Gut feeling: bacteria and diabetes

15 November 2018

Intestinal bacteria can trigger the development of conditions like type 1 diabetes, a new study has shown.

We’re often led to believe that bacteria are bad. But our skin and guts are full of friendly microbes essential to keeping us happy and healthy. In fact, the bacteria in our intestines – dubbed the intestinal microbiome - play a key role in digestion and also protect us by preventing more dangerous microbes gaining a toe-hold.

Now scientists are beginning to understand the molecular details of how bacteria in the gut are linked to complex diseases. The “Environmental Determinants of Diabetes in the Young” study has found consistent differences between the spectrum and behaviour of gut bacteria carried by healthy infants compared with children that develop type 1 diabetes.

This form of diabetes is caused by the body’s own immune system attacking insulin-secreting cells in the pancreas. Patients lose the ability to produce insulin, meaning that they cannot control their blood sugar levels.

By comparing stool samples taken every month in children from the age of 3 months, Tommi Vatanen and his colleagues at the Broad Institute in Cambridge, Massachusetts, found that the gut bacteria from healthy infants consistently produced more of a class of molecules called short chain fatty acids than bacteria carried by infants that developed type 1 diabetes.

Intriguingly, the same trend of reduced short chain fatty acid production by gut bacteria has been seen in adults with type 2 diabetes, the form of the condition commonly associated with obesity. This highlights an important connection between the behaviour of gut bacteria and the control of insulin and blood sugar levels.

Vatanen and his colleagues have also found that antibiotic treatment profoundly affects the balance of the microbiome, leading to the loss of some classes of bacteria and a relative over-growth of others. Diet can also play a role: the levels of enzymes that break down sugars in human milk decrease as breast-feeding stops, while enzymes involved in digesting fibre increase after weaning.

This sensitivity to diet could be one way to alter the course of a patient’s disease. In mice, a diet tailored to promote production of short chain fatty acids by bowel bacteria has a protective effect against diabetes. If the same effect occurs in humans, this could provide doctors with another new way to manage diabetes.

Overall, the discovery highlights how a better understanding of the bacteria living inside us will help us understand our own health and disease.

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