Overweight, diabetes: how sugar disrupts the microbiota

Our expert: Dr Martine Cotinat, author of I rebalance my microbiota

A study on mice, published in the journal cellshows that sugar alters intestinal flora, triggering a chain of events that leads to excess weight, metabolic diseases, and prediabetes. These results suggest that if diet is important in preventing obesity and diabetes, it is necessary to have a varied and balanced intestinal microbiota. However, certain foods such as sugar harm the quality of the intestinal flora.

Read: Everything you need to know about sugar

Diet modifies the microbiome

Dr. Ivalyo Ivanov, associate professor of microbiology and immunology at Columbia University, and colleagues studied the effects of a Western-style diet high in sugar and fat on the microbiota of mice.

After four weeks on the diet, the animals presented the characteristics of metabolic syndrome with weight gain, the appearance of insulin resistance and glucose intolerance. And their microbiomes had changed dramatically: the amount of segmented filamentous bacteria commonly found in the gut microbiota of rodents, fish and chickens had declined sharply while other bacteria increased significantly.

Microbiome changes alter immune cells

The reduction of filamentous bacteria appears essential to animal health through an effect on immune cells called Th17. The decline in filamentous bacteria reduced the number of Th17 cells in the intestine, even though these cells are necessary to prevent metabolic diseases, diabetes and weight gain.

These immune cells are mediators of cellular immunity; they play an essential role in defense against pathogens, particularly at the level of mucosal and epithelial barriers. “These immune cells also produce molecules that slow down the absorption of ‘bad’ lipids in the intestine and reduce intestinal inflammation.“, adds Dr. Ivanov. “In other words, they keep the intestine healthy and protect the body against the absorption of harmful lipids..”

Culprit: sugar or fat?

What component of the high-fat, high-sugar diet led to these changes? Ivanov’s team discovered that sugar is to blame. “Sugar eliminates filamentous bacteria and protective Th17 cells disappear as a result“, said the researcher. “When we fed mice a sugar-free, high-fat diet, they retained gut Th17 cells and were completely protected against obesity and prediabetes, even though they ate just as many calories.”

But eliminating sugar didn’t benefit all the mice. In those who did not have filamentous bacteria at the start, therefore with an altered microbiota, the elimination of sugar had no effect. The animals became obese and developed diabetes.

“This suggests that some popular dietary interventions, such as reducing sugars, may only work in people who have certain bacterial populations in their microbiota.“, says Dr. Ivanov.

In these cases, certain probiotics might be helpful. In Ivanov’s mice, filamentous bacteria supplements led to recovery of Th17 cells and protection against metabolic syndrome, despite the animals consuming a high-fat diet.

Although humans don’t harbor the same filamentous bacteria as mice, researchers believe other bacteria may have the same protective effects. The microbiota is important, but the real protection comes from Th17 cells induced by bacteria, they say.

“For optimal health, it is important not only to modify your diet, but also to improve the quality and diversity of the microbiota“, says Dr. Cotinat.

Also read the interview with Dr Martine Cotinat on the microbiota