Can your gut microbiome control your appetite and hunger?

Gut bacteria can actively influence your feelings of hunger and fullness. They do this through several pathways: they stimulate specialised intestinal cells that secrete hormones, and those hormones activate the vagus nerve, the major communication line between your gut and your brain. That nerve plays a key role in what you want to eat and how much. This pattern has been found repeatedly in human and animal research.

A concrete mechanism involves the short-chain fatty acids that gut bacteria produce when they ferment fibre, including acetate, propionate and butyrate. These substances appear to dampen your energy balance and appetite. However, a caveat applies here: the most convincing results come from animal and laboratory studies. In humans, the effect has barely been tested in controlled trials, so we do not yet know how large that effect is in practice.

That the gut microbiome also partly determines how much energy you extract from food became clear from experiments in which gut microbiota from obese humans or animals were transferred to germ-free test animals: those animals subsequently stored more fat. People with obesity have, on average, a different gut microbiome composition than people with a healthy weight, which plays a role in fat storage and insulin sensitivity.

Dietary fibre remains the most concrete lever you can use yourself for now. The gut microbiome is the mediator that converts fibre into signals that regulate your appetite. Eating more fibre changes the composition of your gut microbiome and appears, through that pathway, to have a beneficial effect on your metabolic health. For more high-tech options, such as returning your own gut microbiota after weight loss to limit weight regain, the first results are interesting but the research is still too early-stage for practical application.