Gut microbiome

Around 38 trillion bacteria live in your gut – roughly as many as there are cells in your body. This community is called the microbiome, and it works for you: it breaks down fibre that your small intestine can't digest, produces vitamin K and some B vitamins, trains the immune system and protects the gut wall against pathogens. In the process, fibre is turned into short-chain fatty acids such as butyrate, which nourish the gut lining, dampen inflammation and stimulate satiety hormones.

What does this have to do with weight? People who are severely overweight have, on average, a less diverse microbiome. In mice, the link is even causal: if they are given the gut flora of overweight animals, they gain weight. In humans, the research is younger and more cautious – what is clear is that the microbiome influences how much energy is extracted from food, how stable blood sugar remains and how satiety signals get through. It isn't a miracle cure: probiotic capsules (supplements containing live bacteria) for weight loss have not yet shown a reliable effect in studies.

What has been shown to benefit the microbiome is refreshingly unspectacular: a variety of plants – vegetables, fruit, wholegrains, pulses, nuts, herbs. In the American Gut Project, people who ate more than 30 different plant species a week had a much more diverse gut flora than those who ate fewer than ten. Add to that fermented foods such as yoghurt, kefir and sauerkraut, little ultra-processed food and sugar, exercise, sleep – and antibiotics only when they're really needed, because they also wipe out the beneficial bacteria.

In children, the microbiome develops during the first years of life: birth, breastfeeding, varied weaning foods, playing outdoors and contact with animals all shape it. So a colourful family kitchen is also good gut care – and digestive problems after switching to more fibre usually settle down after two to three weeks, once the bacteria have adapted.