In the 16-week randomized clinical trial, researchers with the Physicians Committee for Responsible Medicine placed participants in either a plant-based, high-carbohydrate, low-fat diet group or asked them to maintain their current diet. The plant-based diet group avoided all animal products and added oils and limited fat intake to 20-30 grams per day. There were no limits on calories or carbohydrate intake. The control group maintained their current diets, which included meat and dairy products. Neither group altered their exercise routines.
Total carbohydrate intake did not change in the control group, but increased significantly in the plant-based diet group, both as absolute intake and as a percentage of total calories. Participants focused on whole, complex carbohydrates from fruits, vegetables, whole grains, and legumes.
At the end of the trial, body mass index, body weight, fat mass, visceral fat volume, and insulin resistance decreased significantly in the plant-based diet group. There were no significant changes in the control group.
"Fad diets often lead people to fear carbohydrates. But the research continues to show that healthy carbohydrates--from fruits, vegetables, beans, and whole grains--are the healthiest fuel for our bodies," says lead study author Hana Kahleova, M.D., Ph.D., director of clinical research for the Physicians Committee for Responsible Medicine.
The study's results support previous research finding that a plant-based, high-carbohydrate diet can help with weight regulation and body composition and reduce the risk for type 2 diabetes. Another recent study published in The Lancet found that people who consume animal-based, low-carbohydrate diets have a shorter life expectancy, compared with those who consume more carbohydrates and/or more plant-based sources of protein or fat.
Complex carbohydrates are naturally rich in fiber--a nutrient found in plant foods that adds bulk to the diet without adding extra calories. Previous studies have shown that high-fiber diets are effective for weight loss and can help reduce the risk for type 2 diabetes, heart disease, and certain types of cancer.
The study has important implications, because more than 7 in 10 U.S. adults are considered overweight or obese. Approximately 30 million Americans have diabetes, while prediabetes affects 84 million more.