A group of leading food microbiologists yesterday called for wider use of probiotics, particularly among elderly people, as well as tighter rules on labelling, so that specific details are provided about the bacteria in products.

They said that about half of the probiotics available were inaccurately labelled and did not do what they claimed, while some were found to contain unhealthy pathogens. Most of the serious offenders were sold over the internet and from unorthodox health food shops. The warning did not apply to mainstream brands used by the majority of people, such as those made by Danone, Yakult and Nestlé and sold as supermarkets own brands.

“Friendly” bacteria aid digestion in the gut and reduce the chances of stomach upsets. Research suggests that they also help to prevent bowel conditions and protect children against allergies, and may reduce the risk of colon cancer. Recently there has been an explosion in the use of probiotics, including yoghurt-style drinks, supplements and powders.

The group of scientists, led by Glen Gibson, Professor of Food Microbiology at the University of Reading, said that people should be aware of the benefits of maintaining balanced gut flora, including high levels of good bacteria. The most common types are species belonging to the lactobacillus and bifidobacillus families.

Experts believe that high-fat, low-fibre Western diets may contribute to a lack of friendly bacteria and an increase in harmful bacteria.

About 90 per cent of the bacteria in the gut of a newborn infant are friendly microbes, but this is reduced to 10-15 per cent in the average adult. After the age of 60 to 65, levels of friendly bacteria plummet 1,000-fold. “The elderly are definitely an excellent market for probiotic intake,” Professor Gibson said. “Awareness in the UK is increasing slowly but it is not great. It is a tricky concept to get over to people.”

He said it was no accident that in the world’s worst recorded case of food poisoning by the stomach bug E. coli 0157, all those who died were elderly. A total of 21 people were killed in Lanarkshire, Scotland, in 1996.

The research group said that one of the biggest obstacles in the way of useful probiotics was price, with a week’s supply sometimes costing about £3.

Probiotic products need to contain at least ten million bacteria to be effective. It is also vital that the bacteria survive their passage through the gastro-intestinal system. A recent study indicated that nine patients with ulcerative colitis, a form of inflammatory bowel disease that causes bloody bowel movements and abdominal pain, had 30-fold reduced levels of Bifidobacteria.

Four weeks after being given a Bifidobacteria probiotic, plus a sugary supplement to promote growth of the bacteria, they reported fewer symptoms. Many less well-known products did not live up to the promises made on their labels, the scientists said. They may not contain the numbers of bacteria advertised, and the microbes may not survive in the gut long enough.

Consumers were also advised not to trust brands of healthy yoghurt promoted as being probiotic without any specific information about the bacteria they contain. “There are a lot of products out there that no one has ever heard of, and this is where the problems arise. There’s no legislation,” Professor Gibson said. “You could buy a yoghurt-maker from Tesco, make your own probiotics, and sell them.” There were moves under way within the European Parliament to introduce controls on probiotics but the “wheels turn very slowly”.

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