Half of all probiotic health drinks do not contain the healthy bacteria they claim on the label, a panel of microbiologists warned yesterday. Recognised brands made by Yakult, Danone, Müller or Nestlé do not dupe consumers. But up to 25 products - many of which are sold via the web - do not contain the right bacteria, or contain it in too small quantities.
Shoppers should be suspicious unless the probiotic drinks and capsules state they contain lactobacilli or bifidobacterium and stipulate a minimum of 10 million bacteria per bottle.
The warning was made by Glenn Gibson, professor of food microbiology at the University of Reading, together with Dr Sandra McFarlane, a microbiologist at Dundee University, and Professor Christine Edwards, head of human nutrition at Glasgow University.
So-called "healthy bacteria" account for 10-15% of the bacteria in the gut in adults, but become depleted through poor diets - such as too much fatty, low fibre, preservative-laden food - environmental factors, antibiotics and stress.
Probiotic products seek to redress the balance, and consumers are increasingly buying into the idea of replenishing their supplies of "healthy bacteria" with the UK market for probiotic yoghurt drinks and yoghurts being worth £307m in the year up to July.
Research published by the Food Standards Agency last year indicated that some probiotics do reach the gut but found that, out of 35 bacterial strains in 12 commercial products, only lactobacillus was sufficiently robust to survive the whole digestive process.
Yesterday, Prof Gibson, who led the research, warned that half of the 50 products available in the UK contained the "wrong" bacteria and were of no benefit.
"Half the products on sale don't contain the bacteria they say on the label. As a rule of thumb, you can trust the big manufacturers. Their quality control is very good. It would be disastrous for Nestlé, Danone or Yakult to have these other organisms in their products," he said.
"On the other hand, there are a lot of manufacturers - many of which sell products on the web - who are unheard of and these are the ones to worry about. Half of the products you can buy have got the wrong bacteria in them, the wrong amount, or are completely sterile.
"There's no legislation to protect you against this at present," he added.
He cited a powder called Acidophilus that contained an organism called clostridia, which makes spores that can be resistant to antibiotics.
Products that are safe include Activia, Immunitas, Digestivas, Yakult, Actimel, Vitality and the tablet Multibionta.
The scientists also advised that anyone over 65 should take the products. Past this age, the number of healthy bacteria decrease 1,000-fold to around just 2% of the gut's natural flora.
Anyone taking antibiotics should also take a probiotic, as should people going into hospital in the hope that it might help ward against hospital-acquired infections such as MRSA or clostridium difficile.
Prof Edwards said the ideal would be for people to look at their entire diet, but with only 8% of Britons eating a healthy diet, functional foods such as probiotics may be necessary.