Probiotics, the so-called friendly bacteria with health benefits, have broken out of the dairy case and are colonizing other areas of the supermarket.
But as manufacturers add the microbes to everything from infant formula and fruit juice to pizza, muffins and granola bars, experts caution that the word "probiotic" is widely misused by the industry and misunderstood by consumers.
While there are thousands of bacterial strains, only a few dozen have been tested for health benefits. Studies suggest some products may offer relief for digestive issues, but it's not known whether healthy people benefit from snacking on live "bugs."
There is no standard definition of probiotics, according to the Food and Drug Administration, but scientists generally say the term refers to foods, beverages or supplements containing live microorganisms that studies show promote health when people take enough of them. Without studies, products shouldn't be called probiotic, scientists say.
Scientists cannot yet explain exactly how probiotics work, but it's thought they can help restore beneficial bacteria in the intestinal tract.
"Some [bacteria] can produce enzymes that help digest food, while others can synthesize vitamin K in the gut or even help stimulate the immune system," Joe Schwarcz wrote in "An Apple a Day: The Myths, Misconceptions and Truths About the Food We Eat."
The bacteria may produce antibodies for certain viruses, produce substances that prevent infection or prevent harmful bacteria from attaching to the gut wall and growing there, according to the American Gastroenterological Association. But if those bacteria are wiped out by disease or medication, potentially harmful microbes may flourish.
For the consumer, finding the right probiotic can be vexing. Labels can't legally declare that the probiotic can cure, treat or prevent disease. So health claims, which don't require FDA approval, are often vague.
For example, Kashi's Vive is called a "probiotic digestive wellness cereal," one that "may restore your digestive balance."
And it may -- each serving contains a whopping 12 grams of fiber. But the probiotic used -- Lactobacillus acidophilus La14 -- has not been tested in humans eating Kashi Vive. And there's no guarantee that the microbes in the dry cereal are alive.
To make things more complicated, probiotics interact with bacteria already in the body, and everyone has slightly different microflora, said probiotic expert Gary Huffnagle, a professor of internal medicine and microbiology at the University of Michigan Medical School. So a product that works for one person might not be right for another.
Still, Huffnagle says one of the best things about probiotics is they're safe and your own trials should yield answers in a few weeks.
Bonnie Thompson, 43, of Ft. Collins, Colo., who suffered from irritable bowel syndrome for decades, tried several brands before finding one that worked: the Garden of Life supplement called Primal Defense.
Ultimately, the most effective probiotic was her own homemade kefir. "I credit it with normalizing my bowel function," she said.
NAVIGATING THE LABEL
Just because a food product says "probiotic" doesn't mean it's a probiotic. Even more aggravating, manufacturers often leave important information off the label, such as whether the product contains live organisms or the full name of the bacterial strain. Some advice:
-- Watch the dates: The organisms can die off while the product is sitting on the shelf. The best way to ensure it has an effective number of live bacteria is to look at the "best by" or expiration date.
-- Get enough microbes. Easier said than done. There is no single dosage for probiotics; studies have documented health benefits for products ranging from 50 million to more than 1 trillion colony-forming units (the measure of live microbes) per day. The amount you need is the amount that the study on your product showed was effective.
-- Scour yogurt labels. Look for yogurt products with "live and active cultures" and avoid the ones that say "made with active cultures." Those may have been heat-treated after fermentation, which kills the bacteria.
-- Scour yogurt labels, Part II. Remember that even "live, active cultures" aren't necessarily probiotics, meaning they may not have been tested for health benefits.
--Speak the lingo. A probiotic is defined by its genus (e.g. Lactobacillus), species (e.g. rhamnosus) and strain (a series of letters or numbers). "Products that list the genus and species and also the strain tend to have inherently better quality control and products," said probiotics expert Gary Huffnagle.
-- Watch for too-perfect names. Dannon calls its bacterial strains Bifidus Regularis (in Activia) and L. casei Defensis (in DanActive) -- for marketing purposes. These are made-up, consumer-friendly, trademarked names.