Washington DC (US), August 18, 2026, BNN Web Staff: A low-fat vegan diet may help people lose weight without requiring them to count calories, shrink portion sizes or regularly endure hunger, according to a new clinical study published in JAMA Network Open.
Researchers found that participants following a diet focused on fruits, vegetables, whole grains and legumes consumed about 357 fewer calories per day over 16 weeks, even though they were not instructed to eat less. The overall amount of food they consumed by weight remained largely unchanged.
The findings suggest that the energy density of food — the number of calories contained in each gram — may play an important role in weight management.
In the randomised clinical trial, adults with overweight were assigned either to an unrestricted low-fat vegan diet or to a control group that made no dietary changes. Neither group received a daily calorie limit or instructions to reduce food portions.
Participants on the vegan diet experienced an approximately 30% reduction in the energy density of their diets. The researchers also observed that larger decreases in energy density were associated with greater reductions in body weight.
More Food Volume, Fewer Calories
The researchers attributed much of the change to participants replacing calorie-dense animal-based foods such as meat, dairy and eggs with foods that contain more water and fibre but fewer calories per gram.
Vegetables, fruits, legumes and whole grains can provide substantial food volume while delivering relatively fewer calories. This means people may be able to eat satisfying portions while consuming less energy overall.
Hana Kahleova, MD, PhD, director of clinical research at the Physicians Committee for Responsible Medicine and lead author of the study, said the findings help explain how plant-based eating may support weight loss without relying entirely on calorie restriction.
According to the researchers, the approach shifts the focus from simply eating smaller quantities to choosing foods that naturally have fewer calories for the same amount of food.
What Is Energy Density?
Energy density refers to the amount of energy, measured in calories, contained in a given weight of food. Foods high in water and fibre generally have lower energy density, while foods containing more fat tend to have more calories per gram.
Previous controlled feeding research has suggested that lowering the energy density of meals can reduce calorie consumption without necessarily reducing the physical amount of food eaten.
In the latest trial, energy density changed little among participants in the control group but fell substantially among those following the vegan diet.
The researchers also found that the relationship between lower energy density and weight loss persisted even after accounting for changes in calorie intake, suggesting that the composition of the diet itself may have contributed to the observed results.
A Different Approach to Weight Management
Traditional weight-loss strategies often focus on calorie counting, restricting portions or eating less. The study suggests that changing what is on the plate, rather than simply reducing how much is eaten, could offer another approach.
A diet containing more vegetables, fruits, legumes and other fibre-rich, water-rich foods may help people reduce calorie intake while maintaining food volume and satiety.
However, the study was conducted over 16 weeks, and dietary responses can vary considerably from person to person. The findings therefore add to evidence on dietary approaches to weight management rather than establishing that a vegan diet will produce the same results for everyone.
Overall, the researchers suggest that reducing the energy density of food could be a practical strategy for people seeking weight loss without relying solely on portion control or calorie counting.
