Eat Plant Foods for Healthy Body Weight

After reading the previous blogs on the effects of various phytoestrogens and weight loss, many of you may ask: is the plant-based diet overall beneficial for weight management? The short answer is yes.

Studies have consistently shown that vegetarians have a lower body mass index (BMI) than otherwise comparable non-vegetarians, with differences typically in the region of 1–2 kg/m2 across all adult age groups, vegans generally having the lowest BMI. These differences are reflected in a lower prevalence of obesity among western vegetarians, and lower weight gain in vegetarians and vegans during adulthood (1).

According to the 1994–1996 Continuing Survey of Food Intakes by Individuals, vegetarians in the United States have a mean BMI of 22.1 as compared with a mean BMI of 25 among non-vegetarians. A meta-analysis in 2001 of 36 studies in women and 24 studies in men showed no significant difference in height between vegetarians and non-vegetarians; however, vegetarians had significantly lower weight (-7.7 kg for men and -3.3 kg for women, p < 0.001 both, respectively) and a 2-point lower BMI (2).

Plant-based diet not only is associated with reduced prevalence of overweight and obesity but also associated with significant weight loss in overweight people, despite the absence of prescribed limits on portion size or energy intake.

In a free-living setting, 64 overweight, postmenopausal women were randomly assigned to a low-fat, vegan diet or a control diet without energy intake limits for 14 weeks. Bodyweight in the intervention group decreased 5.8 ± 3.2 kg, compared with 3.8 ± 2.8 kg in the control group (p <0.05). In a regression model of predictors of weight change, including diet group and changes in energy intake, thermic effect of food, resting metabolic rate, and reported energy expenditure, significant effects were found for diet group (p < 0.05), thermic effect of food (p < 0.05), and resting metabolic rate (p < 0.001) (3).

Individuals in the vegan group lost more weight than those in the control group at 1 year (-4.9 kg vs. -1.8 kg; p < 0.05) and at 2 years (-3.1 kg vs. -0.8 kg; p < 0.05). Those participants offered group support lost more weight at 1 year (p < 0.01) and 2 years (p < 0.05) than those without support. Attendance at meetings was associated with improved weight loss at 1 year (p < 0.001) and 2 years (p < 0.01) (4).

Overweight participants (n = 75) were randomized to follow a low-fat vegan (n = 38) or control diet (n = 37) for 16 weeks. Changes in fat intake expressed as percent of total energy consumed correlated positively with changes in fat mass (r = 0.52; p < 0.001; and 0.347; p = 0.006, respectively), even after adjustment for changes in body-mass index (BMI) and energy intake (0.33; p = 0.01). The study findings demonstrated that, in the context of a low-fat vegan diet, decreased intake of saturated and trans fats and increased relative content of polyunsaturated fatty acids, particularly linoleic and α-linolenic acids, were associated with decreased fat mass and insulin resistance, and enhanced insulin secretion (5).

To the parents out there, childhood overweight and obesity are on the rise with a big concern. Beyond age 3 years old, the likelihood that an overweight condition or obesity will persist into adulthood is positively associated with a child's advancing age. Once an obese child reaches age 6 years old, there is a 50% probability that obesity will persist. Of greatest concern is that 70–80% of obese adolescents will remain obese as adults. Also, data from the Harvard Growth Study has shown that being overweight during the adolescent years predicts adult morbidity from several chronic diseases and mortality from all causes regardless of adult body weight (2).

I have seen parents giving cakes and sweet treats often to their children and enjoying their "chunky" looks. While the pictures of the kids are adorable, sometimes I feel the need to point out that overweight status during childhood has negative health consequences well into their adulthood.

All parents want the best for their children, which includes their optimum physical health. Introducing a variety of plant foods to a child is one of the good things a parent can do. When my son was attending kindergarten, on the ride to the kindergarten, I used to give him two romaine lettuce leaves, one in each of his hands, by the time we got there, he would have eaten them. This became a routine, which helped to foster his liking for vegetables from his early age. He has been staying in a healthy weight range since then now into adulthood. No matter it may be carrots or apples or bananas or even lettuces, eating more plant foods will help to achieve healthy weight goals.

References:

1. Appleby, P. N., & Key, T. J. (2015). The long-term health of vegetarians and vegans. Proceedings of the Nutrition Society, 75(03), 287–293.

2. Sabaté, J., & Wien, M. (2010). Vegetarian diets and childhood obesity prevention. The American Journal of Clinical Nutrition, 91(5), 1525S–1529S.

3. Barnard, N. D., Scialli, A. R., Turner-McGrievy, G., Lanou, A. J., & Glass, J. (2005). The effects of a low-fat, plant-based dietary intervention on body weight, metabolism, and insulin sensitivity. The American Journal of Medicine, 118(9), 991–997.

4. Turner-McGrievy, G. M., Barnard, N. D., & Scialli, A. R. (2007). A Two-Year Randomized Weight Loss Trial Comparing a Vegan Diet to a More Moderate Low-Fat Diet*. Obesity, 15(9), 2276–2281.

5. Kahleova, H., Hlozkova, A., Fleeman, R., Fletcher, K., Holubkov, R., & Barnard, N. (2019). Fat Quantity and Quality, as Part of a Low-Fat, Vegan Diet, Are Associated with Changes in Body Composition, Insulin Resistance, and Insulin Secretion. A 16-Week Randomized Controlled Trial. Nutrients, 11(3), 615.