Beans, beans, the magical fruit—the more you eat, the more weight you lose.  

That’s according to a new study by the Journal of the Academy of Nutrition and Dietetics that explored how following a low-fat vegan diet impacted the food groups people choose, nutrient intake and diet quality—and how those changes impacted markers of health, including weight and insulin sensitivity (J Acad Nutr Diet. 2022;S2212-2672[22]00235-0). 

Vegan diets and other diets that minimize meat consumption, such as vegetarian, flexitarian and plant-based diets, are growing in popularity among consumers, as evidenced by the burgeoning market for plant-based meat and dairy alternatives. In fact, the International Food Information Council’s (IFIC) 2022 Food & Health Survey found 12% of Americans reported they have adopted a plant-based diet.  

While a vegan diet has been associated with a range of health benefits, such as improved joint health, research has also shown that the quality of a vegan diet can impact its potential healthfulness.  

The present study, published in the Journal of the Academy of Nutrition and Dietetics, enrolled 219 healthy adults with a body mass index (BMI) between 28 and 40. Participants were asked to either follow a low-fat vegan diet or make no diet changes over a period of 16 weeks. In addition to following a low-fat vegan diet—a diet comprising only about 10% of calories from fat—participants in the intervention group also attended weekly classes that provided dietary instruction, group discussion and education on the health effects of plant-based eating. 

Researchers tracked changes in diet, including changes in intake of food groups and macronutrient and micronutrient intake; changes in diet quality; and changes in body weight, body composition and insulin sensitivity. Diet quality was measured using the Alternate Healthy Eating Index-2010 (AHEI-2010). 

Researchers found weight loss was most strongly associated with greater consumption of legumes and decreased consumption of meat, fish and poultry.  

“Increased legume intake was the best single food group predictor of weight loss,” study authors wrote. The results showed participants following the vegan diet ate about 0.8 additional servings of legumes each day, which was associated with decreases in weight, fat mass and visceral adipose tissue compared to control. Total meat, fish and poultry intake decreased by about 3.5 servings compared to the control group.  

Participants who followed the vegan diet intervention also increased the amount of fruit and nonstarchy vegetables they consumed by about 0.7 and 1 servings each day, respectively. Eating more fruit, the study showed, was associated with weight loss. Eating more vegetables was not. In addition, the diet group increased whole grain and meat alternatives (tofu, tempeh and vegies burgers) intake, while decreasing intake of dairy products, eggs, added fats, nuts and seeds.  

Diet quality, as measured by the AHEI-2010, increased an average of six points among those who followed a vegan diet, compared to control. Researchers attributed the change in diet quality to an increased score in the fruits, vegetables, nuts and legumes, red/processed meat, trans fat and whole grains categories. Notably, vegan dieters saw a decreased score for polyunsaturated fatty acids and long-chain fatty acids. 

“These data suggest that increasing low-fat plant foods and minimizing high-fat and animal foods is associated with decreased body weight and fat loss, and that a low-fat vegan diet can improve measures of diet quality and metabolic health,” researchers wrote.