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Dietary fibre and obesity

Dietary fibre protects against obesity and metabolic syndrome

A diet supplemented with inulin reduced weight gain and noticeably reduced obesity induced by a high-fat diet, which was accompanied by a reduction in the size of fat cells

Consumption of dietary fibre can prevent obesity, metabolic syndrome and adverse changes in the intestine by promoting growth of ‘good’ bacteria in the colon, according to a study led by Georgia State University. The researchers found enriching the diet of mice with the fermentable fibre inulin prevented metabolic syndrome that is induced by a high-fat diet, and they identified specifically how this occurs in the body. The paper, ‘Fiber-Mediated Nourishment of Gut Microbiota Protects against Diet-Induced Obesity by Restoring IL-22-Mediated Colonic Health,’ was published in the journal Cell Host & Microbe.

Metabolic syndrome is a cluster of conditions closely linked to obesity that includes increased blood pressure, high blood sugar, excess body fat around the waist and abnormal cholesterol or triglyceride levels. When these conditions occur together, they increase a person's risk of heart disease, stroke and diabetes.

Obesity and metabolic syndrome are associated with alterations in gut microbiota, the microorganism population that lives in the intestine. Modern changes in dietary habits, particularly the consumption of processed foods lacking fibre, are believed to affect microbiota and contribute to the increase of chronic inflammatory disease, including metabolic syndrome. Studies have found a high-fat diet destroys gut microbiota, reduces the production of epithelial cells lining the intestine and causes gut bacteria to invade intestinal epithelial cells.

This study found the fermentable fibre inulin restored gut health and protected mice against metabolic syndrome induced by a high-fat diet by restoring gut microbiota levels, increasing the production of intestinal epithelial cells and restoring expression of the protein interleukin-22 (IL-22), which prevented gut microbiota from invading epithelial cells.

"We found that manipulating dietary fibre content, particularly by adding fermentable fibre, guards against metabolic syndrome," said Dr Andrew Gewirtz, professor in the Institute for Biomedical Sciences at Georgia State. "This study revealed the specific mechanism used to restore gut health and suppress obesity and metabolic syndrome is the induction of IL-22 expression. These results contribute to the understanding of the mechanisms that underlie diet-induced obesity and offer insight into how fermentable fibres might promote better health."

For four weeks, the researchers fed mice either a grain-based rodent chow, a high-fat diet (high fat and low fibre content with 5 percent cellulose as a source of fibre) or a high-fat diet supplemented with fibre (either fermentable inulin fibre or insoluble cellulose fibre). The high-fat diet is linked to an increase in obesity and conditions associated with metabolic syndrome.

They discovered a diet supplemented with inulin reduced weight gain and noticeably reduced obesity induced by a high-fat diet, which was accompanied by a reduction in the size of fat cells. Dietary enrichment with inulin also markedly lowered cholesterol levels and largely prevented dysglycaemia (abnormal blood sugar levels). The researchers found insoluble cellulose fibre only modestly reduced obesity and dysglycaemia.

Supplementing the high-fat diet with inulin restored gut microbiota. However, inulin did not restore the microbiota levels to those of mice fed a chow diet. A distinct difference in microbiota levels remained between mice fed a high-fat diet versus those fed a chow diet. Enrichment of high-fat diets with cellulose had a mild effect on microbiota levels.

In addition, the researchers found switching mice from a grain-based chow diet to a high-fat diet resulted in a loss of colon mass, which they believe contributes to low-grade inflammation and metabolic syndrome. When they switched mice back to a chow diet, the colon mass was fully restored.

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