“82% of people with digestive discomfort said they felt better after eating Activia,”says a recent poster for the probiotic. So if you have tum trouble should you get down the shops and buy it?

 
Not on the evidence presented. The advertisers cite a study by Denis Guyonnet in the Journal of Digestive Diseases in support of the claim. This took an initial group of 371 adults and divided them into three groups – 144 who ate one pot of the stuff, 147 who took 2, and a control group of 69 people who followed their usual diet. The conclusion was that 82.5 per cent of the one-pot eaters and 84.3 or the two-pot eaters reported improved digestive comfort, compared with 2.9 per cent of the controls.
 
The company says the article was peer-reviewed. Dr Guyonnet is an employee of Danone, the company that makes Activia, as was one of his collaborators. The research was carried out in two centres in England.
 
Leave aside some of the little statistical quirks of the study: for example the reporting of a finding for a group of just 69 people to one-tenth of a percentage point. What does this study prove?
 
Practically nothing. Stomach pains come and go. If you give someone a soothing pot of something and ask them a bit later if they feel better probably they will say “yes”. This may be to be obliging, or because there has been a placebo effect. Ordinary yoghurt might do the trick equally well. The results might have been more persuasive if, indeed, the control group had been given ordinary yoghurt and the trial had been blinded.
 
As it is, the effect claimed was stronger in many measures for those who had a single pot than for those who had two. And the difference between those who consumed Activia and those who stuck to their normal diet appears to be exaggerated. In the measure of "general digestive discomfort",  84.0 per cent of those eating a single pot a day reported an improvement, while 78.9 per cent of those eating two pots also did - but 55.1 per cent of those who stuck to their normal diet also reported an improvement. So you might as well rewrite the slogan: "55 per cent of people with digestive discomfort felt better after doing nothing."
 
The authors say this was a pilot study, and that the effect of advertising may have affected people's expectations of the product. “Further double-blind randomised controlled studies are required to confirm these health benefits”, they say. In other words you need to give one set of people the stuff, and as near a matching sample as you can manage something that looks and tastes like the stuff, and see if it makes any difference.
 
Activia claim that are committed to delivering the scientific evidence, and that 16 human clinical studies have been published. How surprising then that a study such as the researchers admit to be necessary is not available. Think how much more convincing the ad would be if it was supported by such scientific evidence– though of course if such a study showed that the probiotic did nothing, its commercial future would not be so healthy.