The gut microbiome is a community of tens of trillions of microorganisms (10¹³–10¹⁴ cells) that live mainly in the large intestine. This is the highest density of microbes in the body: 300–1000 species, though about 99% belong to just 30–40 of them.
Two types of bacteria predominate — Bacteroidota and Firmicutes (Bacillota). The microbiome is not a passive "passenger": it digests what humans cannot, trains the immune system and takes part in metabolism.
What the bacteria do
The microbiome's main "job" is fermenting dietary fibre, which the body itself cannot digest. This produces short-chain fatty acids (SCFAs): butyrate, propionate and acetate. Butyrate serves as the main fuel for the cells lining the large intestine. In addition, the bacteria synthesize vitamin K and some B vitamins, support the intestinal barrier and "train" the immune system.
Dysbiosis and disease
A disturbed microbiome composition (dysbiosis) is linked to obesity, inflammatory bowel disease, metabolic syndrome and an increased risk of type 2 diabetes. It is important to be honest: most of these links are so far only correlational — scientists are still working out where the cause lies and where the effect.
How to influence the microbiome
Diet has the strongest effect on the microbiome: varied fibre (vegetables, legumes, whole grains) and fermented foods support beneficial bacteria. The composition stabilizes by about age 2 and gradually changes with age. The effect of probiotic supplements depends on the strain and the situation and is not yet universal, so diet remains the foundation.
Calculate using this marker
Calculators where Gut microbiome is used directly:
Frequently asked questions
What are short-chain fatty acids?
These are butyrate, propionate and acetate — produced by gut bacteria from fibre. Butyrate feeds the cells of the large intestine, and SCFAs overall support the barrier and metabolism.
Do probiotics help?
Sometimes — the effect depends on the specific strain and situation and is not universal. The most reliable influence on the microbiome comes from varied fibre and fermented foods in the diet.