But as often happens with new health products, probiotics have been overmarketed and oversold. The claims are seductive: Pills, powders, and solutions containing "friendly" bacteria will boost the immune system, prevent cancer, and perform other health "miracles."
This sort of over-the-top hype is typical of many "natural" supplements. But that doesn’t mean it is based on total fiction. All the usual limitations apply: The studies are small, the results inconsistent, the findings often limited to animal experiments. Nonetheless, the evidence suggests that probiotic therapy could be useful someday as a form of preventive medicine – and not just for diseases of the gut.
Actually, probiotic therapy is an old idea. Almost a century ago, Elie Metchnikoff, director of the Pasteur Institute, argued that Bulgarian peasants live long lives because they ate yogurt containing Lactobacillus bacteria. In the 1930s, Minoru Shirota, a Japanese physician, maintained that the right mix of gut bacteria could prevent disease. But working out the practical details of these theories hasn’t been easy. The lingering questions include: Which bacteria should be used and who will benefit and under what circumstances?
The gut has considerable help in striking this balance between barrier and conduit: Some 500 different kinds of bacteria inhabit a healthy intestine. Collectively, they’re known as the gut microflora. These "good bacteria" compete with and tend to crowd out disease-causing bacteria by keeping them from attaching to the intestinal wall and by secreting agents that the invaders find toxic. The native bacteria also provide protection by stimulating the patches of lymphoid tissue embedded in the wall of the intestine, causing them to churn out antibodies against invading pathogens.
Just as a pollutant can ruin a lake or a river, invading viruses or bacteria can wreak havoc to this finely balanced ecosystem. If the pathogens win the battle, the gut wall becomes too permeable. The intestine becomes inflamed. A similar disruptive effect is sometimes observed when oral antibiotics wipe out some of the healthful microflora along with the bacteria that are causing the illness.
The basic notion behind probiotics is pretty straightforward: Restore the depleted ecology of the intestine with new, healthful bacteria. The bacteria most commonly used as probiotics fall under the general heading of lactic acid bacteria. These bacteria feed on sugars and produce lactic acid, which is part of the reason they are so useful in the food industry: By generating acid and lowering the amount of sugar, they make foods like yogurt, cheese, and sauerkraut inhospitable environments for disease-causing organisms. Some yeasts, principally Saccharomyces boulardi, have also been used as probiotics.
The bacterial strains tested most often belong to the Lactobacillus and Bifidobacterium genera. So far, researchers have had more success with a strain called Lactobacillus GG than with any other. "GG" is for the initials of the Tufts University researchers who isolated it, Sherwood Gorbach and Barry Golding. Researchers and manufacturers are competing to show that their particular strain works best. Some companies are also marketing probiotics that contain a combination of as much as eight different kinds of bacteria.
Stefano Guandalini, a University of Chicago pediatric gastroenterologist, has published results from a multicenter study in Europe that found value in probiotic therapy for children with diarrhea, regardless of cause. He reported in the January 2000 issue of the Journal of Pediatric Gastroenterology and Nutrition that when children hospitalized with severe diarrhea were treated with an oral hydration solution containing Lactobacillus GG, they had a shorter course and a shorter hospital stay than children given the oral solution alone.
When people take antibiotics that alter the gut’s microflora, a bacterium called Clostridium difficile often seizes the opportunity, propagates, and produces a toxin. In severe cases, this leads to colitis, an acute inflammation of the lining of the intestine. Two years ago, two large and credible studies, one American and the other Finnish, showed that probiotic therapy reduced the diarrhea experienced by children taking antibiotics for respiratory tract infections. But in other studies on antibiotics, the results have been negative. So the value of probiotic therapy for gut problems caused by antibiotics remains controversial.
The evidence for travelers diarrhea also ping-pongs. British soldiers traveling to Belize and Finnish tourists visiting Turkey weren’t protected by the probiotics they took, according to studies published several years ago. However, when a different probiotic was tested on American tourists travelling to these same areas, the diarrhea was cut in half.
• Bowel diseases. Two years ago, Irish investigators reported results from a small, randomized trial that showed Lactobacillus GG reduced the number of unformed bowel movements in patients with irritable bowel syndrome who have diarrhea. But for pain, urgency, and bloating, the probiotics weren’t any more helpful than the placebo used in the trial. You can find reports in the published medical literature that probiotic therapy might help people with Crohn’s disease but they’re preliminary.
• Allergies. A study published in the April 7, 2001 issue of the Lancet hinted that probiotics might be used to prevent allergies. Expectant mothers in the treatment part of the study took two capsules of Lactobacillus GG daily for two to four weeks before delivery, which was followed by a six-month course for the infant. Infants who received the bacteria had a rate of chronic allergic eczema half that of infants who didn’t.
• Immunity. Various studies have hinted that probiotics might boost the effectiveness of vaccines. Other researchers have shown that they might promote overall health by revving up the immune system. For example, a study published in the June 21, 2001 issue of the British Medical Journal found that children attending daycare centers in Helsinki who drank milk spiked with Lactobacillus GG had 17 percent fewer respiratory infections and had them 11 percent less often during the seven-month study than children drinking regular milk.
Though we still don’t have solid proof of the efficacy of probiotic therapy today, it does seem like a promising treatment modality, for at least some medical conditions, in the future.