Without a functioning intestinal immune system, dietary fiber found in fruits and vegetables cannot effectively help regulate blood sugar levels in the body. A study reports the discovery of a specific type of immune cell that may help convert dietary fiber into useful elements that regulate blood sugar levels. A discovery that is essential for progress in preventing metabolic disorders such as diabetes.
The intestinal immune system is an essential intermediary in the complex association between diet and metabolism: without it, the dietary fibers present in fruits and vegetables cannot participate properly in regulating blood sugar levels in the body. Researchers from Inserm and Sorbonne University have just demonstrated that a certain type of immune cell would be essential for this beneficial effect of dietary fibers on carbohydrate metabolism. These results are published in the journal Nature Communications.
The health benefits of dietary fiber, particularly found in fruits and vegetables, are now well documented: they contribute to weight management, carbohydrate and lipid balances in the body, and play a protective role against colon cancer. According to previous work, fiber is aided in its task by the intestinal immune system. The latter includes different populations of immune cells that ensure food tolerance or intervene to fight infectious agents in the intestinal wall. However, its precise role in relation to dietary fiber remains poorly understood.
A team led by Inserm researcher Emmanuel Gautier at the Cardiovascular and Metabolic Diseases Research Unit (Inserm/Sorbonne University) wanted to find out more. The scientists worked on a mouse model fed a high-fat, low-fiber diet, mimicking a “Western” diet. For four weeks, half of these animals also received a fructo-oligosaccharide (FOS) fiber supplement, which is commercially available for food use.
Links between microbiota and immune system
The scientists were able to observe that, although all the animals became overweight, those that received dietary fiber supplementation showed an improvement in the assimilation of glucose by the body, with the effect of better control of blood sugar.
To better understand the mechanisms at play, the team compared the compositions of the microbiota and the immune system of the intestine of animals that received fiber supplementation or not.
Mice not supplemented with fiber had a microbiotamicrobiota depleted with lower bacterial diversity. In addition, at least two immune cell populations were deficient in the intestine: lymphocyteslymphocytes Th17, involved in the protection of the intestinal barrier and lymphocytes TT peripheral regulators (pTreg) contributing to the tolerance of the intestinal microbiota. These alterations suggest a weakening of the local immune system, linked to the impoverishment of the microbiota.
Conversely, in mice supplemented with fiber, morespeciesspecies bacterial were maintained in the microbiota, and in particular bacteriabacteria known to stimulate the production of Th17 immune cells. In fact, this population of lymphocytes appeared to be preserved, as did that of pTreg lymphocytes.
The role of immune cells in glycemic control
” This could be explained by a contribution of fibers to the enrichment of the intestinal microbiota in bacterial species which support the differentiation of certain immune cells.specifies Adélaïde Gélineau, first author of this study. The mechanism explaining the association between these bacteria and an enrichment in certain immune cells is however not yet completely understood, especially in response to dietary variations. ” she adds.
“We managed to preserve the intestinal flora, local immunity and carbohydrate metabolism in animals fed a high-fat diet”
Finally, the team discovered the importance of a third population of immune cells called cDC2 dendritic cells. These cells are known to support the development of Th17 cells and participate in the functioning of pTreg cells. The research team therefore wanted to study their role in this context of a fatty diet with or without fiber supplementation using a mouse model deficient in cDC2 cells. They were thus able to observe their essential nature for the beneficial effect of fiber on glycemic control.
” Without these cells, fiber intake is not sufficient to preserve Th17 cells and correct carbohydrate imbalance. This central role of cDC2 dendritic cells in controlling the immune and metabolic effects of fiber was previously unknown. “, underlines Emmanuel Gautier.
” Here, with just one ingredient, FOS type fibers, we have managed to preserve the intestinal floraintestinal floraL’immunityimmunity local and carbohydrate metabolism in animals fed a fatty diet, adds the researcher. With this work, we provide insight into the cellular mechanisms by which dietary fibers beneficially impact cell metabolism. glucoseglucoseUnderstanding these interactions between diet, immunity and metabolism is a prerequisite for progressing knowledge in nutrition, particularly for assessing the impact of diets on the body and establishing recommendations. “, he concludes about these results which must now be confirmed in humans.
