However, most regular yogurts either don't contain the right strains of bacteria, or contain levels that are so low they have no real effect on human digestive physiology, Sanders said.
Activia is somewhat different, she said, because the company has tailored the yogurt around a specific strain of bacterium with known digestive potency and greatly boosted the amount available in each serving. "They've also documented that the strain does survive intestinal transit, meaning that it has effects all the way through your intestine," Sanders said.
However, she agreed with Vasconcellos that spending about a third more per serving on Activia compared to a regular brand of yogurt might not make sense for everyone.
"Remember, if people just ate more fiber in their diets, more fruits and vegetables, they'd probably have bowel movements more frequently, anyway," Sanders pointed out.
And she noted that bowel-movement frequency varies widely between individuals, naturally. "It's not a real disease, and if it's not bothering you, what difference does it make?"
The Activia line has been a success for Danone, however, and more probiotic foods are following in its wake, including "Vive probiotic digestive wellness cereal," from granola-cereal maker Kashi. Sanders even noted that, "a small company just introduced chocolate candy bars with probiotics."
Other functional foods are getting airplay, too. Major beverage companies are hyping their new "fitness drinks," tapping into Americans' thirst for quick, easy nutrition. Brands like Gatorade's "Propel" come with dissolved antioxidants, such as vitamins C, E and some B variants.
"They tend to have more of these types of ingredients, but less carbohydrates than usual sports drinks," said Vasconcellos. "However, if you're taking in a balanced diet -- eating a wide variety of foods, plenty of fruits and vegetables, low-fat dairy, whole grains -- and drinking enough fluids, then these types of specialty drinks really aren't necessary," she said.
There's more on healthy nutrition at the American Dietetic Association.
SOURCES: Patricia Vasconcellos, R.D., CDE, dietitian and spokeswoman, American Dietetic Association, Boston; Mary Ellen Sanders, Ph.D., food microbiologist and consultant, president, Dairy and Food Culture Technologies, Centennial, Colo.