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Association between changes in carbohydrate intake and long term weight changes: prospective cohort study

BMJ 2023; 382 doi: (Published 27 September 2023) Cite this as: BMJ 2023;382:e073939

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Recommendations to limit starchy vegetable intake are not clearly supported by the evidence

Dear Editor

We commend Wan and colleagues for their efforts to examine associations between changes in carbohydrate intake, sources of carbohydrate intake and weight change.1 However, the present study has significant limitations.

First, the correlation between total carbohydrate intake and total energy was r = 0.85 (supplementary table 3). This suggests that those consuming more carbohydrates were consuming more energy. Thus, it is unsurprising that increased carbohydrate intake was associated with increased weight gain. Further, the authors didn’t adjust for total energy because of concerns with multicollinearity. This underscores the problematic nature of this dataset for the question the authors examined (i.e., the relationship between carbohydrate intake and weight gain). For example, data presented by the authors in table 2 specifically state that, “a 100 g/ day increase in total carbohydrates was associated with concurrent greater weight gain of 0.2 kg (95% confidence interval 0.2 to 0.2) over a four-year period.” This implies that a 584,000-kcal caloric excess (100 grams of CHO/day * 4 kcals/gm * 365 days * 4 years) resulted in 200 grams of body mass gain over 4-years or 2920 excess kcals per gram of body mass gain. These data simply do not appear to be physiologically plausible.

Additionally, the authors did not adequately consider other potential weight-related confounding factors. While modeled substitution of one serving per day of fried potatoes for all other food categories was associated with greater weight gain, each serving per day increase of non-fried potatoes was associated with smaller increases, or even reductions in weight gain. This brings into question any causal relationship between potato consumption and weight gain. As the authors indicate in the Discussion, “because changes in weight are assessed within the same four-year interval as the change in diet, reverse causation is possible.”

We also question the use of modeling based on unrealistic ‘real-world’ exchanges. For example, the volume of food that provides 100 grams of carbohydrate is much higher, and the calories much lower, for non-starchy vegetables than for starchy vegetables. A 1-cup serving of cooked green beans contains 10.2 grams of carbohydrate and 31 calories, whereas one small baked potato contains 49.3 grams of carbohydrate and 93 calories.2-3 It’s unlikely that anyone would eat 10 cups of green beans to reach 100 g of carbohydrate.

Finally, it should be noted that the authors rely on the glycemic index as the single measure of carbohydrate quality, an assumption contested within the nutrition research community 4-6 and rejected in the World Health Organization’s recently published guideline on carbohydrate intake for adults and children.7 This approach fails to assess carbohydrate foods as a matrix of nutrients and food components, nor recognize the inextricable links between carbohydrates, human health and environmental sustainability.8-10

Clinical trials have demonstrated that potato and grain consumption, alone, do not result in weight gain.11-14 We do not believe that recommendations to limit intake of starchy vegetables or grain foods are supported by the current evidence base, particularly when U.S. consumption of vegetables and the nutrients all starchy vegetables provide (i.e., fiber and potassium) remains far below recommendations.

1. Wan Y, Tobias DK, Dennis KK, Gausch-Ferre M, Sun Q, Rimm EB, Hu FB, Ludwig DS, Devinsky O, Willett WC. Association between changes in carbohydrate intake and long term weight changes: prospective cohort study. BMJ 2023;382:e073939. doi:
2. U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, 2020. Green beans, fresh, cooked with oil.
3. U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, 2020. Potato, baked, NFS.
4. Nicholls J. Perspective: The Glycemic Index Falls Short as a Carbohydrate Food Quality Indicator to Improve Diet Quality. Front Nutr. 2022 Apr 20;9:896333. doi: 10.3389/fnut.2022.896333. PMID: 35529459; PMCID: PMC9067577.
5. U.S. Department of Health Human Services, U.S. Department of Agriculture . 2015 – 2020 Dietary Guidelines for Americans. 8th ed. (2015). Available online at: (accessed March 7, 2022)
6. Sacks FM, Carey VJ, Anderson CAM, Miller ER, III, Copeland T, Charleston J, et al.. Effects of high vs. low glycemic index of dietary carbohydrate on cardiovascular
7. Carbohydrate intake for adults and children: WHO guideline. Geneva: World Health Organization; 2023. Licence: CC BY-NC-SA 3.0 IGO.
8. Nelson ME, Hamm MW, Hu FB, Abrams SA, Griffin TS. Alignment of healthy dietary patterns and environmental sustainability: a systematic review. Adv Nutr 2016;7(6):1005–25. 79.
9. Milburn MP. Indigenous nutrition: using traditional food knowledge to solve contemporary health problems. Am Indian Q 2004;28(3/4):411– 34. 80.
10. Clune S, Crossin E, Verghese K. Systematic review of greenhouse gas emissions for different fresh food categories. J Cleaner Prod 2017;140:766–83.
11. Rebello CJ, Beyl RA, Greenway FL, Atteberry KC, Hoddy KK, Kirwan JP. Low-Energy Dense Potato- and Bean-Based Diets Reduce Body Weight and Insulin Resistance: A Randomized, Feeding, Equivalence Trial. J Med Food. Published online November 11, 2022. doi:10.1089/JMF.2022.0072
12. Daniel L Smith, Jr, Rebecca L Hanson, Stephanie L Dickinson, Xiwei Chen, Amy M Goss, John B Cleek, W Timothy Garvey, David B Allison, French-fried potatoes consumption and energy balance: a randomized controlled trial, The American Journal of Clinical Nutrition, 2022;, nqac045,
13. Johnston, E., Petersen, K., & Kris-Etherton, P. (n.d.). Daily intake of non-fried potato does not affect markers of glycemia and is associated with better diet quality compared to refined grains: A randomized, crossover study in healthy adults. British Journal of Nutrition, 1-29. doi:10.1017/S0007114520000252
14. Randolph JM, Edirisinghe I, Masoni AM, Kappagoda T, Burton-Freeman B. Potatoes, glycemic index, and weight loss in free-living individuals: practical implications.. J Am Coll Nutr. 2014;33(5):375-84. doi: 10.1080/07315724.2013.875441.

Competing interests: Julie Miller Jones: Grains Food Foundation (GFF); IL CEREALES – LATAM; Groupo Bimbo (Mexico); Scientific Advisory Board of the Quality Carbohydrate Coalition Siddhartha S. Angadi: I have received consulting income from, Grains Food Foundation, Samsung, and USAF; and served on the Scientific Advisory Board for the Quality Carbohydrate Coalition in the past 5-years. Joanne Slavin: Scientific Advisory Boards: Simply Good Foods, Sustainability Nutrition Scientific Board, Quality Carbohydrate Coalition Yanni Papanikolaou: Scientific Advisory Board Quality Carbohydrate Coalition Mitch Kanter: Alliance for Potato Research and Education Kathie Beals: Potatoes, USA

31 October 2023
Julie Miller Jones
Professor Emerita, Consultant
Siddhartha S. Angadi, PhD; Joanne Slavin, PhD; Yanni Papanikolaou, MS; Mitch Kanter, PhD; Kathie Beals, PhD
St Catherine University
Department of Nutrition and Dietetics St Catherine University St Paul MN 55105