Gut Health Foods: What the Evidence Supports (and What's Hype)

“Gut health” is everywhere, from supermarket shelves to social media. Some of it is backed by good evidence. Some of it is marketing. The encouraging part is that the foods with the strongest evidence are ordinary, affordable and already in most kitchens.

This guide covers the foods that are good for gut health according to UK health bodies and peer-reviewed research, and where the claims get ahead of the science.

Why fibre comes first

Most of the bacteria in your gut live in the large intestine, and fibre is a large part of what they eat. The British Dietetic Association (BDA) says fibre is essential for your gut to work normally, and that eating a range of fibre can improve the diversity of your gut bacteria and help with constipation.

The benefits go beyond digestion. A large set of reviews published in The Lancet in 2019, pooling data from around 185 studies and 58 trials, found that people who ate the most fibre had lower rates of heart disease, stroke, type 2 diabetes and bowel cancer than those who ate the least. The greatest benefits were seen at around 25g to 29g a day or more.

The NHS recommends 30g a day for adults. The BDA says UK adults average around 18g, so most of us have room to improve. Our guide to how much fibre you need a day shows what 30g looks like on a plate.

Foods with good evidence

Wholegrains

Oats, wholemeal bread, brown rice, wholewheat pasta, barley and higher-fibre breakfast cereals are some of the easiest ways to raise your fibre. The NHS lists wholemeal bread, brown rice and oats among its fibre sources for good digestion, and the Lancet reviews found similar benefits for wholegrain intake as for fibre.

Beans, lentils and chickpeas

Pulses are rich in fibre and cheap. A tin of chickpeas, lentils or mixed beans stirred into a soup, stew, curry or salad adds several grams in one go. They can cause wind at first, so add them gradually.

Fruit and vegetables, in variety

Different plants contain different kinds of fibre, and variety seems to matter. In the American Gut Project, a large citizen-science study of gut bacteria, people who ate more than 30 different types of plant a week had more diverse gut bacteria than those who ate 10 or fewer. That was an observational finding, so it shows an association rather than cause and effect, but it fits with the BDA's advice to eat a range of fibre. Rotating your vegetables, adding a handful of frozen berries or mixing different beans is an easy way to get more variety.

Nuts and seeds

A small handful of nuts, or a spoonful of linseeds, chia or pumpkin seeds on porridge or yoghurt, adds fibre and healthy fats. The NHS suggests unsalted nuts or seeds as a higher-fibre snack.

Fermented foods: promising, not proven

Yoghurt, kefir, sauerkraut, kimchi and kombucha contain live microbes. A 2021 Stanford study published in Cell randomly assigned 36 healthy adults to eat either more fermented foods or more fibre over several weeks. The fermented food group saw an increase in the diversity of their gut bacteria and a fall in several markers of inflammation.

It's an interesting result, but it was a small study, and the BDA notes that foods like kefir and kombucha aren't classed as probiotics because of a lack of scientific evidence. If you enjoy fermented foods, they can be part of a healthy diet. They aren't essential, and they don't replace fibre.

Where the hype runs ahead

Probiotic supplements

The NHS says there's some evidence probiotics may help in some cases, such as easing some symptoms of IBS, but little evidence for many of the health claims made about them. Probiotics are generally classed as food rather than medicine, so they don't go through the same testing. If you want to try one for IBS or constipation, the BDA suggests a four-week trial: if it doesn't help, try another or stop. NICE similarly advises people with IBS who try a probiotic to give it at least four weeks.

“Gut health” products

Many snack bars, drinks and powders carry gut-friendly claims. Some are a reasonable source of fibre, but plenty are ultra-processed and expensive for what they contain. Checking the fibre per serving on the label tells you more than the front of the pack. A bowl of oats with a sliced banana will usually beat a gut health bar on fibre and price.

Detoxes and cleanses

Your gut and liver don't need a juice cleanse to do their job. A cleanse that cuts out solid food also cuts out most of the fibre your gut bacteria rely on.

How to improve gut health without overhauling your diet

• Make one swap at a time: white bread to wholemeal, or white rice to brown.
• Add, don't subtract: a tin of beans in the bolognese, seeds on breakfast, an extra vegetable at dinner.
• Vary your plants: buy a different vegetable or fruit each week.
• Go gradually: the BDA advises increasing fibre slowly to avoid bloating and wind.
• Drink enough: the BDA notes fibre draws water into the bowel, and the NHS suggests a glass of water with every meal.
• Cut back on greasy fried food: the NHS says fatty foods are harder to digest and can cause stomach pain and heartburn.

If high-fibre foods make you feel worse

Not every gut responds the same way. The NHS notes that some people find cereals and grains bring on bloating or IBS symptoms, and suggests getting fibre from fruit and vegetables instead. If you have IBS, the type of fibre matters, and some healthy foods, such as onion, garlic, beans and certain fruits, are common triggers. Our guides to IBS trigger foods and bloating after eating explain how to work out which foods suit you.

Knowing where you stand

Most people have no idea how much fibre they eat, which makes it hard to know where to start. GutBox counts your fibre and your ultra-processed foods as you log meals by photo, voice or barcode, and suggests foods that could close the day's fibre gap. If a food seems to disagree with you, it lines your meals up against your symptoms so you can see the pattern. It's free to download.