NEW YORK (AP) _ Talk-show host Oprah Winfrey's weight loss of 67 pounds has spurred new interest in liquid diets, but experts said Wednesday many people should avoid such diets and nobody should try them without medical supervision.

''These were not made for the majority of dieters who want to lose 10 or 15 pounds,'' said Mary Lee Chin, a Denver consulting dietician and spokesperson for the American Dietetic Association.

Winfrey, 34, announced on her show Tuesday that she had lost the weight in four months through a supervised liquid diet program, and that a cheeseburger was the only solid food she had eaten since July 7.

Chin said liquid diet programs should be considered only by people who are above their weight by 20 percent to 30 percent, or by at least 50 pounds, or whose weight poses a medical risk. And a liquid diet should be considered only after conventional diets fail, she said.

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

She also listed diabetes that 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 recommended against simply buying liquid diet products at stores and using them without medical supervision.

For one thing, liquid diets provide essentially a starvation diet of 800 calories a day or less, and that can cause medical harm unless the symptoms are spotted early, Chin said. For example, such a diet can cause muscle wasting as well as mineral imbalances that can lead to heart malfunctioning, she said.

Medical supervision also helps in dealing with side effects of the diets, which can include dizziness, constipation, dry skin, hair loss and intolerance of cold temperatures, Chin said.

In addition, Kovach said, people who follow a liquid diet without supervision may not realize they have such conditions as kidney disease that means they should avoid such diets.

And people who do the diets on their own tend to regain the weight they lost once they return to solid food, Kovach said. They miss a key component of supervised liquid diet programs, a maintenance program to teach the person to keep the weight off, she said.

Maintenance programs stress the importance of exercise and changing the behaviors that led to the excess weight, Chin said. Winfrey, on her show, pointed out that ''the fact that she lost the weight doesn't mean she can keep it off without exercise,'' Chin said.

Apart from looking for medical supervision and a maintenance program that will allow significant individual attention, Chin and Kovach offered these tips for choosing a liquid diet program:

- Make sure the diet provides high quality protein, which includes the eight essential amino acids, and that it fulfills the recommended dietary allowances for vitamins, minerals and protein. The protein will be high quality if it is from an animal source, Chin said.

- Besides a physician, the program should include a nutritionist, an exercise physiologist and a behavioral counselor to help in keeping weight off.

- Ask about long-term success rates. One program says that after 2.5 years, 18 percent to 41 percent of dieters keep off the weight they lost, which is a ''significant success rate,'' Chin said. If the program offers no statistics, she said, ''I'd look at another program.''

- Look for an incentive to keep dieters in the program, such as prizes or other reward systems for weight loss.