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`Yo-yo Dieting' May Weaken Immunity, Study Says

Posted - Jun. 4, 2004 at 6:23 a.m.



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The Seattle Times

(KRT)

SEATTLE - Doctors have long said that repeatedly losing and regaining weight won't sculpt the body of your dreams. Now, Seattle researchers have found that so-called "yo-yo dieting" might even make you sick.

A recent study by the Fred Hutchinson Cancer Research Center and the University of Washington says frequently losing and regaining weight may weaken the immune system, leaving the dieter more susceptible to illness.

In a study of overweight but otherwise healthy women, scientists found that people who intentionally lost and regained weight five times or more in the past 20 years had a weakened immune system compared to those who maintained the same weight for five or more years.

The results provide strong evidence that yo-yo dieting could be a health risk, said Cornelia Ulrich, senior author of the study and an assistant member of Fred Hutchinson's Public Health Sciences Division.

This new information could serve as a warning to the 50 percent of women in Western countries who the study says are trying, or have recently tried, to lose weight.

"To our knowledge, this is the first study to show potential long-term effects of yo-yo dieting on health," Ulrich said. Previous studies, she said, have focused on the short-term effects fasting and weight loss can have on the immune system.

A weakened immune system can lead to increased susceptibility to colds and infections, and perhaps even cancer, she said.

The current study, which was funded by the National Cancer Institute, was published in the June issue of the Journal of the American Dietetic Association.

Ulrich and her colleagues interviewed 114 sedentary, postmenopausal women from the Seattle area about their weight-loss history for the past 20 years. The women, whose ages ranged from 50 to 75, had maintained a stable weight for at least three months before participating in the study.

Scientists used natural-killer-cell activity to measure immune-system function. Natural killer cells, or NK cells, are a vital part of the immune system, important for fighting viral infections and even cancer, Ulrich said.

The researchers collected the cells from blood samples drawn from each participant. Then, scientists measured NK cell activity based on the cells' ability to kill leukemia cells. NK cell activity was about 30 percent lower in women who had intentionally lost at least 10 pounds five or more times in the past 20 years.

One weight-loss episode of 10 pounds or more during the past 20 years was not associated with significantly different immune-system function, Ulrich said, but NK cell activity decreased as the number of weight-loss episodes increased.

Although the results are intriguing, Ulrich said, the research is preliminary and has limitations. The researchers, for example, relied on self-reported weight-loss histories, not medical records. The results would also be stronger, she said, if the blood samples had been taken several times over a long period of time instead of just once.

"Following people over time would give us a stronger understanding of how weight cycling impacts long-term immune function," she said, adding that she and her colleagues hope to conduct a long-term study in the next two years or collaborate with similar research being done in Canada.

The findings are not meant to suggest that those who are battling the bulge should give up.

"There is indisputable data showing that if you are overweight or obese, you improve your health if you lose weight," Ulrich said. "What we're concerned about is that people often regain weight."

Exercise is one way dieters can keep weight off, she said. It also can boost the immune system and blunt the negative effects weight loss could have on immune function, she added.

Yo-yo dieting could also make it harder for you to lose weight, said Lola O'Rourke, a spokeswoman for the American Dietetic Association.

"The psychological effect of repeated failure and success can have a deleterious effect on the motivation to lose weight," she said, adding that weight fluctuation also can slow metabolism.

Instead of trying the latest fad diet, O'Rourke suggests, you should make small changes in food choices that you can live with for a lifetime.

Cindy Farricker, a registered dietitian who works with the University of Washington and has a private practice in Bellevue, Wash., echoed that advice and also recommended figuring out exactly what makes you over-eat.

"These diets don't get to the heart of this issue," she said, adding that many people eat not because they're hungry but as a response to certain emotions.

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Keeping the weight off

-Eat only when hungry.

-When eating at home, take smaller portions than usual; go back for more only if you're still hungry.

-When eating out, ask for a to-go box at the beginning of your meal and put away half of your food before you start eating.

-Don't eat from a large bag of chips when snacking. Take out the amount you'll eat and put the bag away.

-Don't eat in front of the television. Studies show you'll eat more and eat more junk food.

-Include at least one nonstarchy fruit or vegetable serving in every meal and snack.

-Choose whole-grain bread over white bread.

-Avoid soft drinks and sugary juice drinks.

-Skip the blended, sweetened coffee drinks and go for a latte with nonfat or low-fat milk.

-Get plenty of sleep. Studies show sleep loss can promote fat storage.

Source: Erin Shade, University of Washington Medical Center clinical nutritionist

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(c) 2004, The Seattle Times. Distributed by Knight Ridder/Tribune News Service.

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