Vegetarian Diets and Weight
It’s clear that creating a caloric deficit is the only way to lose weight, but how do vegetarian diets rank compared to other diets when it comes to weight loss? Further, is there typically a difference in weight between vegetarians and non-vegetarians?
Article By: The Weight Watchers Research Department
A review of the scientific literature on the subject found that 29 out of 40 studies reported that vegetarians weighed significantly less than non-vegetarians.1 This was observed in both males and females, and various ethnic groups. Although vegetarians tend to have healthier lifestyle habits that may influence weight, e.g., more exercise and less smoking, some studies were performed within a population with similar lifestyles, and the differences in weight were still seen.
Vegetarian diets and weight status
The type of vegetarian diet can also impact weight status. Results from a study of 37,875 healthy men and women participating in the Oxford cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC-Oxford) found that after adjusting for age, mean BMI was significantly highest among meat-eaters (24.41 kg/m2 in men, 23.52 kg/m2 in women) and lowest in the vegans (22.49 kg/m2 in men, 21.98 kg/m2 in women).2 Vegetarians and fish eaters had comparable mean BMI in between the other groups.
Further, vegetarians have a lower rate of overweight and obesity. Data analyzed in 55,459 healthy women that participated in the Swedish Mammography Cohort revealed a 40 percent prevalence of overweight and obesity among omnivorous women, 29 percent among semi-vegetarians and vegans, and 25 percent among lacto-ovo vegetarians.3 A vegetarian diet also may impact the accumulation of excess weight. Participants in the EPIC-Oxford Study who cut back on animal-based foods showed the lowest rate of weight gain.4
Because vegetarian diets are associated with lower body weight, rate of overweight and obesity, vegetarians may also have a lower risk of certain diseases like heart disease and diabetes.
Vegetarian diets and weight loss
Taking in fewer calories than your body needs, by either decreasing caloric intake through your diet and/or expending energy through exercise, is the only way to lose weight. One strategy that can be used to reduce caloric intake is to follow a vegetarian diet.
Research shows that following a vegetarian diet can result in, but does not guarantee successful weight loss. For example, results from a study published in January 2008 found that sedentary and overweight adults assigned to follow a lacto-ovo vegetarian diet lost an average of 7.9 percent of their body weight after 18 months. However, participants who followed a standard diet also lost 8 percent of their body weight.5 The insignificant difference in weight loss between those following a standard vs. vegetarian diet shows that it is not the type of diet that controls weight loss, but rather the caloric deficit.
Another study showed that overweight, postmenopausal women who were assigned to 14-week a low-fat, vegan diet lost 12.76 pounds (+/- 7.04 pounds) compared to 8.36 pounds (+/- 6.16 pounds) lost by those following a control diet based on National Cholesterol Education Program guidelines,6 as well as after one and two years.7
The higher weight loss seen with the low-fat, vegan diet may be attributed to its low energy density. Research has shown that incorporating low energy density foods as part of a diet can lead to greater weight loss. (For more information on energy density, read the Science Center library article, Cutting Calories: Portion Control, Energy Density).
The Weight Watchers Approach:
Any type of vegetarian diet can be incorporated into the Weight Watchers plan. However, to ensure all nutritional needs are met, some specific guidelines are provided.
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1 Berkow SE, Barnard N. Vegetarian diets and weight status. Nutrition Reviews 2006 April;64(4)175-188.
2 Spencer EA, Appleby PN, Davey GK, Key TJ Diet and body mass index in 38000 EPIC-Oxford meat-eaters, fish-eaters, vegetarians and vegans Int J Obes Relat Metab Disorder. 2003 Jun;27(6):728-34.
3 Newby PK, Tucker KL, Wolk A. Risk of overweight and obesity among semivegetarian, lactovegetarian, and vegan women Am J Clin Nutr. 2005 Jun;81(6):1267-74.
4 Rosell M, Appleby P, Spencer E, Key T. Weight gain over 5 years in 21,966 meateating, fish-eating, vegetarian, and vegan men and women in EPIC-Oxford. Int J Obesity. 2006;30:1389-1396.
5 Burke LE, Warziski M, Styn MA, Music E, Hudson AG, Sereika SM. A randomized clinical trial of a standard versus vegetarian diet for weigh loss: the impact of treatment preference Int J Obes (Lond). 2008 Jan;32(1):166-76.
6 Barnard ND, Scialli AR, Turner-McGrivy G, Lanou AJ, Glass J. The effects of a low-fat, plant-based dietary intervention on body weight, metabolism, and insulin sensitivity Am J Med. 2005 Sep;118(9):991-7.
7 Turner-McGrievy GM, Barnard ND, Scialli AR. A two-year randomized weight loss trial comparing a vegan diet to a more moderate low-fat diet. Obesity. 2007;15:2276-2281.