A low-fat vegan diet was linked to lower liver fat, weight loss and better blood sugar control in a small study of adults with type 2 diabetes.
But there is an important limitation: Everyone in the study followed the same diet. Without a comparison group, researchers cannot tell how much of the improvement came from the vegan diet itself versus eating fewer calories and losing weight.
The 16-week study, published in BMJ Open Diabetes Research & Care, included 25 adults with type 2 diabetes. Participants were asked to eat a low-fat vegan diet built around vegetables, grains, legumes and fruit. They were told to eat until full rather than count calories or measure portions.
Researchers from the Physicians Committee for Responsible Medicine led the study. The organization also helped fund it, along with grants from the National Institutes of Health. Several authors were compensated by the Physicians Committee for their work on the study.
By the end of the study, participants had lost an average of about 13 pounds, or 6.6% of their starting weight.
Liver fat fell by 33%, and fat around the abdominal organs also decreased. HbA1c, a measure of average blood sugar over the previous few months, fell from 7.6% to 6.6%. Measures of how well the body responded to insulin also improved.
“For years, people with diabetes have been told to count calories and measure portions,” said lead author Hana Kahleova, director of clinical research at the Physicians Committee.
Participants in this study were not given a calorie target. But according to their food records, they still ate about 346 fewer calories per day by the end of the study.
That matters because eating fewer calories and losing weight can themselves reduce liver fat and improve blood sugar control.
The researchers acknowledge that they cannot determine whether the changes were caused by the composition of the vegan diet, the lower calorie intake, the weight loss or a combination of all three.
Another important finding was that some of the weight loss came from lean mass.
Participants lost about 9 pounds of fat mass and about 5 pounds of lean mass. The researchers said future studies should look at whether resistance exercise or greater attention to protein intake could help preserve lean mass, especially in older adults with type 2 diabetes.
The study also involved a relatively small and motivated group of participants. People using insulin, GLP-1 medications and several other treatments were excluded.
The findings are still notable because the researchers measured more than body weight alone, including liver fat and several markers related to blood sugar control.
But larger controlled trials are needed before researchers can say how much benefit comes from the diet itself.
The study was funded by the Physicians Committee for Responsible Medicine and grants from the National Institutes of Health. Several authors received compensation from the Physicians Committee for their work on the study. Neal Barnard serves without compensation as president of the organization and receives royalties and honoraria for nutrition-related books, articles and lectures.