Can your gut microbiome affect your cholesterol?

Gut bacteria convert bile acids, substances the liver makes from cholesterol. Through this conversion, the bacteria indirectly influence how the liver produces and excretes cholesterol. Disruptions in this system are associated with higher cholesterol levels and a greater risk of cardiovascular disease.

A key role is played by the enzyme bile salt hydrolase, which certain gut bacteria possess. Bacteria with this enzyme prevent bile acids from being lost through the stool. Less loss means the liver needs to convert less new cholesterol into bile acids, causing blood cholesterol to rise. On the other hand, there are also bacteria with the opposite effect: in a large observational study of more than 1,400 participants, Oscillibacter bacteria were found to be associated with lower cholesterol levels. In the lab, these bacteria proved capable of actively breaking down cholesterol. Whether this also directly reduces the risk of heart disease has not yet been proven.

Diet acts as an important intermediary. Gut bacteria ferment fibres into short-chain fatty acids. With low fibre intake, as in a typical Western diet, the gut microbiome changes in a way that is associated with higher LDL cholesterol and triglyceride levels. Eating more fibre can partly reverse this, although the causal evidence for this is not yet fully conclusive.

There are also supplements that attempt to influence cholesterol via the gut microbiome. Berberine, a plant-based substance at 500 mg per day, modifies the gut microbiome and inhibits genes involved in cholesterol absorption. However, the evidence in humans is still limited and long-term safety has not been sufficiently studied. Pu-erh tea contains a substance that, in mice and in a small human study, modified the gut microbiome and thereby lowered cholesterol levels. These are interesting findings, but not yet a basis for concrete recommendations.