The gut-brain axis is a bidirectional communication system between the gastrointestinal tract and the brain, in which the vagus nerve and the gut microbiota play an important role. Among other things, gut bacteria produce neurotransmitters and short-chain fatty acids, which influence mood, cognitive function and inflammation in the body. A diet rich in fibre, vegetables, fruit and fermented products supports the favourable composition of the microbiota and the proper functioning of this axis. In contrast, disorders of the microbiota (dysbiosis) can promote inflammation, mental problems and neurodegenerative diseases.