By Ellen Feldman, MD
Altru Health System, Grand Forks, ND
This long-term prospective study found that adults on low-carbohydrate diets rich in plant-based and whole grain sources of protein and fat experienced significantly less weight gain than those on other types of low-carbohydrate diets.
Liu B, Hu Y, Rai SK, et al. Low-carbohydrate diet macronutrient quality and weight change. JAMA Netw Open 2023;6:e2349552.
Atkins, ketogenic, paleo, and South Beach diets are among the many low-carbohydrate diet (LCD) strategies adopted by individuals aiming to enhance their overall health.1-4 Although short-term clinical trials have demonstrated a correlation between these diets and weight loss, there is a noticeable gap in evidence regarding their long-term effectiveness on weight management and overall health improvement.5 To bridge this gap and to delve deeper into how specific nutrients in LCDs contribute to weight loss, Liu et al undertook a comprehensive prospective study.
The research harnessed dietary data from three major U.S. cohort studies — Nurses’ Health Study (NHS) 1 and 2 and the Health Professionals Follow-Up Study (HPFS). These ongoing studies collect biennial information on various lifestyle choices and health conditions, providing a rich dataset for analysis.6,7 Participants from these studies with conditions such as diabetes, many types of cancer, and other chronic disorders associated with weight changes were excluded from the study. After applying these and related exclusion criteria, the research focused on 103,320 female nurses from NHS 1 and 2 and 20,012 male health professionals from the HPFS.
Every four years, participants provided their dietary intake information through a semiquantitative food frequency questionnaire (FFQ). Based on these responses, the researchers categorized LCDs into five distinct types:
- Total LCD (TLCD) general reduction in carbohydrate intake;
- Animal-based LCD (ALCD) protein and fat primarily from animal sources;
- Vegetable-based LCD (VLCD) protein and fat predominately from plant sources;
- Healthy LCD (HLCD) higher in plant protein, lower in refined carbohydrates, including healthy fats, such as mono and polyunsaturated fats; and
- Unhealthy LCD (ULCD) higher in processed carbohydrates, more animal protein, and unhealthy fats, such as saturated fats.
Participants were assigned an LCD score ranging from 0-30, with higher scores indicating a stronger adherence to the LCD. The change in LCD score over each four-year interval was calculated, and the results were classified into quintiles. Participants with the largest decreases in LCD scores, moving from highly adherent to less adherent to diet, were placed in Q1, while Q5 incorporated participants with the largest increases in LCD scores, indicating an increase in LCD adherence. Q3 served as the reference group, with little to no change in diet adherence. Five to seven four-year cycles were analyzed for each of the three cohort groups. Factors such as race, ethnicity, and socioeconomic status and other variables were adjusted for in the final analysis.
Overall, participants gained a mean 1.2 kg over each four-year cycle. All results are multivariable adjusted. The results indicate that increasing TLCD, ALCD, and ULCD scores (reflecting greater adherence to diet) was associated with more weight gain, while increasing HLCD score was associated with less weight gain.
The VLCD group showed a unique pattern, with little variation in weight change from Q1 to Q5. Liu et al noted that participants from NHS2 in the VLCD group did show significantly less weight gain in Q5 compared to Q1, but that this association was not seen with participants from either of the other two cohorts.
Multiple subgroups were analyzed to better understand these results. In general, younger participants (< 55 years), those less physically active, and those classified as overweight or obese were more likely to experience less weight gain when adhering to HLCD compared to their counterparts.
COMMENTARY
This comprehensive, prospective study illuminates the intricate relationship between LCDs and change in weight over time, emphasizing the significance of the quality of the macronutrients. LCDs rich in high-quality macronutrients, such as whole grain and plant-based foods, were linked to less weight gain, in contrast to LCDs high in animal protein, animal fat, and refined carbohydrates, which were associated with greater weight gain.
The need for such a detailed investigation has been apparent for some time. While there have been randomized and prospective trials looking at LCDs and weight change, findings have been mixed. For instance, the A-to-Z trial (2007) found that participants on the Atkins diet experienced more significant weight loss compared to those on higher carbohydrate diets.8 Conversely, the DIETFITS trial (2017), comparing a healthy low-fat, higher carbohydrate diet with a healthy LCD, showed no significant weight loss difference between the two groups.9 Likewise, the recent Tammi et al study failed to establish a link between the amount of carbohydrate consumption and weight change.9 It may be that the nutritional quality of the macronutrients is as crucial, if not more so, than the absolute quantity.
Moreover, the definition of what precisely constitutes an LCD remains ambiguous. In the context of this study, LCDs accounted for 30% to 40% of daily energy intake, whereas the typical American diet includes carbohydrates comprising around 50% of daily energy.10 Establishing a clear, universally accepted definition for LCDs would significantly contribute to clarifying research and recommendations in this area.
While this study offers valuable insights, it is not without its limitations. Predominately, the reliance on self-reported data for both weight and dietary habits and patterns poses a challenge to the accuracy of the findings. Future research could benefit from technological advances that allow for more objective and precise monitoring of dietary intake and physical measurements.
Another limitation is the homogeneity of the study’s participants, who were all educated health professionals, which may challenge the generalizability of results. Future research would benefit from a more diverse participant pool, reflecting the critical importance of conducting long-term health surveys among a nationally representative population. Finally, given the prospective nature of this study, it is important to recognize that causation is not established.
Overall, this study has immediate practical implications for clinical practice. Diet and nutrition hold immense importance to overall health and wellness. Informing patients interested in weight management as part of a broader health and fitness plan that focusing on plant-based, unrefined carbohydrates, fat, and protein may positively affect efforts at weight loss is a relevant message. This study implies that this strategy may be most effective for younger, overweight or obese, less physically active individuals — a demographic that faces heightened risk for negative health outcomes.
REFERENCES
- Atkins. https://www.atkins.com
- Gordon B. What is the ketogenic diet? Academy of Nutrition and Dietetics. Reviewed Dec. 11, 2023. https://www.eatright.org/health/wellness/diet-trends/what-is-the-ketogenic-diet
- Mayo Clinic Staff. Paleo diet: What is it and why is it so popular? Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/paleo-diet/art-20111182
- Goff SL, Foody JM, Inzucchi S, et al. BRIEF REPORT: Nutrition and weight loss information in a popular diet book: Is it fact, fiction, or something in between? J Gen Intern Med 2006;21:769-774.
- Nordmann AJ, Nordmann A, Briel M, et al. Effects of low-carbohydrate vs. low-fat diets on weight loss and cardiovascular risk factors: A meta-analysis of randomized controlled trials. Arch Intern Med 2006;166:285-293.
- Nurses’ Health Study. https://nurseshealthstudy.org
- Health Professionals Follow-Up Study. Harvard School of Health. https://www.hsph.harvard.edu/hpfs/
- Gardner CD, Kiazand A, Alhassan S, et al. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: The A TO Z Weight Loss Study: A randomized trial. JAMA 2007;297:969-977.
- Hauser M, Hartle J, Landry MJ, et al. Association of dietary adherence and dietary quality with weight loss success among those following low-carbohydrate and low-fat diets: A secondary analysis of the DIETFITS randomized clinical trial. Am J Clin Nutr 2024;119:174-184.
- Shan Z, Rehm CD, Rogers G, et al. Trends in dietary carbohydrate, protein, and fat intake and diet quality among U.S. adults, 1999-2016. JAMA 2019;322:1178-1187.
