There are many claims made about gut health. We are told that having the right gut bugs will make us slim, boost our immune system, even cure depression. But for all the health claims you may read, there is still a lot to discover about what gut bugs can and cannot do.

How to care for your gut’s microbes

Even though our internal world is still largely a mystery, we do have a good idea of how to keep the gut microbiome as diverse and healthy as possible. One way is through the foods we eat, and those we avoid.

The most important step is to eat a plant-rich, whole food diet, says nutrition scientist and gut health expert Dr Joanna McMillan. This includes fruit, vegetables, wholegrains, nuts, seeds and the oils made from them.

At the same time, limit or avoid ultra-processed foods. These are foods made from ingredients that are already heavily processed so that the resulting food product is far removed from the original plant or animal food.

Why the focus on plant foods?

There are two groups of plant compounds that are key for gut health and fuelling your microbiome, says Dr McMillan – fibre and polyphenols.

All the different types of fibre are carbohydrates that our digestive enzymes can’t break down, so they arrive intact to the large intestine (colon). Many of these types of fibre are fermented by the gut microbiome, explains Dr McMillan.

The gut microbiome works hard to support us, too. It produces substances that help prevent the growth of harmful bacteria, reduce inflammation in the gut and the rest of the body, provide fuel for the cells lining the gut to keep them healthy, and support the immune system.

The best sources of fibre? All plant foods, but particularly legumes and wholegrains.

Polyphenols are compounds found widely in plant foods, says Dr McMillan, and like fibre, they also promote a healthy, diverse microbiome.

“Your friendly gut bugs convert these polyphenols into more bioactive compounds with diverse health benefits throughout the body,” she explains.

Recent research has shown polyphenols have prebiotic effects, promoting the growth of beneficial bacteria in the gut. They are also anti-inflammatory and prevent the growth of potentially harmful bacteria.

The best sources of polyphenols?

Extra virgin olive oil has more than 30 polyphenols, says Dr McMillan. Other good sources of polyphenols are colourful fruits and vegetables, and nuts and seeds.

Do you always but the same fruit and vegetable?

Sticking to the same fruit and vegetables every day is likely to decrease the range of your gut microbiota.

“If you want to increase gut microbe diversity, you should try and have 30 different plant-based foods a week,” says dietitian and gut health expert Dr Megan Rossi.

Sounds impossible? Gradually introduce foods you may not normally eat, such as barley, quinoa, chickpeas, eggplant, Brazil nuts, pumpkin and chia seeds, asparagus, and kale. For example, you can base a salad on barley, add some nuts and seeds, three types of vegetables, a little dried fruit, and a dressing based on olive oil. That will give you up to eight different plant foods.