Dieting Can Weaken Immune System

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Study:

Dieting Can Weaken Immune System

June 2, 2004

SEATTLE (AP) -- A new study has found that

" yo-yo dieting " -- repeatedly losing, then regaining weight -- may

harm a woman's immune system. The study by the Fred Hutchinson Cancer Research Center also found that maintaining the same weight over time

appears to have a positive effect on a woman's immune system, according to

one of the lead researchers.

Researchers in the study, published Tuesday

in the Journal of the American Dietetic Association, interviewed 114

overweight but otherwise healthy sedentary, older women about their

weight-loss history during the past 20 years. The women had to have

maintained a stable weight for at least three months before joining the

study, which was funded by the National Cancer Institute.

The study, which found that long-term immune

function decreases in proportion to how many times a woman has intentionally

lost weight, measured natural killer cell activity in the women's blood.

Natural killer cells are an essential part of the immune system, killing

viruses and leukemia cells, said Cornelia Ulrich, senior author and an

assistant member of the Hutchinson Center's Public Health Sciences Division.

Low natural killer cell activity has been

associated with increased cancer rates and a higher susceptibility to colds

and infections, she said.

" While one weight-loss episode of 10

pounds or more in the previous 20 years was not associated with current

natural killer cell activity, more frequent weight-loss episodes " were

associated with a significant decrease in such activity, Ulrich said.

The study found that women who maintained a

fairly stable weight over several years had higher levels of such cells than

those whose weight frequently fluctuated.

Those who reported losing weight more than

five times had about a third lower natural killer cell function, the study

found. Conversely, women who maintained the same weight for at least five

years had 40 percent greater natural killer cell activity as compared to

those who maintained their weight for fewer than two years.

Though no men participated in the study and

further research is needed, Ulrich said the immune systems of male dieters

would likely be affected the same way.

The findings, while intriguing, are

preliminary, cautioned Ulrich, who is also a research assistant professor in

epidemiology at the University of Washington School of Public Health and

Community Medicine.

Researchers had to rely on the participants'

own reports of their weight loss histories and the analysis was based on

blood samples collected at a single point in time, representing a narrow

sample.

A long-term study could provide more

conclusive results, said Ulrich, who is planning to collaborate with Canadian

researchers who have been working on a similar study.

Although the study suggests that yo-yo

dieting is harmful, Ulrich stopped short of saying that people should stop attempting

to lose weight.

" There's clearly evidence that weight

loss is beneficial for your health, " she said. " What we're

concerned about is this pattern of weight cycling where women go up and

down. "

Exercise has been shown to boost immunity

and temper some of the negative effects of weight loss on the immune system,

Ulrich said.

Despite its preliminary nature, the study is

significant, said Tallmadge, a spokeswoman for the American

Dietetic Association in Washington,

D.C. Although dietitians have known for years the negative

psychological effects of yo-yo dieting, this appears to be the first study to

examine the long-term impact of such dieting on immunity, she said.

People should avoid popular low-carb and low-fat diets that can produce initial weight

loss but rarely work in the long term, Tallmadge said.

" Study after study shows that more

moderate restrictions are more likely to last permanently, " Tallmadge said. " That's why we registered dietitians are

urging people not to do the fad diets, and just try small changes that

they're more likely to be able to live with -- even if the weight loss is

slower. "

Copyright 2004 The

Associated Press. All rights reserved. This material may not be published,

broadcast, rewritten, or redistributed.

Hugs,

Deanna