The manufacturers of probiotic yogurts and yogurt drinks have, in the past, claimed their products can help relieve digestive irregularity and boost the immune system. However, the European Food Safety Authority (EFSA), which regulates food health claims, has recently found insufficient evidence for claims that probiotic products have a positive effect on the immune system and digestive health. The food industry's probiotics sector, worth £200 million a year in the U.K., has complained that EFSA uses excessively rigorous scientific standards, similar to those used in the pharmaceutical industry, to assess claims.

However, expert professor Bob Rastall, head of Food and Nutritional Sciences at the University of Reading, firmly believes probiotics can be useful.

He stresses that probiotics are considered by some as "functional foods" -- products which have ingredients or components in them that can improve health or reduce disease risk in humans. "But they're not drugs; they don't prevent or cure disease," he warns.

The gut is full of bacteria, and in the colon there is a very complex "bacterial ecosystem" involving hundreds of species. Rastall says that some of the organisms in the gut are good for health: they stimulate the immune system and can inhibit pathogens (disease-producing agents), but others are less beneficial, causing toxins.

By increasing the population of the so-called good bacteria (probiotics), the health of the gut can be improved. According to Dr. Helen Crawley who works in Nutrition Policy at City University, most people who eat a good mixed diet, containing lots of vegetables, will have perfectly healthy functioning guts. However, there is some evidence that when people have been ill, or on antibiotics, they may benefit from foods which have probiotic properties.

"It's interesting to note that many foods have these," points out Crawley. "It's not limited to yogurts and yogurt drinks."

Probiotics have been shown in small studies to reduce the incidence of antibiotic-associated diarrhea in nursing homes, and the incidence and/or severity of irritable bowel syndrome (IBS), bloating, abdominal pain and flatulence in some people.

"The idea, really, is that probiotics are topping up the healthy bacteria in the gut," says Rastall.

He points out that several studies show the immune system is more responsive to pathogens after probiotic consumption.

"In a study on winter infections, people were fed probiotics and had the same incidence of infections like the common cold, but the duration was reduced by a couple of days. I would say that's a useful health benefit."

From the March 7, 2011, Prepared Foods E-dition