Gut health foods: what to eat, what the evidence says and when to see a doctor

The short answer: the best gut health foods are high-fiber plant foods, such as beans, lentils, whole grains, fruit and vegetables, plus fermented foods with live cultures, such as yogurt, kefir, kimchi and sauerkraut. Fiber feeds your helpful gut bacteria, Harvard says. In a 2021 Stanford trial, a diet high in fermented foods raised gut microbe diversity and lowered 19 inflammatory proteins in the blood.

You don’t need special powders. Most of the foods below are cheap and easy to find.

What is gut health?

Gut health usually means how well your digestive system works, including the microbes that live in it. Cleveland Clinic says your gut holds trillions of microorganisms, including over a thousand species of bacteria, and up to 80% of your body’s immune cells. Together these microbes are called the gut microbiome. A wide variety of them is linked with resistance to harmful types, Cleveland Clinic says. Harvard’s Nutrition Source adds an honest caution: scientists are still in the early stages of understanding the microbiome’s role in health.

What foods are good for gut health?

The foods with the best support for gut health are those rich in fiber and those with live microbes. This table pulls from Harvard, Cleveland Clinic, the NHS and the Stanford trial, and says how strong the evidence is for each.

"Strong" here means fiber has well-established links with health. The NHS says eating plenty of fiber is associated with a lower risk of heart disease, stroke, type 2 diabetes and bowel cancer. "Early" and "promising" mean the gut-specific research is young or small.

How does fiber help gut health?

Fiber helps gut health by feeding the bacteria in your colon. Harvard’s Nutrition Source explains that these bacteria ferment fibers your body can’t digest and make short-chain fatty acids, which your body can use as a nutrient source. That’s why such fibers are called prebiotics: they feed your helpful microbes. Harvard adds that a low-fiber diet may reduce the amount of helpful bacteria.

Most people are short. The NHS recommends 30g of fiber a day, while most UK adults average about 20g. Beans and lentils are the quickest way to close the gap, and our guide to the best beans for protein lists the fiber in 15 of them. Our high-fiber foods list covers fruit, vegetables and grains.

Go slowly. Harvard warns that a sudden jump in prebiotic foods can cause gas and bloating, and that people with irritable bowel syndrome (IBS) should start with small amounts.

Are fermented foods good for gut health?

Fermented foods look good for gut health, based mainly on one small but careful trial. In 2021, Stanford researchers published a study in the journal Cell in which 36 healthy adults were randomly assigned to eat either a high-fermented-food diet or a high-fiber diet for 10 weeks.

• The foods: yogurt, kefir, fermented cottage cheese, kimchi and other fermented vegetables, vegetable brine drinks and kombucha.
• Fermented-food group: gut microbe diversity rose, 19 inflammatory proteins in the blood fell, including interleukin 6 (IL-6), and four types of immune cells showed less activation. Larger servings had stronger effects.
• High-fiber group: diversity stayed stable, and none of the 19 inflammatory proteins fell.

The researchers were careful about what this means. One of them called it a proof-of-concept study, and another said a longer trial might have given the microbes time to adapt to more fiber. Lower blood markers aren’t the same as less disease. So fermented foods are a sensible addition, and fiber still matters. If inflammation is your main interest, our anti-inflammatory diet guide covers the wider evidence.

Do probiotics work?

Some probiotics may help in some cases, but for most uses no one knows yet which ones work. The National Center for Complementary and Integrative Health (NCCIH) defines probiotics as live microorganisms meant to have health benefits, found in yogurt and other fermented foods, supplements and beauty products. It says that in most instances, we still don’t know which probiotics are helpful and which aren’t.

The NHS says there’s some evidence probiotics may ease some IBS symptoms, but little evidence for many of the health claims made about them. Both agencies raise the same problems with supplements:

• They’re sold as supplements or food, not medicines, so they don’t need FDA approval before they’re sold, NCCIH says.
• The label may not match what’s inside. Some products have contained microbes not listed on the label, and the NHS says you can’t be sure enough bacteria survive to reach your gut.
• They aren’t for everyone. People with a serious illness or a weakened immune system face greater risks and should talk to a doctor first.

Harvard says it’s still an open question whether a fairly healthy person gains anything from probiotics beyond a fiber-rich diet. Food is the simpler place to start.

What foods are bad for gut health?

Diets high in sugar, saturated fat and processed foods are the main ones that may harm gut health. Cleveland Clinic says a diet high in sugar and saturated fats tends to favor the less helpful microbes, and that processed and convenience foods lack fiber and often contain additives and preservatives. It also names alcohol and tobacco smoke. Harvard points to low-fiber eating.

Some medicines play a part too. Cleveland Clinic says antibiotics can kill good bacteria along with the bad, and that acid blockers can shift the gut’s balance. Harvard links prolonged antibiotic use to an imbalance in gut microbes. These medicines are often needed, so keep taking them as prescribed and ask your doctor if you have concerns.

