Vegan Diet Alters Microbiome and Insulin Sensitivity, Drops Weight

BARCELONA — A low-fat vegan diet induces changes in gut microbiota that are related to altered body composition and insulin sensitivity, and result in weight loss, according to results of a randomized controlled trial in overweight/obese adults.

Over the 16-week intervention, body weight was significantly reduced in individuals on the vegan diet compared with those who stayed on their everyday (nonvegan) diet, with a loss of –5.8 kg (P < .001), which was largely because of a drop in fat mass, with a treatment effect of –3.9 kg (P < .001). Visceral fat was also significantly reduced with the vegan eating plan.

No calorie restriction was imposed in either diet.

Hana Kahleova, MD, PhD, director of clinical research at the Physicians Committee for Responsible Medicine (PCRM), Washington, DC — the main remit of which is to promote plant-based diets — led the work and will present the findings here at the European Association for the Study of Diabetes (EASD) 2019 Annual Meeting.

“This is a pretty good result of about one pound or half a kilogram [weight loss] on average per week in the vegan group,” said Kahleova.

Kahleova explained that previous work has shown individuals can lose twice as much weight on a vegan diet as a nonvegan diet with the same calorie intake. “In conducting our study, we wanted to find out why this is so,” she noted in an interview with Medscape Medical News.

The results hint at changes to the gut microbiome producing beneficial effects, she said.

“Eating a plant-based diet with ample fiber changes the gut microbiome composition for the better by feeding the right kind of bacteria…notably short-chain fatty acid producing Faecalibacterium prausnitzii, [which] deliver many metabolic benefits including weight loss, increased insulin sensitivity, and fat loss, including visceral fat loss,” she noted.

However, Emma Elvin, senior clinical advisor at Diabetes UK, cautioned that more research is needed “to understand how plant-based diets affect gut microbiota and — crucially — what distinct effects can be attributed to the diet being specifically vegan compared to it being reduced calorie before recommending the widespread adoption of a vegan approach.”

“It’s true that many of the foods in a balanced vegan diet are good for us, but that doesn’t mean all vegan diets are healthy,” she added.

“That said, evidence to date has shown certain foods in plant-based diets — such as fruits, vegetables, and wholegrains — have been associated with reducing the risk of type 2 diabetes.”

Gut Microbiome Changes of Vegan Versus Everyday Diet

For the study, 148 overweight/obese adults with no history of diabetes were randomized to follow a low-fat vegan diet (n = 73) or no dietary changes (n = 75). The average age in the vegan and control groups was 53 years and 57 years, respectively; 60% and 67% were women, respectively; and body mass index was around 33 kg/m³ in both groups.

The vegan diet contained no animal products and comprised legumes, nuts, vegetables, fruit, and wholegrains. Calorie intake was unrestricted in both groups.

The objective of the study was to test the effect of the plant-based vegan diet on gut microbiota composition, body weight, body composition, and insulin sensitivity over 16 weeks.