About two-thirds of Americans are overweight or obese, and many are trying to shed the extra pounds. Over the long term, however, most people who lose weight through dieting regain it later.

The health effects of such weight cycling, also called yo-yo dieting, are a matter of controversy.

Several studies have found that people whose weight cycles up and down tend to die earlier. But the majority of that research failed to differentiate between intentional weight loss and weight loss due to disease such as cancer, researchers write in the new report.

In the current work, nearly 56,000 men and more than 66,000 women answered questions about how often they had intentionally lost 10 or more pounds and later regained the weight. The participants were between 50 and 74 years old when the study started in 1992.

During a 16-year follow-up period that ended in 2008, roughly 15,000 men and 10,000 women died.

A total of 42 percent of men and nearly 57 percent of women in the study reported intentionally losing and then regaining at least 10 pounds one or more times in their life.

Among women whose weight yo-yoed the most -- 20 times or more -- 16 percent died over the study, compared to 15 percent of those who said their weight never cycled due to dieting.

For men, the corresponding numbers were 29 percent and 26 percent.

But as it turned out, participants whose weight cycled the most were also more likely to be heavy 10 years prior to the start of the study, which could raise their risk of death.

When the researchers accounted for that, as well as health problems such as diabetes, high blood pressure and smoking, the gaps in death rates disappeared.

"Our study shows that the act of weight cycling itself does not increase your risk of premature death," Victoria Stevens of the American Cancer Society in Atlanta told Reuters Health.

Her findings are published in the American Journal of Epidemiology.

Still, experts don't recommend yo-yo dieting, but rather slow-paced, sustained weight loss.

"While weight cycling may not kill you any sooner, yo-yo dieting is still not good for a whole lot of other reasons," Judy Caplan, a dietician in private practice in Virginia, told Reuters Health.

"Yo-yo dieters are great at losing weight, but not at maintaining the weight loss, which can leave a person demoralized," said Caplan, who is also a spokesperson for the Academy of Nutrition and Dietetics and was not involved in the new research.

Previous research has suggested that yo-yo dieting can slow metabolism and may actually contribute to more weight gain in the long run.

But for those who find their weight yo-yoing after dieting, the new findings contain a hopeful message.

"I think the study is encouraging," said Simone French, a behavioral scientist who specializes in obesity prevention at the University of Minnesota and was not involved in the work.

"It shows that people shouldn't be afraid to keep trying to lose weight, because they think it will increase their health risks if they gain it back."

SOURCE: bit.ly/yEhPg3 American Journal of Epidemiology, online January 27, 2012

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