'Protein rich diet may provide relief from bowel disease'

Consuming foods rich in protein such as nuts, eggs, poultry and chocolates may help foster a more tolerant, less inflammatory gut environment, providing relief to people living with bowel disease, a study claims.

Researchers at Washington University School of Medicine in the US found that a kind of tolerance-promoting immune cell appears in mice that carry a specific bacterium in their guts.

The bacterium needs tryptophan, one of the building blocks of proteins, found in foods like nuts, eggs, seeds, beans, poultry, yogurt, cheese, even chocolate, to trigger the cells' appearance, researchers said.

"We established a link between one bacterial species - Lactobacillus reuteri - that is a normal part of the gut microbiome, and the development of a population of cells that promote tolerance," said Marco Colonna, professor at University of Washington.

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

If such findings hold true, it would suggest that the combination of L reuteri and a tryptophan-rich diet may foster a more tolerant, less inflammatory gut environment, which could mean relief for people living with the abdominal pain and diarrhea of inflammatory bowel disease, researchers said.

The team discovered that one group of study mice had a kind of immune cell that promotes tolerance, while a second group of study mice that were the same strain of mice but were housed far apart from the first group did not have such cells.

The mice were genetically identical but had been born and raised separately, indicating that an environmental factor influenced whether the immune cells developed.

Researchers sequenced DNA from the intestines of the two groups of mice. They found six bacterial species present in the mice with the immune cells but absent from the mice without them.

To understand how the bacteria affected the immune system, researchers grew L reuteri in liquid and then transferred small amounts of the liquid - without bacteria - to immature immune cells isolated from mice. The immune cells developed into the tolerance-promoting cells.

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.

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

People have the same tolerance-promoting cells as mice, and most of us shelter L reuteri in our gastrointestinal tracts, researchers said.

The study was published in the journal Science.