Low-Fat Vegan Diet Linked to Weight Loss Without Cutting Food Portions: Study - Video

A low-fat vegan diet may help people lose weight without counting calories or deliberately eating smaller portions, according to a new study published in JAMA Network Open.

Researchers analyzed data from a 16-week randomized clinical trial involving adults with overweight. Participants followed either an ad libitum low-fat vegan diet rich in fruits, vegetables, whole grains and legumes, or made no dietary changes. Neither group was given calorie limits.

The researchers focused on energy density, which refers to the number of calories contained in each gram of food. Foods such as vegetables, fruits and legumes generally have lower energy density because they contain more water and fiber.

Participants following the vegan diet reduced the energy density of their diets by about 30%. Importantly, the amount of food they consumed by weight did not significantly decrease. Instead, they were able to eat similar quantities of food while consuming fewer calories.

Daily energy intake fell by about 357 calories more in the vegan group. Greater reductions in dietary energy density were also associated with greater weight loss, even after researchers accounted for changes in calorie intake.

The researchers attributed the change mainly to replacing calorie-dense foods such as meat, dairy and eggs with larger amounts of vegetables, legumes and other plant foods. These foods can provide greater food volume for fewer calories, potentially helping people feel full without strict portion control.

The findings suggest that changing what people eat may be an alternative to simply telling them to eat less. Increasing water-rich, fiber-rich plant foods could make calorie reduction easier and potentially more sustainable.

However, the study was relatively short, and longer-term research is needed to determine whether these effects can be maintained over time.

Overall, the findings indicate that lowering dietary energy density through a low-fat vegan diet may support weight loss while allowing people to eat satisfying amounts of food without intentional calorie restriction.

REFERENCE: Kahleova, H., et al. (2026) Vegan Diets and Dietary Energy Density. JAMA Network Open. DOI:10.1001/jamanetworkopen.2026.27483.