Certain strains of gut bacteria produce large amounts of histamine, which can cause flare-ups of pain in people with IBS. They were found in about a quarter of irritable bowel patients.
A research team had observed patients with irritable bowel syndrome for several months and found that their stools had particularly high levels of histamine when they were in severe pain. The bacterium Klebsiella aerogenes was the most important producer of histamine in germ-free mice to which the intestinal flora had been transferred from irritable bowel patients. The bacteria converted histidine, which is found in animal and vegetable protein, into histamine. This then activates the immune system and lures mast cells into the gut, which release even more histamine and other messengers that trigger inflammation and pain.
It was found that the production of histamine by the bacteria decreased significantly when the animals were fed a diet with low fermentable carbohydrates. This could explain why some patients with irritable bowel syndrome benefit from a change in diet or a FODMAP diet that avoids such carbohydrates. Some also benefit from treatments with mast cell stabilizers or antihistamines.
Prof. Giada de Palma from McMaster University in Canada is optimistic about the results: “Now that we know how histamine is produced in the intestine, we can identify and develop therapies that target the histamine-producing bacteria.”