Then there are the countless probiotic yoghurts and drinks marketed under the claim that consuming their “friendly” microorganisms can be good for your health. A study published last year suggests their effects might be subtle only. Comparing DNA stool samples from one identical twin who ate probiotic yoghurt with one who did not showed little difference in the make-up of their gut bacteria, but studies in mice showed probiotic yoghurt did affect the activity of genes that allow gut bacteria to break down carbohydrates.
Scientists do not know yet whether some people might respond better to probiotics and dietary changes than others. The “big promise of the future”, says Ehrlich, is that simple dietary changes could manipulate the balance of our gut bugs before diseases develop. When that time will come is impossible to predict, he says, but, at least the Human Microbiome Project and MetaHIT scientists are beginning to know which questions to ask.
Until that time comes, the 69-year-old researcher has perhaps an unconventional suggestion for younger people. If he were 18 again, he says he would deep-freeze a stool sample at a biobank, in case he ever needed a faecal transplant. See, I told you this story would gross you out.