Many Studies Will be Excluded from Dietary Guidelines' Review, says Nutrition Coalition
On August 9th 2023, the Nutrition Coalition submitted a public comment to the expert committee that is overseeing the science for the 2020 Dietary Guidelines for Americans. Public comment periods are part of every Dietary Guidelines process, although there is some evidence that these comments have little impact on the process. Our comment below addresses important protocol issues for the scientific reviews on the "Dietary Patterns" and on saturated fats. These issues are very likely to lead to the exclusion of large bodies of scientific literature, including major clinical trials funded by the National Institutes of Health.
Dear Members of the 2025 Dietary Guidelines Advisory Committee,
We write on behalf of the Nutrition Coalition to express our concerns about the current protocol criteria of the Nutrition Evidence Systematic Review (NESR) for the systematic review on dietary patterns and growth, body composition, and risk of obesity. We are concerned that the current protocols may exclude important studies on obesity.
Specifically, as currently written, the inclusion and exclusion criteria appear likely to exclude many clinical trials on low-carbohydrate diets, despite more than 100 clinical trials demonstrating that these diets are safe and effective for combating obesity, diabetes, and heart disease.
We also write to encourage NESR to undertake a systematic review of low-carbohydrate and ketogenic diets for the 2025-2030 Dietary Guidelines for Americans (DGA) as we believe such a review will aid in the DGA’s mission to prevent chronic disease.
There are three aspects of the current NESR protocol that we believe will needlessly omit important data on how to reduce overweight and obesity.
Under Current NESR Protocol, Rigorous Data May Be Excluded
Example 1
First, it appears likely that the NESR review protocols for the Dietary Patterns (DP) will omit many clinical trials on low-carbohydrate diets. The DP protocols include the following exclusion criteria (see the protocol for body weight/risk of obesity as an example): [1]
Studies that do not provide a description of the dietary pattern, which at minimum, must include the foods and beverages in the pattern (i.e., studies that examine a labeled dietary pattern, but do not describe the foods and beverages consumed)
Nearly all low-carbohydrate and ketogenic clinical trials do not include a full description of all the foods and beverages in the pattern, because the nature of these studies is to focus primarily on limiting a single macronutrient (carbohydrate).
For example, a randomized, controlled trial on weight loss funded by the National Institutes of Health (“Effects of low-carbohydrate and low-fat diets: a randomized trial”)[2], comparing low-fat and low-carbohydrate diets, provides instructions on carbohydrate and fat limits but would be excluded under the current NESR protocol, because it does not provide a full description of all the foods and beverages in these dietary patterns.
A cursory look at other low-carbohydrate and overweight or obesity studies reveals that other randomized, controlled clinical trials using the current protocol will evidently also be omitted from the NESR review, because they do not include a complete list of food and beverages in the study protocols:
Kakoschke, N., Zajac, I. T., Tay, J., Luscombe-Marsh, N. D., Thompson, C. H., Noakes, M., … Brinkworth, G. D. (2021). Effects of very low-carbohydrate vs. high-carbohydrate weight loss diets on psychological health in adults with obesity and type 2 diabetes: a 2-year randomized controlled trial. European Journal of Nutrition.doi:10.1007/s00394-021-02587-z
Kikuchi T, Kushiyama A, Yanai M, Kashiwado C, Seto T, Kasuga M. Comparison of Weight Reduction, Change in Parameters and Safety of a Very Low Carbohydrate Diet in Comparison to a Low Carbohydrate Diet in Obese Japanese Subjects with Metabolic Disorders. Nutrients. 2023 Mar 9;15(6):1342. doi: 10.3390/nu15061342.
Guo H, Wang L, Huang X, Shen F, Lu Y, Zhang P. Effects of low-carbohydrate vs low-fat diets on weight loss and metabolic risk factors in obese/overweight individuals with impaired glucose regulation: A randomized controlled trial. Asia Pac J Clin Nutr. 2022;31(3):512-519. doi: 10.6133/apjcn.202209_31(3).0018. PMID: 36173222.
Thus, due to the NESR’s inclusion/exclusion criteria, we believe that a large number of clinical trials, which are the most rigorous form of science, will be unnecessarily excluded from the Dietary Pattern systematic reviews.
→Our strong recommendation is therefore to eliminate the criteria requiring that all food and beverages of a dietary pattern be included for a study to meet inclusion criteria.
Example 2
Second, the NESR reviews on obesity and overweight are currently structured to include only those trials that include subjects with obesity and overweight. However, there are many studies, including rigorous clinical trials, on subjects with other types of chronic disease, such as heart disease, diabetes, and hypertension, that report meaningful weight loss outcomes. These studies should also be included, since their outcome data is also meaningful and important.
