Evidence that vegetables – the more the merrier – are good for you is legion. And here's more: Researchers who analyzed studies of people put on vegetarian or vegan diets found that they lost more than seven pounds regardless of calorie counting or exercise plans.
The study published Thursday in the Journal of the Academy of Nutrition and Dietetics comes as many people are trying to stick to – or already have abandoned – New Year's plans to lose weight with the dozens and dozens of plans on the market.
FOR THE RECORD
An earlier version of this post incorrectly referred to the Physicians Committee for Responsible Medicine as the Physicians Committee for Social Responsibility.
The good news for such people is that they "don't need to monitor portions or calories" and still can lose weight, said one of the researchers, Susan Levin, director of nutrition education at the Physicians Committee for Responsible Medicine. "This is not about moderation, it's about healthful choices."
Dieters could approach their diet with this idea: "What is the lifestyle choice I can make that's sustainable?" Levin said in a phone interview.
The researchers reviewed 15 studies focused on plant-based diets, from vegan (no animal products) to vegetarian diets in which followers eat eggs and dairy products but no meat.
Half the studies were intended to help participants lose weight; the others were to treat health concerns such as diabetes, chronic pain or arthritis.
More than half of U.S. residents are estimated to be overweight. Obesity and overweight are linked to such diseases as type 2 diabetes, heart disease and some cancers. Observational studies show that people who eat plant-based diets weigh less than those who don't, said the researchers, who are from the Physicians Committee for Responsible Medicine. That group, headed by Dr. Neal Barnard, has long been a vocal advocate for vegetarian diets and a supporter of animal welfare organizations.
The researchers wanted to learn whether such observations could be quantified, so they looked at studies in which people were put on vegetarian or vegan diets for at least a month. On average, people lost 7.48 pounds – an average that included people who did not keep to the diet. Among those who did keep to a vegetarian or vegan diet, the weight loss was just over 10 pounds.
Fifteen studies were included in the analysis. Eleven used vegan diets, which exclude meat, fish, poultry, eggs and dairy products. One of them prescribed a raw vegan diet, meaning no foods are cooked at temperatures above 118 degrees.
The study talks about plant-based diets; that distinction is important because vegetarian or vegan diets are not necessarily healthful: Plenty of chips, cookies, white bread are all free of animal products.
More weight, in general, was lost by study participants who were heavier, older and had weight loss as a goal, the authors said. "There was no significant weight-loss difference between studies using ovo-lacto-vegetarian diets and those using vegan diets" in this analysis, the authors said.
The researchers note that any one person's results can be "highly variable," but they suggest that the high fiber content and often low fat in a plant-heavy diet might be partly responsible for the results. In addition, they wrote, "some evidence suggests that low-fat, plant-based diets can increase postprandial energy expenditure."
Among the limitations of the study analysis, the authors wrote, is that many studies were excluded because they had calorie limits or exercise components.