The microbial community in the human gut plays a central role in various diseases. An important form of chemical communication between the gut microbiome and the human body comes from small molecules produced when bacteria in the digestive system breaks down food. These include acids such as acetate, propionate, and butyrate. These fermentation products in the gut can regulate the immune system, promote the regeneration of the intestinal mucosa and influence human behaviour. Although these effects are known, the daily dose of these molecules to which the human body is exposed was previously unknown.
Precise calculation of molecular exchange
In a new study, published in the journal, Cell, researchers at ETH Zurich and Stanford University have precisely quantified how many of these molecules are produced by gut bacteria and arrive in the body every day. The researchers used data from people's diets and daily stool production. This enabled them to calculate how many gut bacteria are used up and regenerated each day. In the lab, they measured how many fermentation products the bacteria must produce to replace the bacterial mass.
"Our findings provide a detailed picture of how intensively the gut microbiota and the host exchange substances," says Markus Arnoldini, first author of the study. "This knowledge is crucial for understanding exactly how the gut microbiome influences our health."
Diet influences the concentration of messenger substances
The study's analysis can also be used to calculate how the concentration of molecules changes when we adjust our diet or the composition of our gut bacteria changes. While changes in the composition of gut microbes can influence the types of fermentation products, this has only a minor effect on the total concentration. A change in diet, on the other hand, has a much greater impact on the amount of fermentation products.
A clear example of this is the energy that the human body can obtain from these products. In a modern Western diet, fermentation products cover only 2 to 5 percent of daily energy demand. In contrast, this proportion can reach up to 10 percent in a more traditional diet – the researchers used data from the Hadza, a hunter-gatherer people in Tanzania.
"The precise quantification of these molecular signals forms an important basis for future research," explains Markus Arnoldini. "Our methods could help to investigate changes in the daily dose of bacterial fermentation products in specific disease patterns such as colon cancer or chronic inflammatory bowel disease more precisely."
