People follow vegetarian diets for a number of reasons including religious beliefs, personal values, environmental grounds, health benefits and limited food supply. Plant-based diets are consistently linked with long-term health.
People who follow a vegetarian dietary pattern are also more likely to have lower body weights compared with omnivores. The problem with a basic observation between body weight and a vegetarian diet is that it’s hard to know how much influence other positive lifestyle habits, in combination with a vegetarian diet, have. As such, researchers investigated if body weight is affected when a person is prescribed a vegetarian diet.
Researchers from the United States conducted a systematic review and meta-analysis of clinical trials involving vegetarian diets. In total, 15 clinical trials were identified that used a vegetarian diet (both vegan and lacto-ovo vegetarian) for weight loss for a minimum of four weeks. The vegetarian diets were not energy restricted so people could self-select what and how much of foods to eat. A weakness of the review was that only four of the trials included an untreated control group for a comparison.
Following a vegetarian diet resulted in an average weight loss of 3.4 kilograms, which rose to 4.6 kilograms for people who stayed on the diet for the full duration of the trial. Greater weight loss was seen in trials that had heavier participants, ran for longer periods of time, and involved older people.
A strength of the review was that it only considered trials that didn’t restrict the quantity of food eaten or include a specific exercise intervention. This helps to remove the influence that intentional energy restriction and higher levels of physical activity play in helping with weight loss.
Making a change to a vegetarian diet, even if done only for a short period, is a viable positive behaviour change to help with weight loss. It’s also a dietary pattern that is linked to many positive health benefits and is relatively free of the hype and exorbitant claims of some of today’s popular dietary fads.