maintain the metabolic capacity at an acceptable level in otherwise healthy individuals."​