Hana Kahleova, MD: Plant-Based Diet Impact on Weight Loss, Gut Microbiota

Hana Kahleova, MD, PhD

A recent study has found that following a low-fat vegan diet can induce changes in gut microbiota related to changes in weight, body composition, and insulin sensitivity.

The study, from investigators at the Physicians Committee for Responsible Medicine, observed the impact of a plant-based diet on overweight patients in a randomized clinical trial.

A total of 148 participants were included in the study and were randomized in a 1:1 ratio to a low-fat vegan group or to a group without diet changes. At baseline and, again, at week 16, investigators analyzed gut microbiota using uBiome kits, body composition using dual energy X-ray absorptiometry, and PREDIM index to analyze insulin sensitivity at baseline and, again, at week 16.

After analyses, investigators noted significant reductions in body weight among those in the vegan group (treatment effect -5.8 kg [95% CI, -6.9 to -4.7 kg]; p<0.001). Additionally, they noted a reduction in fat mass (-3.9 kg [95% CI, -4.6 to -3.1 kg]; p<0.001) and in visceral fat (treatment effect -172 cm3 [95% CI, -308 to -37 kg]; p=0.01).

An abundance of faecalibacterium prausnitzii in the vegan group. Relative changes in faecalibacterium prausntizii correlated negatively with changes in body weight (r=-0.26; p=0.008), fat mass (r=-0.26; p=0.008), and visceral fat (r=-0.25; p=0.01). Investigators added that a relative abundance of bacteroides fragilis increased in the vegan group and relative changes correlated negatively with changes in body weight (r=-0.48; p<0.001), fat mass (r=-0.48; p<0.001), visceral fat (r=-0.24; p=0.02), and positively with changes in PREDIM (r=0.36; p=0.0004).

Lead investigator Hana Kahleova, MD, PhD, director of clinical research with the Physicians Committee for Responsible Medicine, recently sat down with MD Magazine® to discuss the results of the trial.

MD Mag: What were the results of your randomized clinical trial into changes in gut microbiota in response to a plant-based diet.

Kahleova: So, we've known for quite a long time that plant-based diets work well for the treatment of diabetes and also for diabetes prevention, however we wanted to look into the mechanisms behind the beneficial effects of plant-based diets and gut bacteria is an emerging area of research connecting the dots between inflammation, insulin resistance, fatty liver disease, and also diabetes.

So, we decided to look into the gut microbiome composition in people who were overweight and were insulin resistant, but who had not had diabetes yet. So, we looked at their gut microbiome composition at baseline and then we randomized them to follow a vegan diet — a plant-based diet &mdash; or to stay on their usual diet for 16 weeks to account for seasonal fluctuations and stuff like that and we had 147 participants that were randomized in this clinical trial and, as expected, all the metabolic outcomes improved in the vegan diet.

So, people were losing weight — 5.8 kilograms on average over the course of 16 weeks &mdash; and two-thirds of the weight loss was due to fat loss. We were measuring the body composition using a DEXA scan and people were losing visceral fat and were improving their insulin sensitivity and these metabolic outcomes were also related to the changes in gut microbiome.

More specifically, we found out that the whole family of bacteroidetes increased in response to the vegan diet and, more specifically, the short chain fatty acid producing bacteria like cyclic bacteria prausnitzii increased, which was a super positive finding because decreased amounts of Faecalibacterium prausnitzii have been found in patients with type 2 diabetes and have been also associated with increased inflammation and increased insulin resistance. So, increasing of faecalibacterium prausnitzii is one of the short chain fatty acid producing bacteria is a very positive finding and, more importantly, these changes in faecalibacterium prausnitzii were also associated with the positive metabolic outcomes, with the weight loss, and loss in fat mass and loss in visceral fat.

Another bacteria that played a role in switching to the vegan diet was bacteroides fragilis which decreased in both groups however it decreased less on the vegan diet so the treatment effect was positive and these change the changes in bacteroides fragilis were also related to changes in weight loss and also changes in fat mass and insulin sensitivity.

Our study highlights the importance of fiber, fiber intake for the prevention of diabetes because these short chain fatty acid producing bacteria feed on fiber and produce the short chain fatty acids that have positive metabolic benefits. That's why it's important for people who are at risk of developing diabetes to consume high amounts of fiber. So, unprocessed plant foods are rich in fiber and should their consumption should be encouraged.