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Yo-yo dieting is famously unhealthy, if only for the havoc it wreaks on your mood and self-esteem. Now there’s another reason to opt for the kind of slow, gradual weight loss you’ll be able to maintain: A new study has found that yo-yo dieting can interfere with your immune system.
Researchers at the Fred Hutchinson Cancer Research Center in Seattle recruited 114 healthy postmenopausal women who were overweight or obese (with a body mass index between 25 and 40) to assess their weight loss histories and the cell-killing power of their natural killer (NK) cells. These immune cells knock out cancer cells and cells infected with viruses; when their potency diminishes, risk of cancer and infection can rise.
The more times a woman had intentionally lost weight, the lower the killing power of her NK cells. The women who had stayed within the same weight range for the longest period of time had the best NK cell profiles.
The results shouldn’t be used as an excuse not to shed pounds; the idea is to maintain a healthy weight over time. Exercise is key, say the authors: Previous studies have shown that it both helps maintain weight loss over time and boosts immune function.
It may help you lose weight, but the Atkins and other low-carb diets may not be so great for your health, some experts say. Another voice joining the chorus of naysayers is the Physicians’ Committee for Responsible Medicine (PCRM), which recently issued an advisory decrying the health risks of these high-protein/low-carb plans. “The long-term is our main concern,” says Neal Barnard, president of the PCRM, “and there are many reasons to think this isn’t a healthy way to eat for life. First, there is massive calcium loss with this diet, even in the maintenance phase, which you can be on forever. Second, daily meat eaters have been shown to have a 300 percent higher risk of colon cancer. And third, the diet is high in saturated fat and low in fiber, both of which contribute to heart disease.” The PCRM advisory also links long-term use of high-protein diets with osteoporosis, renal disease, and diabetes.There’s some evidence, though, that meat-heavy diets might not harm the heart. Published research on the Atkins diet, which was introduced in 1972 by physician Robert Atkins (who declined to be interviewed for this article), has been notoriously scarce. But in a study last summer at Duke University, subjects who stayed on the diet for six months actually saw their heart profiles improve. Their total cholesterol stayed the same, but their HDL numbers went up and their triglyceride levels dropped. Barnard is unmoved by these findings. “Many of the subjects in the Duke study also exercised and took supplements,” he says. “So you can’t conclude the improvements were caused by the diet alone.” Actually, Eric West-man, the associate professor of medicine who led the study, presented equally positive heart-related results from another Atkins diet study to the American Heart Association last fall—and this time he did factor the volunteers’ eating and supplement habits into the final data. Yet even he isn’t ready to give the Atkins diet a ringing endorsement. “Based on current research, we can’t say it’s 100 percent safe,” he allows. “We need more time and more study.” Many experts seem to agree that the diet is probably benign if you don’t stay on it too long. What no one can answer —for now at least—is how long is too long?