Adults following a low-fat vegan diet for 16 weeks ate about 357 fewer calories per day and lost weight without counting calories or reducing the overall amount of food they consumed, according to a randomized clinical trial published in JAMA Network Open.
By yourNEWS Media Newsroom.
A low-fat vegan diet may help people lose weight without deliberately eating smaller portions or tracking calories by substantially lowering the amount of energy contained in each gram of food, according to a randomized clinical trial published Aug. 17 in JAMA Network Open.
Researchers from the Physicians Committee for Responsible Medicine found that adults with overweight who switched to an unrestricted low-fat vegan diet reduced the energy density of their diets by approximately 30% over 16 weeks.
Participants ultimately consumed about 357 fewer calories each day despite no significant change in the total weight of food they ate.
The trial was designed to determine whether changing the types of foods people consume could lower calorie intake and promote weight loss without conventional calorie-restriction instructions.
Participants assigned to the vegan group were encouraged to eat a diet centered on fruits, vegetables, grains and legumes. They were not given calorie targets, portion limits or instructions to deliberately reduce the amount of food they consumed.
A control group continued eating its usual diet and likewise received no calorie or portion restrictions.
Researchers found that changing food composition rather than simply decreasing food quantity produced a considerable difference in energy intake.
Dietary energy density — calculated by dividing the total number of calories eaten in a day by the total weight of food consumed in grams — fell approximately 30% among participants following the low-fat vegan diet.
Energy density remained essentially unchanged among those in the control group.
At the same time, the vegan group reduced average calorie intake by about 357 calories per day.
The total physical weight of food consumed did not decline significantly in either group, meaning participants eating the vegan diet were generally consuming a similar quantity of food by weight while taking in substantially fewer calories.
The findings suggest that lower-calorie foods containing greater amounts of water and fiber can allow people to continue eating satisfying quantities while naturally reducing overall energy intake.
Dr. Hana Kahleova, lead author of the study and director of clinical research at the Physicians Committee for Responsible Medicine, said this characteristic of plant foods may allow normal appetite mechanisms to help regulate calorie consumption.
“When the foods you eat are lower in energy density, your body’s natural appetite signals work in your favor,” Kahleova said. “You eat until you’re satisfied, and you simply end up with fewer calories.”
Plant foods such as fruits, vegetables, whole grains and legumes typically contain substantial amounts of water and fiber relative to their calorie content. That combination increases food volume while keeping energy density comparatively low.
The study’s authors said controlled feeding research cited in the paper supports the concept that reducing dietary energy density can increase fullness while lowering calorie consumption.
Other plant-based nutrition research has similarly identified dietary fiber as an important contributor to satiety.
The researchers also observed that the degree of change in energy density was associated with weight-loss outcomes.
Participants who achieved larger reductions in dietary energy density generally experienced greater weight loss.
That association remained even after researchers accounted for changes in calorie intake, suggesting that the composition of the foods themselves may play an important role beyond the simple reduction in total daily calories.
The trial involved adults with overweight who were randomly placed into either the low-fat vegan intervention or the control group for 16 weeks.
The vegan diet was ad libitum, meaning participants could eat according to appetite rather than following prescribed portion sizes.
Researchers monitored calorie intake and food weight throughout the trial and used those measurements to calculate changes in energy density.
Neither group was instructed to restrict calories.
The approach differs from many traditional weight-loss programs, which typically begin by establishing a daily calorie goal and asking participants to consciously reduce food intake.
Kahleova said focusing instead on the foods people choose could make weight management less dependent on continually monitoring portions or resisting hunger.
“Instead of telling people to eat less, we can help them eat differently — and the results follow,” she said.
The findings indicate that a diet containing large amounts of lower-energy-density foods can reduce calorie consumption without requiring people to consciously eat less food.
That distinction may be important for long-term weight management because hunger and restrictive eating can make conventional calorie-reduction programs difficult to maintain.
The researchers concluded that dietary energy density could therefore represent a practical target for people attempting to manage their weight.
Rather than concentrating exclusively on calorie totals, an individual could emphasize foods that provide greater volume for fewer calories.
Previous research has found that low-fat plant-based dietary patterns score highly on measures of overall diet quality, while earlier clinical studies have reported that low-fat vegan diets can produce weight loss and improvements in several markers of metabolic health.
The latest trial adds evidence about why such diets may affect body weight.
Participants did not lose weight because researchers required them to consume smaller meals. Instead, the foods included in the vegan diet reduced the amount of energy contained in the same approximate weight of food, allowing participants to eat until satisfied while consuming fewer calories.
The study does not mean that all vegan foods automatically have low energy density, nor does it establish that intentional calorie restriction has no role in weight management. The intervention specifically emphasized a low-fat dietary pattern built largely around fruits, vegetables, grains and legumes.
Within that framework, however, the results suggest that lowering dietary energy density can substantially decrease spontaneous calorie intake without calorie counting.
Researchers said the strategy could offer a more sustainable alternative for some people because it shifts the emphasis from restricting the amount of food consumed to changing the composition of meals.
Over the 16-week trial, that change was associated with both lower calorie intake and weight loss while the overall weight of food consumed remained largely unchanged.
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