Yo-yo dieting, in which you repeatedly lose weight and then put it back on again, can damage your immune system for a long time—like a yo-yo that doesn't come back up, according to a new study reported in the Journal of the American Dietetic Association. Lower immune function can leave you vulnerable to disease.
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Many people in America yo-yo as they try a diet for a few months, drop a few pounds, then drop the diet and pile the pounds back on. Then they try a different diet and go through the cycle again. Diets are just hard to stick to, and these weight fluctuations are often the result.
The effect on your immune system may last longer than the effect on your waistline, say researchers at the Fred Hutchinson Cancer Research Center in Seattle. They measured the levels of immune cells called natural killer cells—they go after foreign invaders like bacteria and viruses—in a group of middle-aged women. The 114 women, who had all passed through menopause, were all overweight but otherwise healthy, and over the previous 20 years some had repeated yo-yo episodes, losing 10 pounds or more and then gaining weight back. Those who did this five or more times had natural killer-cell activity levels that were one-third lower than those of women who went through only one yo-yo cycle.
Weight loss is good, says Cornelia Ulrich, one of the researchers, but she's concerned that this pattern of weight loss (and gain) can be bad. This is the first study to show that yo-yo dieting might have long-term health effects, she says. The research does have limits: Ulrich and her colleagues asked the women to recall their dieting history long after the fact, so their memories might not have been accurate. A study that starts with a group of women and then follows them closely for several years to compare the effects of yo-yoing would carry more weight, scientifically. But still, this is an important clue that the common phenomenon of off-again, on-again weight loss is a strain on the body and that dieters need to add features to their weight-loss plans—regular exercise or dieting with a buddy—that help people stick with them.
