The gut microbiome is a vast ecosystem of microorganisms that help digest fibre, produce short-chain fatty acids, train the immune system, and manufacture vitamins including K2 and some B vitamins. Dysbiosis refers to an unfavourable shift in this ecosystem — reduced diversity, overgrowth of opportunistic species, or depletion of beneficial ones.
A note on evidence quality: gut microbiome research is one of the most rapidly advancing — and most overhyped — areas of nutrition science. Association studies link dysbiosis with conditions ranging from IBS to obesity to depression, but causality is rarely established. Many commercial “microbiome tests” and targeted probiotic products exceed what the current evidence supports.
What we do know with reasonable confidence: dietary fibre diversity is the most reliable driver of microbiome diversity. People eating 30+ different plant foods per week have measurably richer gut ecosystems than those eating fewer. Antibiotic use, ultra-processed food patterns, and very low fibre intakes are consistently associated with reduced diversity.
Practical foundations: eat a wide variety of vegetables, legumes, whole grains, fruit, nuts, and seeds; fermented foods (probiotics and prebiotics) add beneficial organisms and substrates. Avoid unnecessary antibiotics. Be sceptical of expensive probiotic supplements making sweeping health claims.