Guru, I went for a more careful read of your previous classes on this minimum requirement. Here's one of the publications that thou post'd:
- Dietary Methionine Restriction Increases Fat Oxidation in Obese Adults with Metabolic Syndrome
It's interesting. Hopefully divine forces draw Daniel Wich here for him to opine about the 'plasma methionid' test.
Anyway, your experiment led me to everything that follows..
From what I understand, below they used a method that judges sufficiency by enough protein synthesis when the required amino acids are present. If there are missing ones, those that is in excess will disposed by burning them for energy. They pick phenylalanine for this purpose and radiolabel a part of it to detect its excretion (that should've been incorported instead).
- Total sulfur amino acid requirement in young men as determined by indicator amino acid oxidation with l-[1-13C]phenylalanine
"Total sulfur amino acids (SAAs) are the first limiting amino acids in several foods (9); therefore, knowledge of the mean requirement and population-safe intake of SAAs is important for making recommendations about protein and amino acid intakes in humans."
"[..]because nitrogen balance tends to underestimate nitrogen losses and is influenced by excess energy intake, amino acid requirements are susceptible to underestimation (12–16)."
"The first published estimates of total SAA requirements were based on the nitrogen balances of 6 men (11). The current population-safe intake of SAAs for adults recommended by the FAO/WHO/UNU is 13 mg·kg−1·d−1 (10), which is based on the highest estimated individual requirement to achieve positive nitrogen balance in studies carried out by Rose et al (11) in men and by Reynolds et al (36) in women. Human nutrient requirements, except for energy, are set according to a statistical model that uses the mean requirement plus 2 SDs to determine a population-safe intake for a given nutrient (37). In nitrogen balance studies used to estimate total SAA requirements, one can easily calculate a mean requirement and an SD because individual data are provided for each of the 6 subjects in the original paper by Rose et al (11). When we recalculated this nitrogen balance data, we found a mean requirement of 13.2 mg·kg−1·d−1. To this new mean, we added 2 times the SD to arrive at an estimated population-safe total SAA intake of 18 mg·kg−1·d−1. This value is similar to the population-safe intake found in the present study (21 mg·kg−1·d−1) and is consistent with the 24-h balance estimates discussed below (17,38)."
"Given the complexity of SAA metabolism, estimating total SAA requirements by direct oxidation tracer methods is extremely difficult. This is because the carboxyl carbon of methionine is not directly lost to the bicarbonate pool, nor is it irreversibly oxidized to carbon dioxide during degradation; a condition that must be met for the principles of direct oxidation to apply (15). However, Young et al (17) suggested that the current FAO/WHO/UNU population-safe SAA intake of 13 mg·kg−1·d−1 is too low on the basis of 24-h balance studies using l-[methyl-2H3,1-13C]methionine as a tracer. In that study, 5 men were fed 13 mg SAAs·kg−1·d−1 and tracer oxidation was monitored over 24 h. Although all of the subjects did not achieve balance at that intake, some subjects were close enough to zero balance for the authors to conclude that the true mean total SAA requirement was not much different from the FAO/WHO/UNU population-safe intake (17). The authors also suggested that for all subjects to achieve methionine balance, the population-safe intake should be set at ≈25 mg·kg−1·d−1. These results were confirmed in a later study (38)."
"IAAO is an independent method of estimating indispensable amino acid requirements in humans. Since its first applications in humans (23), IAAO has evolved into a relatively noninvasive and efficient means of elucidating the indispensable amino acid needs of children and adults (26,28). The technique monitors the oxidation of an independent, indispensable indicator amino acid in response to graded intakes of an indispensable test amino acid. As the intake of the test amino acid approaches its requirement, the oxidation of the indicator decreases such that further increments in the test amino acid will have no effect on the oxidation of the indicator amino acid (25)."
"In the present study, we found a mean total SAA requirement of 12.6 mg·kg−1·d−1, with a population-safe intake of 21.0 mg·kg−1·d−1. This latter amount is 60% greater than the current recommended total SAA requirement of 13.0 mg·kg−1·d−1 (10). Both the mean and safe IAAO-determined values agree with values predicted from 24-h balance data (17,38) and values recalculated from early nitrogen balance data (11). We conclude that 12.6 mg·kg−1·d−1 is a reasonable estimate of the average SAA requirement (37,40). Setting a dietary reference intake for total SAAs will depend on the analysis of more individual data, which may modify our current estimated population requirement of 21 mg·kg−1·d−1."
"Ensuring adequate B-vitamin nutriture when attempting to study SAA metabolism is of the utmost importance."
