Just like bacteria transform milk into yogurt or cabbage into sauerkraut billions of microbes in the human gut ferment undigested food producing beneficial byproducts for their host. A new study published in Cell introduces a more accurate method to measure these fermentation products specifically short-chain fatty acids (SCFAs) which play key roles in human health.

The study revealed that over 90% of fatty acids produced by gut microbes are absorbed and used by the body with less than 10% excreted. Interestingly the total amount of fatty acids didn’t vary with microbial species composition only their type did. Ultimately the biggest factor influencing fatty acid production was diet emphasizing the impact of food choices on gut-driven energy metabolism.

In the oxygen-free environment of the large intestine microbes rely on fermentation to break down undigested food. When they ferment complex carbohydrates such as those found in oatmeal starchy vegetables and beans they produce short-chain fatty acids (SCFAs) like acetate propionate and butyrate as byproducts. These SCFAs are then absorbed by the body and used as an energy source when combined with oxygen.

Although these fatty acids play key roles in regulating digestion metabolism and immune function the gut microbiome remains highly complex and many aspects of its function are still unclear. According to Cremer accurately measuring SCFA levels is a vital step toward unraveling the connections between gut microbes and overall human health.

To arrive at their estimates the researchers first measured how efficiently gut microbes ferment carbohydrates in lab conditions. By tracking the growth and metabolism of key microbial species they calculated how much carbohydrate the microbes consumed and the amount of short-chain fatty acids they produced. They then combined this data with dietary information to estimate how much of these fermentation products are generated daily in the human gut.

To assess dietary variation the team drew from a range of nutrition studies including a UK-based reference study from the 1970s and recent U.S. dietary data from the National Institutes of Health. These were compared to the diet of the Hadza peoplea hunter-gatherer group in Tanzania whose eating habits reflect those of early humans providing insights into how different diets impact fermentation product output.

The team also validated their model using mice finding that mice obtain at least 20% of their daily energy from these microbial byproducts much more than humans. While mice remain a useful model in gut microbiome research the authors emphasize that this difference should be considered when translating findings to human health.

According to Cremer the newly developed quantification system will open the door to exploring new scientific questions. His team is now focused on investigating how gut microbes metabolize proteins and what effects this process has on human health.

Source: https://humsci.stanford.edu/feature/energy-supplied-gut-microbiome-depends-diet