Probiotic drinks work - but who knows how or why?

New research from Imperial College London and the Nestlé Research Center, Lausanne, Switzerland, says that probiotic drinks and yoghurts help the gut but it is unclear how or why.

Such products are usually marketed with claims that they can enhance digestion and health in general by boosting the number of "friendly" bacteria in the gut.

This has led to a huge commercial success with millions buying such products on a regular basis.

However some in the scientific community doubt their value saying that probiotic drinks and yoghurts contain too few bacteria to have any impact.

The latest research however does appear to suggest that they have a clear effect on the body, by changing the make-up of bacteria in the gut and the way the body processes fat.

Researcher Professor Jeremy Nicholson says their study show that probiotics can change the dynamics of the whole population of microbes in the gut and have an effect.

However he says they are still trying to understand what the changes might mean in terms of overall health.

For the study, researchers gave two different types of probiotic drink to mice that had been transplanted with human gut microbes.

The researchers compared the levels of different metabolites in the liver, blood, urine and feces of mice who had received treatment with probiotics and those that had not and found that treatment with probiotics had a whole range of biochemical effects and changed the makeup of the bugs in the gut.

The study showed that different strains of probiotic bacteria affect the body in different ways and the research team say this insight raises the prospect of developing probiotic products tailored to the needs of different groups of customers.

Co-researcher, Dr. Sunil Kochar, who works for Nestle, says that understanding changes triggered by so-called beneficial bacteria is an important prerequisite in efforts to develop customised nutritional solutions to maintain and/or enhance health and wellness.

Dr. Kochar says the results of the study are highly promising.

Earlier research has suggested that probiotics help prevent bowel conditions such as ulcerative colitis, protect children against allergies and may even reduce the risk of colon cancer and may also be useful for older people, bolstering levels of "friendly" bacteria which dwindle with age.

Probiotic drinks and foods may also benefit those on antibiotics by replacing the "good bacteria" killed off by the drugs.

Critics however remain dubious and say other studies have cast doubt on the worth of probiotic products.

Experts too say many on the market do not work as they contain either the wrong bacteria or the wrong amounts.

The best-known brands, including Yakult, Actimel and Multibionta, apparently do work properly, but consumers should be aware that most contain large amounts of sugar.

The study is published in the journal Molecular Systems Biology.