Your gut is home to trillions of bacteria and other microbes, collectively called the gut microbiome. They break down fiber your own body can't, produce vitamins and short-chain fatty acids, and help train your immune system. A more diverse microbiome is generally associated with better health, while low diversity is linked to conditions like obesity and inflammatory bowel disease.
The single biggest lever you control is fiber. Microbes ferment plant fiber into compounds that nourish your gut lining and calm inflammation. Diets rich in varied plants, whole grains, beans, and fermented foods tend to support a healthier microbiome, while diets high in ultra-processed foods tend not to. You're not just feeding yourself — you're feeding them.