Yogurt is one of the few probiotic foods that Americans regularly eat. When we get enough probiotics -- friendly bacteria that help to drive out their bad counterparts and some yeasts -- we get a health benefit, according to a definition of the World Health Organization and the Food and Agriculture Organization of the United Nations cited by the U.S. Government's National Center for Complementary and Alternative Medicine.

But we get little probiotic benefit from some of the yogurt we eat....