The combination of a bacterium that normally lives in the gut and a protein-rich diet promotes a more tolerant, less inflammatory gut immune system, according to new research. Such an environment also helps with irritable bowel syndrome.
The findings, in mice, suggest a way to tilt the gut immune system away from inflammation, potentially spelling relief for people living with inflammatory bowel disease. Normally, immune cells patrol the gut to ensure that harmful microbes hidden in the food we eat don’t sneak into the body.
Cells that are capable of triggering inflammation are balanced by cells that promote tolerance, protecting the body without damaging sensitive tissues. When the balance tilts too far toward inflammation, inflammatory bowel disease can result.
Researchers found that a 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 – to trigger the cells’ appearance. They established a link between Lactobacillus reuteri bacteria that is a normal part of the gut microbiome, and the development of a population of cells that promote tolerance.
Protein-rich foods contain appreciable amounts of tryptophan: nuts, eggs, seeds, beans, poultry, yogurt, cheese, even chocolate. 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. Defects in genes related to tryptophan have been found in people with inflammatory bowel disease. The more tryptophan the mice had in their diet, the more of these immune cells they had.