Low Carb Or High Carb? Everything In Moderation … Until Further Notice

Mito

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A pooling of eight large cohort studies from around the world--including PURE, ARIC, NHANES, NHS, etc.--shows the lowest all-cause mortality for people with a carbohydrate intake between 50 and 70%.


This editorial refers to ‘Lower carbohydrate diets and all-cause and cause-specific mortality: a population-based cohort study and pooling of prospective studies’, by M. Mazidi et al., doi:10.1093/eurheartj/ehz174.


In this issue of European Heart Journal, Mazidi et al.1 report an analysis of the prospective National Health and Nutrition Examination Survey (NHANES) cohort from the USA, set in the context of other prospective studies with a meta-analysis, examining the relationship between lower carbohydrate diets and mortality. From NHANES, they report that high adherence to a lower-carbohydrate diet increases the risk of death from any cause by 32%, cancer death by 35%, coronary heart disease death by 51%, and cerebrovascular disease death by 50%. The highest adherence to a diet jointly lower in carbohydrate and higher in protein increases the risk of death from any cause by 21%, cancer death by 22%, coronary heart disease death by 44%, and cerebrovascular disease death by 41%. These findings are supported by an accompanying meta-analysis: a pooled analysis of primary and secondary prevention cohorts with 5–30 years’ follow-up, conducted in the USA, Sweden, Greece, and Japan, most of which show associations in the same direction as NHANES [22% for all-cause mortality (24% when limited to primary prevention studies); 13% for cardiovascular mortality; and 8% for cancer mortality].

NHANES is a nationally representative USA survey. In this study, 24 825 participants were followed for 144 months, over which time 3432 total deaths were recorded, including 827 cancer deaths, 709 heart disease deaths, and 228 cerebrovascular disease deaths. Trained staff measured diet using two 24-h dietary recalls with the automated multiple-pass method, the survey’s standard practice since 2002.2 This technique requires short-term memory, is less burdensome, and less likely to alter eating behaviour than food records, and can be used with diverse populations and people with low levels of literacy.3 Because two recalls are administered, usual dietary intake distributions can be estimated after adjusting for day-to-day variation. The authors control for several confounding factors including age, sex, race, education, marital status, poverty to income ratio, total energy intake, physical activity, smoking, alcohol consumption, body mass index (BMI), waist circumference, hypertension, serum cholesterol, and diabetes.

The limitations of the NHANES analysis include use of self-reported dietary intake which typically underestimates total energy intake2,3 and some macro- and micronutrients.4Under-reporting bias in energy intake is proportionate to reported total energy intake, and is likely greater in overweight and obese people, and women.5 This concern is mitigated in the present analysis by adjustment for dietary energy using the residual method.6 Another limitation is that participants who complete the recalls are probably not representative of those who do not, leading to potential selection bias. In the NHANES study, those in the lowest carbohydrate score quartile were younger, male, more likely to be Mexican-American and less likely to be Black, less educated, more impoverished, less physically active, consumed more alcohol, more likely to smoke, consumed less polyunsaturated fat, saturated fat, and fibre, and were more likely to have diabetes. Thus, a lower carbohydrate diet may serve as a proxy for any of these factors, which are involved in multiple pathways to mortality. Although the authors carefully adjusted for cholesterol, blood pressure, and other risk factors in the final analyses, the possibility of residual confounding by unmeasured confounders, imprecise measurement, or misclassification cannot be ruled out.

The association between lower carbohydrate diets and death may not hold across all regions of the globe, notably in studies where total carbohydrate contributes a larger percentage of energy than in Western countries. Because the authors’ primary aim was to examine the joint effects of low carbohydrate and high protein, they excluded from their meta-analysis studies which looked at these macronutrients individually.7 In NHANES, the lowest carbohydrate group consumed 39% of energy from carbohydrate, and the highest, 66%. In the meta-analysis, the lowest carbohydrate groups consumed 26–52% carbohydrate, and the highest carbohydrate groups, 54–73%. Compared with the highest carbohydrate group, the lowest carbohydrate group had a 22% [95% confidence interval (CI) 6–39%] increased risk of total mortality. These results can be compared with the Prospective Urban Rural Epidemiology (PURE) study of 135 335 middle-aged men and women from 21 countries, in which diet was assessed by country-specific validated food-frequency questionnaires. In the PURE study, the lowest carbohydrate group consumed 48% of energy from carbohydrate (18% protein, 34% fat) and the highest, 76%.7 The lowest carbohydrate group compared with the highest carbohydrate group has a hazard ratio for total mortality of <1.0 (Mahshid Dehghan, personal communication). Interestingly, four of eight studies included in the meta-analysis with compatible data show a U-shaped association between carbohydrate and mortality: both lower and higher carbohydrate intake is associated with increased mortality. (Figure 1A).

Low carb or high carb? Everything in moderation … until further notice
 
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Methods section is informative. Part of me wants to commend their efforts. However, the limitations section highlights how meaningless self-reported dietary data is in determining mortality risk.
 

lampofred

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Excess carbs are bad if you are converting them into lactic acid. Low carb is bad if you are burning fat and breaking down protein. The optimal is the amount you can oxidize into CO2, and it's different for everyone based on their history of PUFA intake, stress, etc.
 

Kelj

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Everything in moderation, including moderation.
Oscar Wilde
 

Dino D

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Excess carbs are bad if you are converting them into lactic acid. Low carb is bad if you are burning fat and breaking down protein. The optimal is the amount you can oxidize into CO2, and it's different for everyone based on their history of PUFA intake, stress, etc.
How do you know that? I mean how do I now when I am eating to much carbs?
 

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