Yo-yo dieting may weaken immune system

Donna Erie is a classic yo-yo dieter. In the last four years, she lost 60 pounds on a liquid diet, 35 pounds with a combination of herbal weight-loss pills and four hours of daily exercise and 15 pounds on the Atkins plan.

Each time, however, she put the weight back on.

"I've been dieting forever," says the 51-year-old secretary for the city of Los Angeles.

Carrying 210 pounds on her 5-foot, 7-inch frame, Erie's aware of studies showing that weight reduction decreases the risks of diabetes and other illnesses. She's determined to slim down to thwart the diabetes that both her parents developed.

But diet and nutrition experts are concerned about the potential health consequences for people such as Erie who repeatedly lose and regain pounds.

Nutrition educators at the University of California, Berkeley, recently reported that women who began dieting before age 14 were not only heavier but also were more than twice as likely to have dieted more than 20 times than women who began restricting their calories later. Lead author Joanne Ikeda said those who begin this pattern of losing and regaining pounds before puberty could disrupt their physical development.

Now, there's new evidence that yo-yo dieting may weaken the immune system.

Researchers at the Fred Hutchinson Cancer Research Center in Seattle measured the effectiveness of natural killer cells, which attack viruses and cancers, in a study of 114 obese, sedentary women ages 50 to 75. Each woman was asked how many times she had taken off at least 10 pounds in the previous two decades.

Among women who had lost weight at least five times, natural killer cell function dropped 30 percent, the researchers reported. The immune cells are part of the body's complex defense against illness and infection.

Scientists aren't sure how much disease-fighting power must be lost to create harm, said lead researcher Erin D. Shade, a nutritionist. However, she said, a crucial finding was that the immune-system effects persisted as many as 15 years after women had last dieted.

At a time when an estimated 50 percent of American women and 25 percent of American men are either dieting or thinking about dieting, such findings reinforce the wisdom of sticking with a sustainable weight. They underscore the need for more research into yo-yo dieting, which has become a lifestyle for many people.

"Weight cycling has been somewhat neglected by the research community," said Cornelia Ulrich, a research epidemiologist and senior author of the immune-system study.

Kelly D. Brownell, director of the Yale Center for Eating and Weight Disorders in New Haven, Conn., sees compelling reasons to determine whether the practice might leave some people worse off than carrying excess weight: "It has implications for the ethics of putting people on diets, especially the diets that haven't been tested."

Shade's report in the June Journal of the American Dietetic Association follows a 2001 report in the Journal of the American College of Cardiology that yo-yo dieters had 7 percent lower levels of high-density lipoprotein, the good cholesterol. The amount of lowering was "directly proportional to the amount of weight cycled" and was independent of physical activity, obesity or waist measurement, said study author Dr. C. Noel Bairey Merz, a cardiologist at Cedars-Sinai Medical Center in Los Angeles.

Such reports have grabbed the attention of Weight Watchers International, said Karen Miller-Kovach, the company's chief scientific officer. An ongoing study of 1,000 successful Weight Watchers followers who reached healthful weights includes questions designed to determine "how many have weight-cycled and if their past is predictive of their future," Miller-Kovach said.

She said previous studies haven't differentiated between regaining pounds in a matter of months or in a matter of years, which might also affect health. "As is so often the case, the devil is in the details," she said.

Although questions about the safety of repeated dieting remain unanswered, the basic recipe for better health stands: Eat better and exercise more.

Alison E. Field, an assistant professor of pediatrics at Harvard Medical School in Boston and author of studies that found weight gain, rather than yo-yo dieting, boosted the risks of hypertension and diabetes, says that weight loss shouldn't be discouraged but that the goal should be gradual and permanent change.