The gut is increasingly called the body’s “second brain,” and for good reason: it’s home to trillions of bacteria that affect not just digestion but immunity, mood, and overall well-being. The good news is that supporting this microbiome doesn’t require a strict diet or expensive supplements — mostly it comes down to shaping an ordinary diet the right way.

Researchers are still working out exactly how the makeup of gut bacteria connects to specific health outcomes, and there’s no single formula for an “ideal microbiome.” Still, a handful of dietary principles are well established at this point and tend to hold up regardless of which particular bacterial species dominate any one person’s gut.

Fiber as the primary fuel

Beneficial gut bacteria feed mainly on fiber — specifically the portion that isn’t broken down in the small intestine and reaches the large intestine largely intact. There, bacteria ferment it and produce short-chain fatty acids, which are considered beneficial for the health of the gut lining. Fiber sources include vegetables, fruit, whole grains, legumes, nuts, and seeds. The more varied the plant foods in a diet, the more varied the microbiome tends to be, and a more diverse mix of bacterial species is generally associated with steadier digestion.

Fermented foods and live cultures

A separate category worth highlighting is fermented foods: yogurt, kefir, sauerkraut, kimchi, miso. Many of these contain live bacterial cultures that can temporarily add beneficial strains to the gut. Eating them regularly is a simple, accessible way to diversify gut flora, especially for anyone whose diet hasn’t included much of this kind of food before.

Prebiotics: food for the bacteria already there

Beyond foods with live cultures (probiotics), prebiotics matter too — compounds that feed the bacteria already living in the gut. Prebiotics show up in meaningful amounts in onions, garlic, Jerusalem artichokes, bananas, oats, and chicory. Combining probiotic and prebiotic foods in the diet tends to work better than either one alone.

What’s worth limiting

Heavily processed food that’s high in refined sugar and saturated fat but low in fiber is generally linked with a less diverse microbiome. Excessive intake of artificial sweeteners is sometimes mentioned as another factor that may nudge the balance of gut bacteria in a less favorable direction, though research on that is still evolving. A reasonable approach isn’t to cut such food out entirely, just to avoid making it the foundation of the diet.

Animal versus plant protein

Protein matters for the gut too, though less directly than fiber does. A diet where plant protein from legumes, nuts, and whole grains sits alongside animal protein tends to deliver more fiber overall than one built almost entirely around meat. That doesn’t mean meat and fish need to go — it’s more about not overlooking plant protein sources as another easy way to add fiber and variety to the plate.

Water, routine, and variety

Beyond specific foods, broader habits matter too: drinking enough water helps fiber do its job the way it’s supposed to, rather than causing discomfort. A regular eating pattern and a plate that consistently includes vegetables and fruit matter just as much as hunting for one “superfood” for gut health. Overall dietary variety appears to matter more for the microbiome than eating the same single healthy food every day.

Putting it into practice

A good starting point is small changes: add a serving of fermented vegetables or plain yogurt to an ordinary day, choose whole grains over refined ones for side dishes, and aim to eat as many different vegetables and fruits as possible over the course of a week rather than the same two or three. Anyone who hasn’t eaten much fiber before should increase it gradually — a sudden jump can cause temporary bloating while the microbiome adjusts to the new diet.