Can exercise improve your gut microbiome?

Moderate endurance exercise increases the diversity of bacterial species in your gut and promotes beneficial bacteria that produce short-chain fatty acids. These fatty acids are important for the gut lining and the immune system. This effect has been demonstrated in multiple studies, although the precise magnitude varies from person to person and by type of exercise.

A six-week endurance training study in people who had previously been largely sedentary showed that the amount of short-chain fatty acids in the stool increased. But only in people with a healthy weight, not in people with excess weight. And as soon as they stopped training, the changes in the gut microbiome largely disappeared again. This indicates that staying consistent with exercise is necessary to maintain the effect.

More is not always better: prolonged intensive endurance exercise, such as that performed by elite athletes, can actually make the gut lining more permeable and thereby trigger inflammation. In well over half of the studies examined, this negative effect was found with intensive training. Moderate exercise therefore appears to offer a sweeter balance than high-level performance.

Combinations of endurance training and strength training are associated with greater bacterial diversity in the gut and a lower risk of metabolic conditions such as type 2 diabetes. This association has been observed, but its causality is less certain than for endurance exercise alone.

Furthermore, there are early indications that exercise may also play a role in mood and even in defence against tumours, via the gut microbiome. For instance, gut bacteria produce a substance during exercise that makes immune cells more active, which had antitumour effects in mouse research. This is still laboratory research in mice; its significance for humans remains unclear. The same applies to a possible beneficial effect on depression via the gut-brain axis: biologically plausible, but the clinical evidence is still thin.