A Dietitian's View

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. There is a clinical study, right--

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. Also, Acidophilus and Bifidobacteria are less sensitive to stomach acid and more likely to make it into the colon alive than other names you might see on the label, such as Lactobacillus bulgaricus and Streptococcus thermophilis.

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.