Some Bacteria for Brunch?

Health-boosting probiotics are all the rage, but shop carefully.

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Corrected on 12/3/07: The patent on the probiotic bacteria known as LGG expired in June 2006. An earlier version of this article implied that LGG was still patented.

Corrected on 11/30/07: An earlier version of this story said that Kashi claims no particular health benefit from the strain of bacteria contained in its probiotic-enriched cereal and that the strain has been subjected to few published studies. It is more correct to specify "peer reviewed" studies, and the company does say the probiotic strain promotes an increase in friendly intestinal microbes.

Naked Juice Co. of Azusa, Calif., launched a new juice smoothie this fall that contains an unlikely ingredient—live bacteria. Certain cereals, baby formulas, dairy drinks, and other food products have also had such microbes intentionally added during their manufacture. These are just the latest in a glut of foods and beverages that contain probiotics, which are harmless microorganisms that have a variety of potential health benefits. At least some of these microbes appear capable of improving digestion, preventing diarrhea, or strengthening the immune system, studies show. However, many probiotic-containing products have not been subjected to rigorous research. So consumers must shop carefully in order to benefit.

Probiotics is a term for various "friendly" micro-organisms—certain types of bacteria and yeast—that may provide consumers with health benefits. It might seem counterintuitive to gobble bacteria for better health, but a healthy human gut teems with hundreds of varieties, most of them harmless or even beneficial. Those microbes, most commonly strains of Lactobacilli and Bifidobacteria, vastly outnumber the body's human cells and help maintain a healthy digestive system, in part by inhibiting the growth of potentially infection-causing microbes.

Taking probiotics may be most helpful when a person's normal collection of gut bacteria has been disturbed, which can result from food poisoning, for example, or from using antibiotics. Those drugs can kill helpful and harmful microbes alike. Some evidence suggests that popping a capsule full of probiotics or downing a teeming cup of yogurt each day might help prevent gastrointestinal infections in the first place—and may combat some chronic conditions such as irritable bowel syndrome and allergies. Food makers are also touting additives called prebiotics, a fancy term for fibers and sugars that can help probiotic bacteria thrive. Recent research suggests that prebiotics might hold many of the same benefits as probiotics.

No guarantee. Labels on supermarket shelves can be misleading, however. Products and pills that contain probiotics and prebiotics aren't necessarily proven to work. "All probiotics are not equal," says William Chey, a gastroenterologist at the University of Michigan. Even strains of bacteria that share the same Latin name may work differently, says Gary Huffnagle, professor of internal medicine at the University of Michigan and coauthor of The Probiotics Revolution. "Among Lactobacillus acidophilus," he says, "there are really potent [beneficial] strains and others that just make yogurt." That species and other lactobacilli help turn milk into yogurt, which is one reason that dairy products dominate the probiotic-food market. The bacteria must be added to most other products.

One of the most-tested probiotic strains is Lactobacillus rhamnosus GG, which is found in the dietary supplement Culturelle and Dannon's Danimals yogurt. Since 1985, when scientists at Tufts University discovered it, "LGG" has been subjected to hundreds of studies and found to be beneficial against diarrhea, dental infections, and respiratory infections. A study in the British Medical Journal last August found that the strain could also treat childhood diarrhea; in the trial, kids who consumed an LGG-packed supplement recovered in three days on average rather than five days.

But since LGG was patented until June 2006, some companies used other L. rhamnosus strains that have not been tested as rigorously. Other bugs appear to help in certain chronic ailments. The supplement called Align, for example, contains Bifidobacterium infantis 35624, which has been proposed as a possible remedy for irritable bowel syndrome. That disorder may affect as many as 1 in 5 Americans and is marked by bloating, abdominal pain, and irregular bowel movements. (The product also can lessen "a range of episodic digestive upsets," according to manufacturer Procter & Gamble.) A recent analysis of 13 clinical trials involving various probiotics showed that the bacterium in Align was the only one to have been proved efficacious for IBS.