Low-fat vegan diet cuts dietary energy density by nearly a third in randomized trial

A randomized clinical trial published in JAMA Network Open found that a low-fat vegan diet lowered dietary energy density by roughly 30% among adults with overweight. The 16-week study assigned participants to either an ad libitum low-fat vegan diet of fruits, vegetables, grains, and legumes or a control group that made no dietary changes. Neither group received calorie limits or portion instructions.

Total food weight consumed did not change significantly in either group, meaning participants on the vegan diet ate the same amount of food by weight. However, energy intake fell by about 357 kilocalories per day in the vegan group, while the control group saw a smaller decline. Dietary energy density dropped about 30% in the vegan group and did not change in the control group.

The reduction in energy density was driven by the elimination of calorie-dense animal foods such as meat, dairy, and eggs, and a sharp increase in high-volume, low-energy-density plant foods, especially vegetables and legumes. Because these foods contain fewer calories per gram, participants could eat generous portions while consuming less energy overall.

Greater reductions in energy density were associated with greater weight loss, and the association remained after accounting for changes in calorie intake. Lead author Hana Kahleova, M.D., Ph.D., of the Physicians Committee for Responsible Medicine, said the findings help explain how people can lose weight without counting calories or going hungry.

Controlled feeding studies have previously shown that lowering the energy density of meals helps people feel full and reduces subsequent intake while keeping food volume constant. The researchers suggest that targeting energy density through food composition may offer a more practical strategy for weight management than calorie restriction or portion control.

The study was conducted by the Physicians Committee for Responsible Medicine and published in JAMA Network Open (2026) with DOI 10.1001/jamanetworkopen.2026.27483.