Dietary fibres are beneficial for our health, and scientists from DTU National Food Institute and the Department of Nutrition, Exercise and Sports at the University of Copenhagen have now uncovered an essential part of the question why this is the case. Different types of bacteria inside our colon compete to utilize an essential amino acid called tryptophan. This competition may lead to either good or bad outcomes for our health. The research, published in the scientific journal Nature Microbiology, reveals that when we eat lots of dietary fibres, gut bacteria help turn tryptophan into healthy substances. But if we don’t eat enough fibres, tryptophan can be converted into harmful compounds by our gut bacteria.
“These results emphasize that our dietary habits significantly influence the behaviour of gut bacteria, creating a delicate balance between health-promoting and disease-associated activities. In the long term, the results can help us design dietary programs that prevent a range of diseases,” says a professor at DTU National Food Institute, Tine Rask Licht.
Dietary fibres determine the battle over tryptophan
Researchers have long known that dietary fibres are directly converted into healthy short-chain fatty acids by gut bacteria in the colon. However, the new study surprisingly shows that dietary fibres also contribute to good health by preventing the conversion of the amino acid tryptophan into harmful substances and promoting its conversion into beneficial substances in the colon.
“The gut bacterium E. coli can turn tryptophan into a harmful compound called indole, which is associated with the progression of chronic kidney disease. But another gut bacterium, C. sporogenes, turns tryptophan into healthy substances associated with protection against inflammatory bowel diseases, type 2 diabetes, cardiovascular diseases, and neurological diseases," says Anurag Kumar Sinha, a researcher at DTU National Food Institute.
Through multiple experiments in bacterial cultures and mice, the researchers demonstrated that fibre-degrading gut bacteria, such as B. thetaiotaomicron, regulate the indole-forming activity of E. coli.
“B. thetaiotaomicron assists by breaking down fibres into simple sugars, which E. coli prefers over tryptophan for growth. The sugar components from the fibres prevent E. coli from turning tryptophan into indole, thereby allowing C. sporogenes to utilize tryptophan for the production of healthy compounds,” says Anurag Kumar Sinha.