Do probiotics really do anything?

This woman may be getting a healthy dose of bacteria AND catching up on e-mail. See more staying healthy pictures.
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The United States is known for its multitasking at mealtime. While other cultures enjoy long, leisurely meals, Americans head to the lunch meeting, in which a sandwich is accompanied by statistics. At dinner, we find ourselves juggling cell phones, children and the evening news while we eat. It's no wonder then that Americans find themselves interested in improving their health while they eat their favorite foods. Maybe we buy the juice claiming to have extra vitamins or the snack bar boasting of its full-day supply of fiber. That's some mighty multitasking -- eat some food you were going to eat anyway and get a health benefit. And market research has found that people would rather eat food with something healthy than take another pill, which is why functional foods, or food with an added health benefit, have become big business.

Take Activia, a yogurt made by Dannon. In the first year that Activia was on the market, it racked up more than $100 million in sales in the United States [source: Martin]. Activia is probably the most well-known example of a product fortified with probiotics, and Activia's success portends a lot of interest in loading probiotics into other functional foods. Europe and Japan have been hip to probiotics for awhile now. But what are probiotics, and why should we care about a yogurt packed with them?

While a lot of American shoppers may have been attracted to Activia by celebrity spokeswoman Jamie Lee Curtis, they actually have the people of Bulgaria to thank for their probiotic yogurt. At the beginning of the 20th century, Russian scientist Elie Metchnikoff determined that a diet of fermented milk products resulted in a long, healthy life for Bulgarian peasants [source: Sanders]. Probiotics, meaning "for life" in Greek, became the term for the bacteria that was found in those fermented products. The bacteria have a very technical definition provided by the World Health Organization; they are "live microorganisms which, when administered in adequate amounts, confer a health benefit on the host" [source: Brody].

But what this means in practice can frankly be as confusing as Bulgarian to an English speaker. In essence, proponents of a probiotic diet say that probiotics are "good" bacteria that are needed in the gut, and that their presence could result in a whole host of health benefits, everything from reducing lactose intolerance to curing yeast infections. Critics of the probiotic movement, however, say that the evidence just isn't there for these claims, and that what's more, even if the science did demonstrate the benefits, it would be impossible to fill the right amount of these bacteria into a food product. So who's right? Should you add probiotic products to your shopping list, or do they do nothing at all?