"The general experience thus far is that the best effects are obtained with combinations of probiotics rather than single LAB [lactic-acid bacteria] treatments," says Professor Bengmark.

The most severe form of bowel disease is cancer-of either the colon or rectum. Again, probiotics may be of use here, too. Researchers have noticed an association between a high intake of yoghurt or probiotics and lower rates of colon cancer (J Nutr, 2000; 130: 384S- 90S). So far, trials have shown a significant protective effect of probiotics on colon cancer, and even a tiny curative effect-at least in rats, so it may not apply to humans (Carcinogenesis, 2002; 23: 1953-60).

Guts apart
The link between probiotics and gut conditions is fairly predictable. The real detective work has been to uncover the connections between probiotics and diseases unrelated to the gut.

One breakthrough has involved allergies, perhaps because they are immune-related. The 'hygiene hypothesis', for example, posits the idea that allergies are caused by overzealous cleanliness, particularly in childhood-but our immune system needs to be exposed to bacteria to begin working. So far, trials of probiotics involving allergic children and adolescents have generally been disappointing, but some researchers argue that's because they have been given too late in life to work.

Five years ago, Finnish doctors were the first to examine probiotics in early infancy. Having located more than 100 mothers-to-be with a family history of allergic eczema, they gave their newborns either probiotics or a placebo for the first six months of life. Follow-up of the babies at age two revealed that eczema was halved among those taking the probiotics (Lancet, 2001; 357: 1076-9).

Similar studies on other allergies have had less favorable results, with no particular benefits found in asthma or food allergies and intolerance. This is surprising as one of the major theories of food allergy is the 'leaky-gut' hypothesis (mentioned above).

Experts now believe that the answer lies in a huge research program that has been designed to test both individual strains as well as cocktails of lactobacilli. A few small-scale probiotic pharmaceutical companies have already begun testing their own semi-exclusive probiotic cocktails.

As for female urinary tract and vaginal infections, most studies have shown that single probiotics haven't prevented or cured them, although an Austrian company has found that three Lactobacillus strains (L. rhamnosus GR-1 and L. reuteri B-54 and RC-14) do work (World J Urol, 2006; 24: 28-32). And there's some tantalizing preliminary evidence of a place for probiotic cocktails in cirrhosis, pancreatitis and postoperative infections, too.

To date, this non-drug therapy is in its infancy. Only a fraction of the 500 gut-flora species has been explored so far, and few but the most advanced researchers understand that the specific strains of bacteria residing in our intestines may be related to maintaining health by keeping particular illnesses at bay. What's already clear is that we need to change how we view health and immunity to something that doesn't just start and end with our own bodies.

Tony Edwards - WDDTY vol 17 no 10 (2007)