Following a vegan diet promotes gut health and weight loss, lowers diabetes risk by 23%

09 September 2020

Vegan diet

A vegan diet high in complex carbohydrates can help you lose weight and lower your diabetes risk, according to a study from the Physicians Committee for Responsible Medicine in Washington.

The researchers said that changes to gut health caused by the diet may have to do with the improved outcomes. However, that further research is needed to establish the connection between the two.

These findings, presented at the Annual Meeting of the European Association for the Study of Diabetes in Barcelona, illustrate that a calorie-restricted diet high in complex carbohydrates (e.g., dietary fiber) benefits people with diabetes, contrary to the belief that high-carb diets increase one’s risk of the condition.

Weight loss and better insulin sensitivity linked to changes in gut health

In the study, researchers examined how a 16-week plant-based diet affects gut microbiome composition, body weight, body composition and insulin resistance in overweight adults with no history of diabetes.

They pooled 148 people, of which 73 switched to a low-fat vegan diet for four months while the rest stuck to their usual diets. At baseline and after 16 weeks, they measured gut microbiome composition, body composition and insulin resistance.

Results showed that the vegan group increased their insulin sensitivity and reduced their body weight by as much as 15.2 lbs or 6.9 kg — a result of a reduction in fat mass and in visceral fat.

Moreover, the amounts of two gut bacteria, Faecalibacterium prausnitzii and Bacteroides fragilis, increased in the vegan group. Changes in these two bacterial strains are associated with decreases in body weight, fat mass, visceral fat and insulin sensitivity. According to the researchers, the high-fiber content of the diet may have caused these changes.

“The main shift in the gut microbiome composition was due to an increased relative content of short-chain fatty acid-producing bacteria that feed on fiber. Therefore, high dietary fiber content seems to be essential for the changes observed in our study,” explained the researchers.

The bacteria F. prausnitzii, in particular, break down plant complex sugars and starch to produce butyrate and other short-chain fatty acids (SCFAs). SCFAs have beneficial effects on body weight, body composition and insulin sensitivity. (Related: Vegan diet found to markedly improve health of diabetes patients.)

However, the researchers are keen to note that more research is needed to clarify the association between the changes in gut microbiome and the improvements in body weight and metabolic health. Other experts also expressed their qualms in making easy correlations in the study.

“Without other information, simple correlations cannot prove causality,” said Ian Johnson of the Quadram Institute in Norwich. Dr. Johnson was not part of the study.

King’s College London‘s Tom Sanders, who was also not part of the study, echoed Dr. Johnson’s sentiment. But he added that the study does highlight how high intake of unrefined carbohydrates in a calorie-restricted diet may be good for diabetics. Carbohydrates are the main source of energy in humans. They are broken down into glucose and have three main types: starch, fiber and sugar.

Sanders said that people commonly mistake carbohydrates as bad for diabetics. But as the study shows, it depends on the type of carbohydrate. While simple carbs and sugar do elevate blood glucose levels, complex carbs like fiber can help normalize them.

Adherence and quality of foods, key to better results

The study underscores the importance of eating the right food for better health. Fiber, for example, is shown to be good for gut health.

But just as important is dietary adherence, defined by the World Health Organization as “the extent to which a person’s behavior — following a diet and executing lifestyle changes — corresponds with agreed recommendations from a health care provider.” (Related: Changing food choice and dietary habits requires breaking old behavior patterns.)

In fact, a study from the Harvard T. H. Chan School of Public Health examined nine studies that explored how dietary patterns can affect the risk of Type 2 diabetes. Results showed that those who adhered more strictly to plant-based diets had a 23 percent lower risk of Type 2 diabetes than those who did not. This suggests that adopting a high-fiber, plant-based diet like the vegan diet is beneficial not just for diabetics, but also for people who are at-risk of the disease.

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