If you've been in a grocery store lately, you're probably well aware that probiotics are the latest health craze since the recent kale fiasco, but once you wade through all the hype, do these expensive, bacteria-laden foods and drinks actually do anything? According to a team of researchers from Denmark, the answer is a big fat no.  

The team looked at test data gathered on seven probiotic products and found no evidence that they changed the mix of faecal bacteria in healthy adults. A larger sample size is needed to confirm once and for all if these products have any kind of influence on our inner microbiome, but these initial results are pretty telling. 

Even if you don't take probiotics, you've likely heard quite a bit about them, but for the uninitiated, they're basically living microorganisms that are designed to encourage the growth of healthy gut bacteria and aid digestive system function. We produce our own probiotics internally, but plenty of foods and drinks claim to boost their numbers.

Scientists from the Novo Nordisk Foundation Centre for Basic Metabolic Research at the University of Copenhagen whittled down over 1,000 studies to identify seven probiotic products to test, which you can do some background reading on here: Beneficial Microbes (1, 2), the British Journal of Nutrition (1), PeerJ (1), the Journal of Nutrition, Health and Aging (1), Diabetes Care (1) and the Journal of Nutrition (1).

In the seven studies analysed, the numbers of participants varied between 21 and 81, with ages ranging from 19 to 88, and they involved probiotic biscuits, drinks, sachets, or capsules administered for periods of 21 to 42 days.

In only one of these studies did the team find a difference in gut bacteria between those participants who were taking probiotic supplements and those who weren't, and the link between the two was slight.

"According to our systematic review, no convincing evidence exists for consistent effects of examined probiotics on faecal microbiota composition in healthy adults, despite probiotic products being consumed to a large extent by the general population," said team member Nadja Buus Kristensen.

But the case isn't entirely closed just yet, because the sample sizes in each of these studies were very small. And as the researchers point out, someone needs to conduct a more wide-reaching study to figure out what exactly is going on here.

"To explore the potential of probiotics to contribute to disease prevention in healthy people, there is a major need for much larger, carefully designed and carefully conducted clinical trials," said one of the team, Oluf Borbye Pedersen.

There is some evidence - like this 2014 study and this 2015 study - that probiotic food and drink can actually help improve digestive bacteria and health for those with obesity or diabetes, and research has tentatively suggested that they could shorten the effects of diarrhea in children.

But it's looking more and more unlikely that by spending a significant chunk of cash on fancy probiotics products, you're actually having any discernible effects on your health. Just go for a run instead.