When the researchers doubled the amount of tryptophan in the mice's feed, the number of such cells rose by about 50 percent but when tryptophan levels were halved, the number of cells dropped by half.

It is not known whether tryptophan byproducts from L. reuteri induce the cells to develop in people as they do in mice, but defects in genes related to tryptophan have been found in people with inflammatory bowel disease.

And the bacterium needs tryptophan one of the building blocks of proteins to trigger the cells' appearance.

The more tryptophan the mice had in their diet, the more of these immune cells they had.'

Potentially, high levels of tryptophan in the presence of L. reuteri may induce expansion of this population.'

When the active component was purified from the liquid, it turned out to be a byproduct of tryptophan metabolism known as indole 3 lactic acid.

He suggested if the same works in humans, a combination of L. reuteri and a tryptophan rich diet may foster a more tolerant, less inflammatory gut environment.

While sufferers are usually advised to dodge meat and dairy to soothe their symptoms, researchers at Washington University found protein's essential amino acid tryptophan helps develop immune cells that foster a tolerant gut.