Is Yogurt Good for You?

The pros and cons of probiotics.

What's so pro about probiotics?Good bacteria are having their moment—in yogurt, pizza, ice cream, even mattresses and aftershave. Dannon says that its probiotic yogurt Activia "helps regulate your digestive system," while its yogurt drink DanActive helps "strengthen your body's defenses." Jala asserts that its bacterially dosed ice cream fudge bars have "all the benefits of probiotics," again citing healthy digestion and an immune boost. Over at Naked Pizza, which boasts baked-in, heat-resistant bacteria, one of its co-founders blogs about how humans "came barefoot, naked and covered in bugs," even conjuring a woman squatting in childbirth until her newborn lands in some all-natural maternal feces. Then there are probiotic products purporting to fight bed bugs or alleviate the symptoms of autism.

No wonder the backlash is roiling. The Federal Trade Commission has gone after Dannon for overplaying the benefits of its probiotics. (The company reached a settlement though it did not concede any wrongdoing.) An army of lawyers has also attacked General Mills for advertising that its Yoplus-brand yogurt provides digestive health benefits. They argue that these claims lack scientific support and are "reasonably likely to mislead the public." The New York Times recently pilloried "foods with benefits," including probiotics, as well, questioning many of the rosy health claims made on their behalf. Even Stephen Colbert quipped last week about yogurt "supposedly full of good bacteria," saying, "Don't trust 'em. I always throw in a spoonful of Purell first."

But we shouldn't be too quick to throw the good bacteria out with the bad. Probiotics are, by definition, "live microorganisms which when administered in adequate amounts confer a health benefit on the host." But the diversity of these organisms—and the scope of their possible benefits—is much more extensive and complex than a quick stroll through the grocery store might suggest. Even different strains of a well-known genus like Lactobacillus can have different effects on the body, which makes careful research—and precise communication—critically important. Academic work suggests, for instance, that certain strains of probiotics may help to address a range of gastrointestinal ills, especially diarrhea. Alluring, if nascent, work also looks at different bugs' effects on the immune system, including their potential to fend off common infections or prevent allergic conditions in babies. Some papers speak to preventing sickness in healthy people. Others focus on treating disease. The problem isn't with any of this budding science. It's with marketing claims that exaggerate or are too vague to offer real guidance. (What does it even mean to "balance" digestion?) Beyond the fuzzy ad-speak of functional foods, it's time to pin down the real potential of these critters, attending to questions of safety and dosage and taking them seriously as medicine.

The literature on probiotics holds particular promise when it comes to the gut. Strong evidence suggests that several strains can help to treat or prevent diarrhea associated with viral infection or antibiotics. Less established, though fascinating, is the possibility that some may help relieve irritable bowel syndrome or treat disease linked to the superbug Clostridium difficile. The hope is that when our gut's ecosystem is thrown out of whack, specific probiotics might help rejigger the balance, allowing us to tend our own buggy gardens.

What about the immune system? Good bacteria may tweak the balance of immune cells or cause more cells to become activated, at least temporarily. In theory, this might help to fend off disease. Of course, "most people aren't as interested in, for example, how activated their macrophages might be as they are in keeping from getting sick," as Mary Ellen Sanders, a probiotics consultant who runs the company Dairy and Food Culture Technologies, puts it. The few studies that look at whether probiotics can help prevent common illness tend to find very modest benefits: A randomized trial of Finnish toddlers, for instance, suggested that those drinking a specific probiotic milk three times a day, five days a week, had about one sick day fewer over the course of seven months. It remains to be seen whether different strains (or combinations) might pack a bigger punch. At the same time, researchers are asking whether various bugs might help to prevent allergy if given early enough to breast-feeding mothers and babies, or whether they might reduce inflammation. None of this work is definitive, but it is intriguing early science.

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