A liquid diet like the one that shaved 67 pounds off talk-show host Oprah Winfrey should be attempted only by certain people, after conventional diets fail and under a physician's supervision, dietitians say.

After Winfrey discussed her four-month slimdown Tuesday on her show, about 5,000 telephone calls an hour began to pour into Sandoz Nutrition Corp., which sells the Optifast diet program she used, said company spokesman Jim Parsons.The Optifast program is offered to the public only by hospitals and physicians, Parsons said.

But liquid diet programs "were not made for the majority of dieters who want to lose 10 or 15 pounds," said Mary Lee Chin, a Denver consulting dietitian and spokesperson for the American Dietetic Association.

Such programs generally should be considered only by people who exceed their ideal weight by at least 20 percent or who face a medical risk because of their weight, Chin said. Liquid diets also should be tried only if conventional diets fail, she said Wednesday.

People also should avoid liquid diets if they are pregnant or have kidney or liver diseases, cancer or a recent heart attack, she said.

Chin also listed diabetics who requires insulin, but Karen Miller Kovach, assistant director of nutrition services at the Cleveland Clinic, said she considered diabetics potentially eligible after a thorough evaluation.

Chin and Kovach warned against buying liquid diet products at stores and using them without medical supervision.