BEIJING, April 23 (Xinhuanet) -- A recent study by researchers at the University of California, Los Angeles, reaffirmed what every overweight person hates to hear: losing weight is easy, keeping it off isn't.

    In other words, diets don't work.

    "If dieting worked, there would be a bunch of skinny people walking around," said obesity researcher Dr. David Katz, head of Yale University's Prevention Research Center, who did not participate in the latest study.

    Ask Roberta Perry. For more than 20 years she tried organized diet programs, prescription pills, psychotherapy, even hypnosis. And after years of yo-yo dieting, Perry realized it would take more than gimmicks to slim down.

    "As much as I would like to have a magic bullet, I knew the only way to lose weight was eat less and exercise more," said the 39-year-old public relations consultant.

    Her experience is a common one. The UCLA researchers analyzed 31 diet studies that followed people two to five years after they went on diets. Between one-third and two-thirds gained back the weight they lost. A small number were able to successfully maintain their weight loss.

    Since the 1970s, the ranks of overweight and obese Americans have risen with two-thirds of adults in that category. Obesity raises the risk of heart disease, diabetes and some cancers. Being overweight increases blood pressure and cholesterol levels which can lead to heart disease.

    Many factors can conspire against successful weight reduction, health experts say. Diets can be boring and there's always a temptation to return to old habits. Serial dieters may also become discouraged and give up when their weight plateaus. People who lose too much too soon don't learn to make the overall lifestyle changes -- eating healthier foods and exercising regularly -- that are necessary to keep their weight stable.

    "It's just plain difficult to modify your diet and turn away from the pleasures of eating," said Michael Goran, an obesity researcher at the University of Southern California. "We're driven to eat."

    The study appeared in the April issue of American Psychologist, a publication of the American Psychological Association.

    (Agencies)