The answer is… not a lot. Well, actually, a bit. Look, it’s complicated. There’s a new study out that tries to answer this question and I’ve written about it for Nature News. Here’s the summary, but do read the full piece – the really interesting thing here is the potential for future experiments that will actually be able to test some of the grandiose claims that adorn yoghurt packets.
Many yoghurts are loaded with live bacteria, and labelled with claims that consuming these microorganisms can be good for your health. But a study published today shows that such yoghurts have only subtle effects on the bacteria already in the gut and do not replace them.
Nathan McNulty, a microbiologist at Washington University in St Louis, Missouri, recruited seven pairs of identical twins, and asked one in each pair to eat twice-daily servings of a popular yoghurt brand containing five strains of bacteria.
By sequencing bacterial DNA in the twins’ stool samples, the team showed that the yoghurt microbes neither took up residence in the volunteers’ guts, nor affected the make-up of the local bacterial communities.
McNulty also fed the five bacterial strains from the yoghurt to ‘gnotobiotic’ mice — animals raised so that the only microorganisms that their guts contain are 15 species found in humans.
As with the twins, the yoghurt bacteria did not change the composition of the rodents’ resident communities. However, the activity of genes that allow the native bacteria to break down carbohydrates did increase.
Meanwhile, if you’re interesting in the bacteria in our guts and bodies, have a look at this introductory slideshow:
Image by Coda.