Effects of Low Fat Vegan Diet on Body Weight, Insulin Sensitivity and Lipids in Overweight Adults

by | Mar 2, 2021 | 2020, Blood Lipids, Blood Sugar, Obesity, Vegetarianism, Weight Control

Written by Joyce Smith, BS. A 16-week low-fat vegan diet decreased body weight and fat and improved  glucose metabolism in study participants.

fruit and vegetablesExcess body weight and insulin resistance can lead to type 2 diabetes and other major health problems, yet obesity is uncommon in plant-based diets 1,2. High-fiber foods have low energy density which translates into larger sized portions with fewer calories.  They satiate and help control hunger unlike fats and carbohydrates (high density foods) where small portions provide more calories. A low fat-vegan diet of fruits and vegetables contains water and high fiber, requires longer digestion time and burns more calories in the digestive process, making it a desirable weight-loss diet 3,4. The “thermic effect of food” refers to the energy required to digest, absorb, and eliminate ingested nutrients and depends on the composition of the food consumed; for example, protein requires 20 to 35% of consumed calories, while carbohydrates and fats require 5 to 15% at most. There is an urgent need for dietary interventions to address today’s obesity related health problems.

The following single-center, randomized open parallel arm clinical trial 5 was designed to measure the effects of a low-fat vegan diet on body weight, insulin resistance, postprandial metabolism, and intramyocellular and hepatocellular lipid levels in overweight adults. Researchers randomized 224 adults, ages 25 to 75, from Washington, D.C. into an intervention group (n = 122) that adhered to a low-fat vegan diet and supplemented with 500 μg/d of vitamin B12. The diet consisted of approximately 75 % carbohydrates, 15% protein, and 10% fat from vegetables, grains, legumes, and fruits, but contained no animal products or added fats. The control group (n=122) maintained their regular diets for a period of 16 weeks. All participants had a BMI of 28 to 40. At weeks 0 and 16, body weight was assessed using a calibrated scale, body composition and visceral fat were measured by dual x-ray absorptiometry, and insulin resistance was assessed with the homeostasis model assessment index and the predicted insulin sensitivity index. The thermic effect of food was measured by indirect calorimetry over 3 hours following a standard liquid breakfast (720 kcal). In a subset of participants (n = 44), hepatocellular and intramyocellular lipids were quantified by proton magnetic resonance spectroscopy.

At the end of 16 weeks, the low-fat vegan diet group lost an average of 5.9 kg  (the equivalent of 13 pounds) compared to the control group who maintained their weight throughout the 4-month trial (95% CI 11-14.8 lbs., P<0.001). In addition, the low-fat vegan diet group had a 14% (95% CI 6.5-20.4, P<0.001) increase in postprandial energy expenditure (the thermic effect of food), increased the predicted insulin sensitivity index (0.9, 95% CI 0.5-1.2, P<0.001) and simultaneously decreased the homeostasis model assessment index (-1.3, 95% CI -2.2 to -0.3, P<0.001). This increase in insulin sensitivity was associated with a decrease in body weight (r=-0.43, P<0.001). In a subset of 44 participants, the researchers, using proton magnetic resonance spectroscopy, also found a significant decrease in lipid levels among those on the low-fat vegan diet: hepatocellular lipid levels decreased by a significant 34.4%, intramyocellular lipid levels by 10.4%. Both of these decreases were associated with improvements (decreases) in insulin resistance (both r=0.51, P=0.01).

In this 16-week randomized clinical trial, a low-fat plant-based dietary intervention reduced body weight by reducing caloric intake and increasing postprandial metabolism, which was associated with decreased liver and body fat and increased insulin sensitivity. These results align with previous research 6,7.

Study limitations include the self-reported dietary intake which is a source of bias. A 16-week diet is not sufficient time to evaluate the full extent of the low-fat vegan diet’s benefits and additional longer studies are required; however, the low-fat, plant-based diet may be an effective intervention for overweight adults.

Source: Kahleova, Hana, et al. “Effect of a Low-Fat Vegan Diet on Body Weight, Insulin Sensitivity, Postprandial Metabolism, and Intramyocellular and Hepatocellular Lipid Levels in Overweight Adults: A Randomized Clinical Trial.” JAMA network open 3.11 (2020): e2025454-e2025454.

© 2020 Kahleova H et al. JAMA Network Open. This is an open access article distributed under the terms of the CC-BY License.

Click here to read the full text study.

Posted March 2, 2021.

Joyce Smith, BS, is a degreed laboratory technologist. She received her bachelor of arts with a major in Chemistry and a minor in Biology from  the University of Saskatchewan and her internship through the University of Saskatchewan College of Medicine and the Royal University Hospital in Saskatoon, Saskatchewan. She currently resides in Bloomingdale, IL.

References:

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  2. Tonstad S, Butler T, Yan R, Fraser GE. Type of vegetarian diet, body weight, and prevalence of type 2 diabetes. Diabetes Care. 2009;32(5):791-796.
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  5. Kahleova H, Petersen KF, Shulman GI, et al. Effect of a Low-Fat Vegan Diet on Body Weight, Insulin Sensitivity, Postprandial Metabolism, and Intramyocellular and Hepatocellular Lipid Levels in Overweight Adults: A Randomized Clinical Trial. JAMA Netw Open. 2020;3(11):e2025454.
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  7. Ravussin E, Acheson KJ, Vernet O, Danforth E, Jéquier E. Evidence that insulin resistance is responsible for the decreased thermic effect of glucose in human obesity. J Clin Invest. 1985;76(3):1268-1273.