Gut microbiota: what to eat to care for it

What is the gut microbiota and why does its diversity matter?

The gut microbiota is the community of microorganisms that lives in the digestive tract, mostly in the colon. Many different species live together there. Diversity describes how many types live together. On its own, it cannot tell you how healthy you are.

The American Gut project observed that people who ate more than 30 different plants a week had a more diverse microbiota than those who ate fewer than 10 [2]. This is an association, not proof that reaching 30 will change your health. You can start by adding variety to what already agrees with you.

If what bothers you is mostly your stomach, with heartburn or heaviness after eating, start with the gastritis diet, the general guide from our digestive team.

Which foods provide fibre for the microbiota?

Many bacteria in the colon make use of the fibre we do not absorb. Some fibres act as prebiotics. The consensus of the scientific association ISAPP reserves that term for substrates that are used selectively by microorganisms and linked to a health benefit [3].

The European authority EFSA considers 25 g of fibre a day adequate for normal bowel transit in adults [1]. This is a general reference, not a dose prescribed to change the microbiota. If you usually eat little fibre, increase it gradually and watch how you tolerate it.

• Vegetables and fruit. Combine different seasonal options, such as leek, artichoke, apple and pear.
• Pulses and wholegrains. Try lentils, chickpeas, oats or wholemeal rye bread.
• Resistant starch. Potato or rice that has been cooked and cooled provides starch that can be fermented in the colon.

How fermented foods fit in

Fermented foods are made through the controlled growth of microorganisms. This is how the ISAPP consensus defines them [4]. Plain yoghurt, kefir or some fermented vegetables can add variety to your meals.

Not all of them still contain live microorganisms when you eat them. Sourdough bread, for example, is baked. Nor is every fermented food a probiotic. That name requires a demonstrated benefit for specific microorganisms [4]. If you like them and they agree with you, you can include them without setting yourself a required frequency.

Are probiotic supplements necessary?

This is a common question in consultation. The World Gastroenterology Organisation guideline explains that possible effects depend on the strain and on the situation studied [5]. For that reason, we do not recommend choosing a product only for the number of bacteria it advertises.

If you eat a varied diet and have no symptoms, you do not need to take them as a matter of routine. There is also not enough evidence to recommend probiotics for bloating. If you have a diagnosed digestive problem, such as irritable bowel syndrome, talk to your doctor or registered dietitian-nutritionist. We do not recommend strains by default. If there is a specific medical indication, your doctor or your registered dietitian-nutritionist will set it.

What does dysbiosis mean, and can a commercial test detect it?

Dysbiosis is a term for changes in the microbial community. On its own, it is not the same as a disease, and it does not explain every case of bloating. There is still no single “normal” microbiota pattern against which to compare everyone [6].

The international consensus on microbiota analysis does not support using a “dysbiosis index” to diagnose or to prescribe a diet [6]. A commercial stool test also does not capture the whole gut. If you have persistent symptoms, your doctor will decide which tests make sense. Avoid cutting out foods because of a laboratory score.

Your eating adapts to your symptoms and your life, not to a test score.

When ultra-processed foods crowd out plant variety

When ultra-processed foods take up much of the plate, there tends to be less room for pulses, fruit and vegetables. Those foods provide the microbiota with different kinds of fibre. Smoking is not a strategy for looking after it either. There is no safe amount of alcohol for health (WHO): the less, the better; and none during pregnancy, breastfeeding, childhood, if you are going to drive or if your medication does not allow it.

The gut-brain axis describes two-way communication. A review of studies in people found associations between the microbiota and depression, without showing that changing it treats that condition [7]. If low mood persists or affects your daily life, ask for a medical or psychological assessment.

How long does the microbiota take to respond to dietary changes?

In intensive dietary interventions, changes in microbial composition have been observed within 24 to 48 hours [8]. The review that brings those studies together also indicates that many changes are temporary. We still do not know how long a diet pattern must be kept up to produce a lasting change [8].

That is why we suggest adjustments you can sustain. Adding one pulse you tolerate and one new vegetable to the weekly shop is worth more than a week of difficult rules.

What do we know about so-called “leaky gut”?

Intestinal permeability is a property of the gut barrier. It can be altered in some diseases, but having gas or bloating does not show that the barrier is damaged. “Leaky gut” is not, on its own, an accepted medical diagnosis [9].

A clinical review warns that commercial tests and plans to “repair” it have no established usefulness for those symptoms [9]. If the discomfort continues, ask for a medical assessment before paying for tests or cutting out food groups.

What mistakes do we see in consultation?

• Raising fibre all at once can cause temporary gas. Go step by step and drink enough water.
• Staying on a low-FODMAP diet without setting an end date from the first day. The exclusion phase lasts 2 to 6 weeks and is followed by a guided reintroduction.
• Cutting out foods because of a stool test. First we review your symptoms and the relevant medical tests.
• Trying for one perfect week and giving up afterwards. The aim is to find changes that fit your routine.