Bowl of bran cereal
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You can't turn on the TV these days without seeing an ad touting the benefits of yogurt, cereal, even ice cream, "now with added fiber." But does a bowl of high-fiber Rocky Road really deliver the same benefit as a bowl of bran?

Hardly. Like dietary fiber (the roughage found in whole foods), fiber additives pass undigested through the gastrointestinal tract, so the FDA accepts them as the real deal. Yet no scientific studies link these artificial fibers to the health benefits—including a lowered risk of heart disease and obesity—associated with naturally fiber-rich foods. "The additives are enjoying fiber's halo without having proven themselves," says Bonnie Liebman, director of nutrition at the Washington, D.C.–based Center for Science in the Public Interest.

Added fiber also doesn't have the ability to turn junk food into a nutritional superstar, says Amy Jamieson-Petonic, a spokesperson for the American Dietetic Association. She says it's best to get your fiber from fruits, vegetables, and whole grains, since they deliver nutritional value that goes far beyond keeping you regular. One high-fiber carrot, for example, contains some 500 beneficial compounds, says Jamieson-Petonic. "You're not going to get that from additives."

Next: Are fiber supplements safe? Dr. Katz sorts out the healthy, the harmful, and the hype