"Each subject randomly received each of 6 dietary methionine intakes: 0, 6.5, 13.0, 19.5, 26.0, and 32.0 mg·kg−1·d−1. Each study consisted of a 2-d adaptation period to a prescribed diet. The diet provided 1.0 g protein·kg−1·d−1 and was followed by a single study day on which phenylalanine kinetics were measured with the use of l-[1-13C]phenylalanine at 1 of the 6 dietary methionine intakes and a crystalline amino acid intake of 1.0 g·kg−1·d−1. The dietary study periods were separated by ≥1 wk; all subjects completed all 6 studies within 3 mo."
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There's a cavern by them that it's possible for others needs to not be met in spite of the adequate protein synthesis, but the experiment was on requirements for methionine dispensing the need for cysteine. When cysteine is not present, the mean minimum requirement of these pimps was about 12.5 mg/kg/d, and more (21 mg/kg/d) if they was to cover most people (just like it happens when you have to generalize recommendations for a larger population). If both are present, needs should be reduced.
The next publication is the 2 mg/kg/d experiment that seems to be the source of your suggestion. It was on people dealing with cancre and the restriction was a form of starvation where tumors are more impacted than the person, and this should have an overall positive effect.
- Nutrient Intake and Nutritional Indexes in Adults With Metastatic Cancer on a Phase I Clinical Trial of Dietary Methionine Restriction
"Although [methionine's regenerating] enzymes [dependent on folate/cobalamin and betaine] are functional in some tumors (4), most tumors are dependent on exogenous, preformed methionine and, therefore, fail to grow, even in the presence of homocysteine (5–8)."It wasn't low in cysteine. You'll find various other experiments that require methionine restriction using that product (Hominex-2 by Abbott), and its composition makes up for the lowered methionine content. It's the opposite of casein, that happens to be high in methionine and low in cysteine. Check this out:
"The selective antitumor activity of methionine restriction is not due to an absolute difference between benign and malignant tissues, because neither can survive for long in the complete absence of methionine. Rather, tumors are more sensitive than normal tissues to methionine restriction; just as many tumors are more sensitive to chemotherapy and radiation therapy. In contrast, restriction of other essential amino acids is either very toxic or ineffective (19). Methionine restriction, therefore, does not represent indiscriminate 'starvation.'"
"The protocol for implementing the dietary methionine restriction was modified over the course of the study to develop a dietary pattern that could best be used by free-living cancer patients. All patients were placed on Hominex-2 Amino Acid-Modified Medical Food (Ross Products Division, Abbott Laboratories, Columbus, OH), which is approved for treatment of patients with homocystinuria (Table 2). Hominex-2 contains essentially no methionine (Table 3). The quantity of Hominex-2 consumed daily by each patient was calculated to provide 0.6–0.8 g protein/kg body wt. Hominex-2 dose and energy intake were maintained at baseline levels throughout participation, rather than reduced as patients lost weight. Hominex-2 served as the primary dietary protein source for all patients."
"Weight loss was the only side effect of the diet, and all but one patient regained weight on resumption of a normal diet. The only patient who failed to regain weight after discontinuing the study had cancer cachexia related to pancreatic adenocarcinoma even before his enrollment. Plasma methionine levels and food records indicated that patients adhered to the diet."
"After observing weight loss in Patients 1–4, we refined the diet to provide increased energy and protein intake. Nonetheless, Patients 5–8, who maintained energy intakes considerably above baseline and protein intakes above the RDA, still lost weight at the same rate as Patients 1–4. One possible explanation for this observation is that 35 kcal/kg/ day, which was consumed by Patients 5–8, was still inadequate to maintain positive nitrogen balance. This possibility is supported by early studies showing that energy requirements are considerably higher for patients whose sole nitrogen source consists of purified amino acids than for those who consume intact proteins (21)."
"Alternatively, weight loss experienced by patients in the trial may have been independent of energy intake but, rather, attributable to 'obligatory' muscle catabolism related to methionine restriction per se. A recent study designed to quantify dietary methionine requirements in normal subjects sheds light on this issue (22). In that study, stable isotope methods were used to measure obligatory methionine oxidation in normal subjects on a diet completely devoid of sulfur amino acids (methionine and cysteine) for 5 days. Although somewhat controversial (23), obligatory oxidation rates are considered by many to represent the minimum requirement for amino acids, that is, the amount that is oxidized despite maximal body conservation. The obligatory oxidative loss of methionine was 13 mg/kg/day in that study (22). Patients in our trial, who were restricted to 2 mg methionine/kg/day, therefore, consumed 11 mg/kg/day less than the minimum requirement. However, they consumed adequate amounts of cysteine, which is present in Hominex-2. They therefore may have had obligatory methionine oxidation rates 13 mg/kg/day. The fact that all patients reversibly lost weight, despite what would normally be considered adequate energy and protein intake, may actually be encouraging, since it confirms that patients adhered to the diet. The basic premise of this strategy is that dietary methionine restriction will have a greater deleterious effect on tumors than on normal host tissues."
