Multiple sclerosis (MS) is an autoimmune disease with an uncertain cause. However, recent research has linked it to gut microbes. We know that the Western diet, full of processed “foods” and remarkably high in sugar, is associated with many diseases, and we may soon be able to add MS to that list.

What is it about the Western diet that is so unhealthy? It appears to be the impact of those manufactured foods on the microbes that live in the gut, the microbiota. In particular, it seems that a species of helpful bacteria, Prevotella histicola, is being steadily exterminated by the Western diet. That is largely due to the diet’s lack of prebiotics, the fiber that feeds microbes in the colon.

Using a mouse model of MS, researchers found that by feeding the mice P. histicola, they could reduce the symptoms. Apparently P. histicola is able to chill out the immune system and prevent it from attacking the mouse’s own cells. If this work translates into humans, it will be a welcome development, as current treatments can have unpleasant side effects.

Because it affects the brain and because depression is common among MS sufferers, P. histicola acts here as a psychobiotic.