Traditional weight-loss advice has focused on reducing food intake. Recent research, however, indicates that people can lose weight by simply altering their diet’s composition. A study published in JAMA Network Open reveals that overweight individuals could shed pounds on a low-fat vegan diet while maintaining the same food quantity.
“This is really the heart of what energy density explains,” says lead author Dr. Hana Kahleova, director of clinical research at the Physicians Committee for Responsible Medicine. “There’s a tendency for individuals to eat a consistent weight or volume of food at meals regardless of calorie content.”
Dr. Kahleova emphasizes that foods high in water and fiber, such as vegetables, fruits, legumes, and whole grains, allow consumption of satisfying food volumes with fewer calories than diets centered on meat, cheese, and processed items.
The key is understanding “energy density,” the calories contained in each gram of food. The study analyzed a 16-week clinical trial with 244 overweight adults. Participants followed either a low-fat vegan diet focused on fruits, vegetables, grains, and legumes or maintained usual eating habits. Neither group was restricted by calories or amount.
Dr. Kahleova stated, “In our study, participants who shifted to a diet of vegetables, fruits, whole grains, and legumes ate the same total weight of food daily. The food’s energy density dropped by nearly 30 percent.” Vegan participants reduced energy intake by around 357 calories daily on average without altering food quantity by weight. They consumed foods lower in calories per bite.
For those not ready to switch entirely to vegan diets, Dr. Kahleova suggests prioritizing foods naturally high in water and fiber while limiting calorie-dense options. “Fill half your plate with vegetables first,” she advises. “Swap meat with beans, lentils, or tofu weekly. Opt for whole fruit instead of juice or dried varieties and minimize added oils, butter, and cheese.” Fat delivers more than double the calories per gram compared to carbohydrates or protein, making it a significant factor.
Participants weren’t required to count or target specific calories. Changing food types led to a natural calorie reduction.
Reference: Kahleova H, Znayenko-Miller T, Maracine C, Holubkov R, Barnard ND. Vegan Diets and Dietary Energy Density: A Secondary Analysis of a Randomized Clinical Trial. JAMA Netw Open. 2026;9(8):e2627483. doi:10.1001/jamanetworkopen.2026.27483.