Therefore I don't think it's a reliable reference for minimum requirements.
Regarding this sparing effect..
- Dietary cysteine reduces the methionine requirement in men
"The current FAO/WHO/UNU population-safe intake of total sulfur amino acids (SAAs) in healthy adults, based on early nitrogen balance studies (1–3), is 13 mg·kg−1·d−1 (4). We previously reported that this value is 60% lower than the population-safe intake found in a study of men by indicator amino acid oxidation (IAAO) (5[↑↑]). Using l-[1-13C]phenylalanine as an indicator, we found that the mean methionine requirement of 6 men in the absence of dietary cysteine was 12.6 mg·kg−1·d−1 and the upper limit of the 95% CI of this mean, which is an estimate of the population-safe intake, was 21 mg·kg−1·d−1 (5). Recent studies of SAA kinetics in humans confirmed, with the use of labeled methionine tracers (6,7), that the current FAO/WHO/UNU recommendations for total SAA intake (4) are too low. In addition, using individual data provided in the early nitrogen balance study by Rose et al (1), we recalculated the mean and population-safe intake of total SAAs to be 13.2 and 18 mg·kg−1·d−1, respectively. Both of these recalculated values are similar to those found in our previous IAAO study (5) and further confirm that the population-safe intake of SAA is greater than the published FAO/WHO/UNU value of 13 mg·kg−1·d−1 (4)."
"The ability of cysteine to reduce the quantitative requirement for methionine in humans was reported in early studies (2,8–10). In contrast, a more recent series of reports on methionine kinetics using methionine and cysteine tracers suggests that cysteine has no sparing effect on methionine requirements in humans (7,11–15). However, the failure to detect a sparing effect in these recent experiments may have resulted from the investigators unknowingly supplying inadequate dietary SAA intakes. The test diets adopted in these kinetic studies were based on the FAO/WHO/UNU estimates, which we (5) and others (6,7) maintain are too low. To detect a cysteine sparing effect on methionine requirements, cysteine must be present in amounts adequate to completely, or largely, arrest the flow of metabolites through the transsulfuration pathway, whereas methionine must be present in amounts adequate to meet all its other metabolic functions, including protein synthesis, transmethylation, and the provision of homocysteine for remethylation reactions necessary for folate and betaine metabolism. Unless the total SAA needs of all subjects are met, addition of cysteine to the diet will lead to an immeasurably small sparing effect on methionine requirements (13,14)."
"Each subject randomly received each of 6 dietary methionine intakes: 0, 2.5, 5.0, 7.5, 10.0, and 13.0 mg·kg−1·d−1. Dietary cysteine was held constant at an intake of 21 mg·kg−1·d−1. Each study consisted of a 2-d adaptation period to a prescribed diet (17). The diet provided 1.0 g protein·kg−1·d−1 and was followed by a single study day on which phenylalanine kinetics were measured with the use of l-[1-13C]phenylalanine at 1 of the 6 dietary methionine intakes and a protein intake of 1.0 g·kg−1·d−1. The study dietary periods were separated by ≥1 wk; all subjects completed all 6 studies within 3 mo."
"In the current experiment we found a mean methionine requirement of 4.5 mg·kg−1·d−1 and a population-safe intake of 10.1 mg·kg−1·d−1 when cysteine was fed at an excess of 21 mg·kg−1·d−1."
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Less methionine to reach the breakpoint this time, so needs are reduced and lower amounts are enough to prevent other amino acids from being wasted.
"The evidence in support of cysteine having a sparing effect on methionine requirements in humans and animals is substantial. As early as 1941, Womack and Rose (8) showed a 17% sparing effect of cysteine on methionine requirements in rats when growth rates were used as an indicator. Shortly thereafter, a series of nitrogen balance studies in men and women showed a sparing effect ranging from 48% to 89% (2,9,10). In addition to these studies, subsequent studies showed that dietary cysteine suppresses transsulfuration in rats (26,27) and humans (11), thus providing a metabolic basis for the sparing effect of cysteine on methionine requirements."
