THURSDAY, Aug. 16, 2012 (HealthDay News) -- So-called "yo-yo" dieting -- where people repeatedly lose weight by dieting, only to regain the weight -- may be frustrating, but it will not hurt a person's ability to lose weight over the long term, a new study finds.
This type of "weight cycling" does not have a negative effect on metabolism, the study found. The findings may be significant, the experts added, because yo-yo dieting affects up to 40 percent of the population in the Western world, and estimates indicate that nearly half of American women are currently dieting to lose weight.
"A history of unsuccessful weight loss should not dissuade an individual from future attempts to shed pounds or diminish the role of a healthy diet and regular physical activity in successful weight management," study senior author Dr. Anne McTiernan, a member of the Fred Hutchinson Cancer Research Center's Public Health Sciences Division, in Seattle, said in a center news release.
The researchers randomly divided 439 sedentary women in Seattle who were overweight or obese into four groups: a reduced-calorie diet only; exercise only (mainly brisk walking); reduced-calorie diet plus exercise; and a control group that didn't diet or exercise. The women involved in the study ranged in age from 50 to 75 years.
After one year, the investigators found that participants on the diet-only and diet-plus-exercise groups met their weight-loss goals and lost an average of 10 percent of their starting weight.
Overall, 18 percent of the women in these two groups were considered severe yo-yo dieters (they reported losing 20 or more pounds on three or more occasions), and 24 percent were moderate yo-yo dieters (they reported losing 10 or more pounds on three or more occasions).
Although severe yo-yo dieters were, on average, almost 20 pounds heavier than the women who were not yo-yo dieters when the study began, at the end of the study the researchers found no significant differences between those who had a history of yo-yo dieting and those who did not.
The weight cycling did not affect the women's ability to successfully participate in diet or exercise programs, the study authors reported. Yo-yo dieting also did not affect the percentage of body fat and lean muscle mass gained or lost among the women, they noted.
The researchers added that other factors -- such as blood pressure, insulin sensitivity and blood concentrations of hormones that help make people feel full or regulate blood sugar levels -- were also unaffected by yo-yo dieting, because they found no difference between the women who had these past fluctuations in their weight and those who didn't.
McTiernan's team cautioned that obesity is a known risk factor for many cancers, as well as heart disease and diabetes. This is particularly worrisome because two-thirds of the U.S. population is currently overweight or obese.
"We know there's an association between obesity, sedentary behavior and increased risk of certain cancers," McTiernan said in the news release. "The World Health Organization estimates that a quarter to a third of cancers could be prevented with maintenance of normal weight and keeping a physically active lifestyle."
The study was published online this week in the journal Metabolism.
The U.S. National Institutes of Health provides more information on weight loss and dieting.