A low-fat vegan diet can reduce the energy density of the foods people eat by about 30%, helping them consume fewer calories while still eating satisfying amounts of food. The approach was also associated with weight loss, although participants were not told to restrict calories, according to new research published in Open JAMA Network.
In a randomized clinical trial involving overweight adults, participants who followed an ad libitum low-fat vegan diet substantially reduced the number of calories per gram of food they consumed. The researchers found that greater reductions in energy density were related to lower calorie intake and greater weight loss, despite the absence of instructions to eat less.
“This helps answer a question people often ask about plant-based eating: How can you lose weight without counting calories or starving yourself?” said Hana Kahleova, MD, PhD, director of clinical research at the Physicians Committee for Responsible Medicine and lead author. “The answer is energy density. Plant foods are rich in water and fiber, so you can fill your plate, feel full, and still eat fewer calories.”
How the low-fat vegan diet was tested
The findings come from an analysis of a 16-week randomized trial involving overweight adults. Participants were assigned to an ad libitum low-fat vegan diet focused on fruits, vegetables, grains, and legumes, or to a control group that continued eating as usual without making any dietary changes.
Neither group was given a calorie goal or told to limit how much they ate. The researchers measured the energy density of each participant’s diet by comparing total daily energy intake to the total weight of food consumed, expressed as total energy (kcal per day) divided by total weight of food (grams per day).
The study produced several notable findings:
- The total weight of food consumed did not change significantly in either group, meaning that those following the vegan diet continued to eat approximately the same amount of food by weight.
- Calorie intake decreased in both groups, but the decrease was greater among those following the vegan diet, around 357 kcal/day.
- Energy density remained essentially unchanged in the control group, but fell by approximately 30% in the vegan group.
- Greater reductions in energy density were associated with greater weight loss, and that relationship held even after the researchers accounted for changes in calorie intake.
Same amount of food, fewer calories
The difference was largely due to changes in the types of foods the participants ate. The vegan diet eliminated high-calorie animal foods, such as meat, dairy, and eggs, while increasing consumption of foods that provide more bulk with relatively few calories, particularly vegetables and legumes.
Because these plant foods generally contain fewer calories per gram, participants could continue to eat generous portions while consuming less energy overall.
“It’s not about willpower or smaller portions,” Dr. Kahleova said. “It’s about choosing foods that naturally provide fewer calories in each bite. A 30% reduction in energy density is a substantial change that would be very difficult to achieve and sustain through portion control alone.”
Why energy density can affect weight loss
Energy density refers to the number of calories contained in each gram of food. Scientists have studied it for years because it can influence how much people eat and how satisfied they are after a meal.
Controlled feeding studies have shown that reducing the energy density of meals can help people feel full while reducing the amount of energy they consume. Importantly, the physical volume of food can remain similar even when the calorie content decreases.
“When the foods you eat are lower in energy density, your body’s natural appetite signals work in your favor,” Dr. Kahleova said. “You eat until you’re full and you just end up with fewer calories. That’s a sustainable way to manage weight.”
A different approach to weight control
Weight loss tips often emphasize calorie restriction and smaller portions. These findings point to another possible strategy: changing the composition of the foods on the plate rather than simply reducing the amount of food consumed.
Choosing more high-water, high-fiber plant foods can help people reduce their calorie intake while still eating enough to feel satisfied. That could make weight management easier for some people by reducing the feeling of deprivation that can come with traditional calorie-reducing methods.
“From a clinical point of view, focusing on energy density offers a realistic strategy for weight loss,” Dr. Kahleova said. “Instead of telling people to eat less, we can help them eat differently, and the results show.”
The conclusion
The findings suggest that a low-fat vegan diet can substantially reduce the energy density of the diet, allowing people to consume fewer calories and lose weight without intentionally restricting their calorie intake.
“You don’t need to eat less,” Dr. Kahleova said. “You can eat more food, feel full, and still lose weight by choosing foods that are naturally lower in energy density.”