"The available evidence indicates that the sparing effect of cysteine is based on a repartitioning of homocysteine between competing pathways. Although no change appears to occur in the rate of homocysteine remethylation to methionine by either of the available remethylation pathways (11,26,27), there is a clear reduction in the rate of transsulfuration. The net result is that the fractional remethylation of homocysteine increases while that portion metabolized by transsulfuration decreases."
The protein consumption in these experiments wasn't extreme, around the 0.8 g/kg/d standard recommendation and up to 1 g. I'm mentioning this because I was wondering if it wasn't a matter of having shoved down amino acids on these guys and increasing their requirement for methionid along.
There were subjects needing more or less but the mean value was 4.5 mg/kg/d conditioned to the higher cysteine intake. I'm not aware of foods being able to provide this much cysteine without methionine.
It seems to me that the 2 mg/kg/d value is too low even for cultures that eat little animal protein, are skinny and small, simpler lives, no stimulants, low calories, and so on; all supportive for reducing the need for it. According to such figure, a person weighing 55 kg would require at least 110 mg, but they certainly obtain this from diet, possibly more than double, making it difficult to judge how low you can go without issues.
Contrary to that, liver challenges, military stress, generalized malnutrition making the person unable to compensate for the lack of methionine, wasting, etc, should all increase the requirements above normal.
I'm sure you remember the quotes below, they mention the accumulation, yet in some cases still find it useful to give more.
- Treatment Of Cirrhosis Of The Liver By A Nutritious Diet And Supplements Rich In Vitamin B Complex
"although the choline and methionine content in the cirrhotic liver may be normal or actually higher than normal,[8a] these factors are not available for utilization"
"Experimental studies demonstrated that an inadequate level of methionine cannot be compensated for by excessive levels of choline and cystine.[10] It was further demonstrated that when methionine was added to choline in experimental hepatic damage and growth, a 50 per cent improvement in therapeutic results occurred.[10,15] The damaged liver thus appears to have lost its transmethylation ability and requires both synthetic methionine and choline until normal transmethylation can take place from the ingested food."
"It has been suggested that the lipotropic agent methionine could enhance in a synergistic way the lipotropic (or fatty-cirrhosis-preventing) activity of choline.[7] Animal experiments revealed further that in hepatic damage choline would largely prevent the cirrhosis but not the necrosis and hemorrhage. Methionine was found to effectively prevent both types of damage to the liver. Experimental studies also showed that the cirrhotic symptoms due to choline deficiency result from lack of a methyl-containing essential other than choline and that methionine can directly supply this lack.[8] It is now apparent that although diets may contain an adequate supply of choline, an imbalance or deficiency of other dietary constituents can nullify the lipotropic action of the choline.[9]"
"The high protein diet which I prescribed consisted not only of a high casein source of proteins by the use of skimmed milk feedings and cottage cheese but also of servings of meat three times a day wherever possible. The importance of a high protein diet in cirrhosis of the liver is now thoroughly established[13] and takes precedence over dietary carbohydrate in therapeutic importance. The maximum use of meat in this diet appeared to be advisable because of the necessity for providing the essential amino acids which contain the basic methyl groups, with and without the sulfur radical. These methyl groups are required by the liver for the transmethylation function which institutes regeneration and healing in cirrhosis. As has previously been stated, cirrhosis of the liver when produced experimentally is now regarded as a methyl-group deficiency disease."
"Second, in a controlled series of 62 patients over an eight year period,[11] therapeutic results suggested that the combination of methionine and choline resulted in a better therapeutic response than did various other combinations of amino acids, diet, liver and vitamin supplements in the treatment of hepatic cirrhosis. Methionine was taken orally in capsule form, the dosage being 2 Gm. daily. Similarly, choline chloride was administered orally in a daily dosage of 2 Gm.[10d]"
- Protective CO2 and aging
"The age accelerating effect of methionine might be related to disturbing the methylation balance, inappropriately suppressing cellular activity."
Collagen should buffer it and avoid the inappropriate effect. Those researchers mentioned gelatin in their articles, they've considered it (and some used it). To me it doesn't look like increasing everything but methionine and choline would lead to better outcomes. Do you think that they would had fared better if these were cut to the minimum consistently? When do you think that more is desirable?
