What are the links between intestinal microbiota and metabolic diseases?1,2

If our cells require the right fuel to carry out their various functions, this is also the case for our intestinal bacteria: the multiple essential roles they play in our great metabolic symphony have only recently been discovered. Watch out for harmful effects in the event of wrong notes…

Our intestines are home to a common base of bacteria mainly divided into two large groups: the Bacteroidetes and Firmicutes; the former being more abundant than the latter when we are healthy. However, in obese individuals, the balance tilts towards the Firmicutes. These bacterial species are thought to extract more calories from the food that we ingest–in particular complex sugars–than the Bacteroidetes, leading to excess weight.

A vicious circle of inflammation

Then, an entire cascade of “bad” reactions of the organism is activated by a diet that is too high in fat which unbalances the intestinal microbiota. The barrier function of the intestines is no longer as effective; they are less resistant and let through molecules produced by the bacteria. This triggers an abnormally persistent and silent response from the immune system. The pancreas is impacted by this chronic inflammation and produces less insulin, which in turn is less well used by our cells leading to insulin resistance, a characteristic of type 2 diabetes. Storage of fats in the tissues and their transport in the blood are also disrupted. The blood vessels are not just obstructed by fat, but also dilate less effectively. Finally, a cardiovascular bomb made up of abdominal fat, elevated blood lipids, high blood pressure and hyperglycemia leads straight to what is called metabolic syndrome.

The guardians of our metabolism

Conversely, in the case of a diet that is beneficial for our intestinal flora like the Mediterranean diet (diet rich in fruit, vegetables and olive oil, and low in meat), a virtuous mechanism is set in motion: our bacteria produce shortchain fatty acids (SCFA), a source of energy for our cells. These SCFA are involved in the regulation of appetite, bowel movements and the formation of fats. They can act on insulin production and blood pressure. Some, like butyric acid, protect the cells of our intestines from inflammation and help them fight against aggressive microbes. They are even thought to have anti-cancer properties. Not to mention the fact that bacteria produce vitamins (K, H and B) and help us to absorb calcium, magnesium, vitamin D and iron. Some researchers no longer hold back from stating that the intestinal microbiota is an organ in its own right.

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1 Pascale A, Marchesi N, Marelli C, Coppola A, Luzi L, Govoni S, Giustina A, Gazzaruso C. Microbiota and metabolic diseases. Endocrine. 2018 May 2. doi: 10.1007/s12020-018-1605-5
2 Li X, Watanabe K, Kimura I. Gut Microbiota Dysbiosis Drives and Implies Novel Therapeutic Strategies for Diabetes Mellitus and Related Metabolic Diseases. Front Immunol. 2017 Dec 20;8:1882. doi: 10.3389/ fimmu.2017.01882