It’s not hard to stumble across any number of articles and papers proclaiming the next wonder food to improve your gut health. As scientists increasingly discover the central role that gut bacteria play in our overall health, it’s tempting to latch on to these promises to try to revitalise everything from your weight to mental wellbeing. But the science has a way to go before we know exactly what nutrition is best for your gut. BBC Future spoke to leading gut health and microbiome researchers to sift fact from fiction on gut health “wonder foods”, probiotics, prebiotics and what changes to your diet could genuinely boost your gut health.

Probiotics

Eating as varied a diet as possible is probably the best way to keep a gut biome healthy. That might seem like a logical plan – more healthy bacteria, healthier gut. But of course, that’s just the start. It’s not just about quantity of those helpful bacterial strains, it’s about diversity. “There are many thousands of different types of bacteria found in people’s microbiomes. Each individual person might have 150-250 types in their gut,” says Whelan.

Verdict: Adding a few strains of bacteria to your microbiome through taking a probiotic probably won’t boost your gut health diversity all that much.

Prebiotics

Just one letter different, prebiotics are a source of food for probiotic bacteria to live off. These molecules are often indigestible to humans, so pass straight through the gut to where the bacteria are. Microbiome diversity is probably not achievable by swallowing a whole range of supplements. While taking a probiotic may be like planting a seed, taking a prebiotic is like nurturing it by giving it nourishment. But again, this approach comes up against the same limitations as taking a probiotic alone.

Verdict: “Prebiotics do not increase the diversity of the microbiome,” says Whelan. “They will increase specific bacteria, but they won’t increase the number of different types of bacteria.”

Mixing it up

There are ways to improve diversity by focusing on the foods you eat. Scientists say variety is key. “Dietary diversity is about challenging the concept of constantly eating the same thing,” says Whelan. “For example, if you have fish regularly, make sure it isn’t always salmon. Make sure you have wholegrains regularly, but not just wholegrain bread.”

Verdict: Evidence for the efficacy of specific foods is always questionable, but eating a varied and diverse diet of healthy foods is likely to lead to an equally diverse and healthy microbiome.

Fermented foods

Studies are also pointing to possible benefits from fermented foods such as Kimchi, kombucha and kefir. These foods, which have been made traditionally for thousands of years, have been studied in the field of “psychobiotics”, which is when ingesting bacteria of a particular type has a positive mental health effect. Some studies have shown that people taking fermented milk products had lower levels of cortisol, a stress marker, in their blood compared to a placebo control group, and also had a more diverse microbiome. While these results are promising, studies such as this are often small.

Verdict: Fermented foods may help boost your microbiome diversity – but the science hasn’t up with this craze yet to say with certainty either way.

Write some sentences using the … words and phrases

1. What is a health food craze that you know?
2. What is a traditional healthy food?
3. Are older or younger people in your country healthier?
4. Why do people believe food crazes/fads so easily?
5. Name other fermented products
6. How do you combat stress?