It is remarkable to note that the studies that would be excluded under NESR’s current protocol include studies that have already been cited to support the DGA. For instance, a study cited as compelling evidence to support the 2015 Dietary Guidelines for Americans was a randomized trial on the Mediterranean diet[3], where the subjects had metabolic syndrome but not necessarily obesity. Ironically, under the existing NESR inclusion/exclusion criteria, this study would now be excluded from the 2025 review.
We believe it is essential not to exclude significant clinical research when formulating weight loss recommendations for the 2025 Dietary Guidelines.
→Our second recommendation is to expand the inclusion criteria for the systematic review on Dietary Patterns and overweight/obesity to include studies on any population where weight loss is an outcome measure. Specifically, subjects with other chronic diseases should be included, including those with heart disease, hypertension, metabolic syndrome, diabetes, and fatty liver disease.
Need for a Novel Systematic Review on Low-Carbohydrate Diets
Finally, we do not believe that the USDA is required to wait for the review on carbohydrates by the National Academies of Science, Engineering, and Medicine (NASEM) to conduct its own systematic review on low-carbohydrate diets.
Based on our research, there is no requirement in the National Nutrition Monitoring Act nor any US Department of Agriculture regulation for the NESR to defer to the NASEM on the matter of macronutrient proportions. In fact, for decades, the Dietary Guidelines Advisory Committee (DGAC) made determinations about the amount of allowable dietary fat without consulting the NASEM, setting a longstanding precedent in this regard.
Another consideration is that there is already a NASEM DRI report from 2005[4]. This report found:
“The lower limit of dietary carbohydrate compatible with life apparently is zero, provided that adequate amounts of protein and fat are consumed."
Carbohydrates may be consumed, of course, but they are not essential for human survival, because our bodies can synthesize glucose de novo through the process of gluconeogenesis, mainly from the proteins we consume. Most experts in the field acknowledge that carbohydrates are not essential. For example, a 2021 article authored by former DGAC member, Joanne Slavin, highlights this fact[5].
Many clinical trials have now explored the health outcomes of people consuming 0-130 grams of carbohydrates per day, and most of these trials show beneficial outcomes for preventing or reversing type 2 diabetes, hypertension, and other chronic diseases. A NESR review on this topic would be highly relevant to the DGA's mission of disease prevention.
→Our third recommendation is therefore to issue a novel systematic review of low-carbohydrate and ketogenic diets for the 2025-2030 Dietary Guidelines.
Low-carbohydrate diets have shown exceptional results[6] in preventing and treating chronic diseases. We strongly believe that disregarding this wealth of scientific literature deprives a large portion of the U.S. population of valuable insights that could aid in managing conditions like obesity, diabetes, and other related diseases.
Sincerely,
Nina Teichoz
Founder, the Nutrition Coalition
Author, science journalist
Mark Cucuzzella MD FAAFP MHP
Chair of the Scientific Council of the Nutrition Coalition
Staff Physician Martinsburg Veterans Administration Hospital
Professor West Virginia University School of Medicine
Diplomate American Board of Obesity Medicine
[1] https://nesr.usda.gov/sites/default/files/2023-05/2025-DGAC-Protocol-Dietary-patterns-Growth-bodycomposition-obesity.pdf
[2] Bazzano LA, Hu T, Reynolds K, Yao L, Bunol C, Liu Y, Chen CS, Klag MJ, Whelton PK, He J. Effects of low-carbohydrate and low-fat diets: a randomized trial. Ann Intern Med. 2014 Sep 2;161(5):309-18. doi: 10.7326/M14-0180. PMID: 25178568; PMCID: PMC4428290.
[3] Esposito K, Marfella R, Ciotola M, Di Palo C, Giugliano F, Giugliano G, D'Armiento M, D'Andrea F, Giugliano D. Effect of a mediterranean-style diet on endothelial dysfunction and markers of vascular inflammation in the metabolic syndrome: a randomized trial. JAMA. 2004 Sep 22;292(12):1440-6. doi: 10.1001/jama.292.12.1440. PMID: 15383514.
[4] Institute of Medicine. 2005. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press. https://doi.org/10.17226/10490.
[5] https://doi.org/10.1093/advances/nmab050
[6] Volek, J.S.; Phinney, S.D.; Krauss, R.M.; Johnson, R.J.; Saslow, L.R.; Gower, B.; Yancy, W.S., Jr.; King, J.C.; Hecht, F.M.; Teicholz, N.; Bistrian, B.R.; Hamdy, O. Alternative Dietary Patterns for Americans: Low-Carbohydrate Diets. Nutrients 2021, 13, 3299. https://doi.org/10.3390/nu13103299