For bloating, the NHS suggests going easy on fizzy drinks, alcohol and caffeine, and not eating large meals late at night.

What are the signs of poor gut health?

Gas, bloating and changes in your poo are the usual signs people notice, and they often come from food. But some gut symptoms need a doctor, whatever you eat. The NHS lists these possible bowel cancer symptoms, and says they’re common and often caused by something else, so get them checked:

• A change in your poo that isn’t usual for you, such as softer poo, diarrhea or constipation, or going more or less often
• Blood in your poo, which may look red or black, or bleeding from your bottom
• Often feeling you need to poo, even just after going
• Tummy pain, bloating or a lump in your tummy
• Losing weight without trying, or feeling very tired or short of breath

Get urgent help the same day if your poo is black or dark red, you have bloody diarrhea, or bloating comes with vomiting, stomach pain, a fever, or you can’t pee, poo or pass gas. Call 911 or your local emergency number for bleeding from your bottom that won’t stop, a lot of blood or large clots, a sudden severe stomach ache with a swollen stomach, or vomiting blood or what looks like coffee grounds. These steps come from the NHS.

How can I improve my gut health naturally?

You can improve your gut health by eating more fiber, adding a fermented food and cutting back on processed food, one step at a time. Start this week:

• Add one bean meal. The NHS suggests adding beans, lentils or chickpeas to stews, curries and salads.
• Swap one grain. Choose oats, barley or whole-wheat bread over refined versions.
• Have one fermented food a day. Plain yogurt or kefir with live cultures, or a spoonful of kimchi or sauerkraut.
• Eat more kinds of plants. Different fruits, vegetables, nuts and grains bring different fibers.
• Build up slowly and drink plenty of water, as the NHS suggests for bloating.

If you have IBS, Crohn’s disease, colitis or another gut condition, check big diet changes with your doctor first. Our guide to what a balanced diet looks like shows how these foods fit a whole day, our free 7-day meal plan gives you a week of easy meals, and The Banana Book below lists the fiber in every recipe.

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Quick questions

Is yogurt good for gut health?

Yogurt with live cultures can be good for gut health. Harvard lists yogurt with live active cultures among fermented foods with helpful microbes, and yogurt was part of the 2021 Stanford diet that raised gut microbe diversity. Check the label for live cultures, and choose plain yogurt to avoid added sugar, which Cleveland Clinic links to less helpful microbes.

Is sourdough good for gut health?

Sourdough is fermented, but Harvard notes it doesn’t contain live microorganisms, so it isn’t a live-culture food like yogurt or kimchi. It can still help in another way. A whole-grain sourdough brings fiber, and Harvard says fiber feeds your helpful gut bacteria. Check the flour on the label if fiber is your goal.

Is kimchi good for gut health?

Kimchi can be good for gut health. Harvard lists it among fermented foods, and kimchi was one of the foods in the 2021 Stanford trial, where a high-fermented-food diet raised gut microbe diversity and lowered inflammatory markers. Harvard notes that heat-treated fermented vegetables may not contain live microbes. It was a small trial, so the evidence is promising, not settled.

Are probiotics good for you?

Probiotics appear safe for most people, the NHS says, but there’s little evidence for many health claims made about them. NCCIH says we mostly don’t know which probiotics help. Supplements don’t need FDA approval, and labels may not match the contents. People with a serious illness or a weakened immune system should talk to a doctor first.

Are bananas good for gut health?

Bananas are good for gut health. Harvard’s Nutrition Source lists bananas among foods with prebiotic fibers, which feed helpful gut bacteria, alongside garlic, onions, leeks, asparagus and whole grains. A medium banana has about 3g of fiber by USDA figures. Pair it with yogurt or oats for more fiber and a fermented food in one snack.

What are the worst foods for gut health?

The foods most linked with poor gut health are those high in sugar and saturated fat, and processed foods low in fiber, according to Cleveland Clinic. It also names alcohol and tobacco smoke. Harvard points to low-fiber diets in general. Nothing has to be banned. Making more of your meals from beans, whole grains and plants does the most good.

This article is general information, not medical advice. If you have IBS, inflammatory bowel disease, a weakened immune system or another health condition, talk to your doctor before taking probiotics or making big changes to your diet. Keep taking any medicine as prescribed. See a doctor for blood in your poo, a lasting change in your bowel habits or weight loss you can’t explain.

Sources

• Harvard T.H. Chan School of Public Health, The Nutrition Source. The Microbiome
• Cleveland Clinic. Gut Microbiome
• Stanford Medicine. Fermented-food diet increases microbiome diversity, decreases inflammatory proteins, study finds (2021)
• Wastyk HC et al. Gut-microbiota-targeted diets modulate human immune status. Cell, 2021
• NCCIH. Probiotics: What You Need To Know
• NHS. Probiotics
• NHS. How to get more fibre into your diet
• NHS. Bowel cancer symptoms
• NHS. Bloating