If anything, it's the uncompensated prolonged restriction that is concerning the most:
- Treatment Of Cirrhosis Of The Liver By A Nutritious Diet And Supplements Rich In Vitamin B Complex
"Interestingly, in contrast to pure methionine restriction, combined methionine and choline restriction have prooxidant, proinflammatory effects in the liver [92,93] and may even promote the development of liver cirrhosis [94] and hepatocellular carcinoma [95]. Methionine- and choline-deficient (MCD) diet in mice also induces liver steatosis and may be used as a suitable model for investigation of the pathophysiological mechanisms of NAFLD [96]. In 2 weeks MCD diet induces focal microvesicular liver steatosis, while in 6 weeks inflammation accompanies diffuse micro- to macrovesicular steatosis with increased serum level of C-reactive protein [93]. These changes are associated with increased levels of malondialdehyde and nitrites+nitrates and reduced GSH level, thus indicating that MCD diet causes oxidative and nitrosative stress in the liver. Additionally, the antioxidative capacity of the liver was found to be decreased by MCD diet due to the reduction of superoxide dismutase and catalase activities, the reduction being the most extensive after 4 week-treatment with MCD diet [93]. Lack of methionine and choline in the diet was also found to cause alterations in free fatty acid profile in the liver [92]. Within 2 weeks it causes a decline in palmitic, stearic, arachidonic and docosahexaenoic acid (DHA). The significance of this finding should be further investigated, but a decrease in DHA level may at least partially contribute to the proinflammatory effect of MCD diet on the liver [92]. All of these changes are dominantly caused by choline deficiency. However, although choline deficiency is sufficient for the development of steatosis, both methionine and choline deficiency are essential for the development of inflammation in the liver [97]. These findings clearly indicate, that adequate intake of micronutrients according to daily requirements is a prerequisite for beneficial effects of dietary methionine restriction on metabolic processes and function of the liver."
As they said in the human study, methionine restriction diet (MRD) are reliable mimics of caloric restriction (CR) and achieve the same lifespan extension. I don't see how MRD would be harmful if it can pull this off. Considering methionine is an essential amino acid, of course if you completely remove it from the diet there will be issues down the road. Until we know more how much methionine is safe (at the upper limit) I would not take any more than what is in the diet. Same applies to cysteine. Just as you mention the evidence for liver damage from lack of methionine, there is also evidence for liver and heart toxicity at increased daily intake too.
Effect of methionine dietary supplementation on mitochondrial oxygen radical generation and oxidative DNA damage in rat liver and heart
"...Methionine restriction without energy restriction increases, like caloric restriction, maximum longevity in rodents. Previous studies have shown that methionine restriction strongly decreases mitochondrial reactive oxygen species (ROS) production and oxidative damage to mitochondrial DNA, lowers membrane unsaturation, and decreases five different markers of protein oxidation in rat heart and liver mitochondria. It is unknown whether methionine supplementation in the diet can induce opposite changes, which is also interesting because excessive dietary methionine is hepatotoxic and induces cardiovascular alterations. Because the detailed mechanisms of methionine-related hepatotoxicity and cardiovascular toxicity are poorly understood and today many Western human populations consume levels of dietary protein (and thus, methionine) 2–3.3 fold higher than the average adult requirement, in the present experiment we analyze the effect of a methionine supplemented diet on mitochondrial ROS production and oxidative damage in the rat liver and heart mitochondria. In this investigation male Wistar rats were fed either a L-methionine-supplemented (2.5 g/100 g) diet without changing any other dietary components or a control (0.86 g/100 g) diet for 7 weeks. It was found that methionine supplementation increased mitochondrial ROS generation and percent free radical leak in rat liver mitochondria but not in rat heart. In agreement with these data oxidative damage to mitochondrial DNA increased only in rat liver, but no changes were observed in five different markers of protein oxidation in both organs. The content of mitochondrial respiratory chain complexes and AIF (apoptosis inducing factor) did not change after the dietary supplementation while fatty acid unsaturation decreased. Methionine, S-AdenosylMethionine and S-AdenosylHomocysteine concentration increased in both organs in the supplemented group. These results show that methionine supplementation in the diet specifically increases mitochondrial ROS production and mitochondrial DNA oxidative damage in rat liver mitochondria offering a plausible mechanism for its hepatotoxicity."
The atherogenic effect of excess methionine intake
"...Mice fed methionine-rich diets had significant atheromatous pathology in the aortic arch even with normal plasma homocysteine levels, whereas mice fed B vitamin-deficient diets developed severe hyperhomocysteinemia without any increase in vascular pathology. Our findings suggest that moderate increases in methionine intake are atherogenic in susceptible mice. Although homocysteine may contribute to the effect of methionine, high plasma homocysteine was not independently atherogenic in this model. Some product of excess methionine metabolism rather than high plasma homocysteine per se may underlie the association of homocysteine with vascular disease."