A history of unsuccessful weight loss should not discourage future attempts to lose weight, according to a new study on women out of the Fred Hutchinson Cancer Research Center.

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Diet news is never just plain good.Good would be something like “Eating chocolate causes you to lose weight and gain lean muscle mass, study finds.”

The latest, out of Fred Hutchinson Cancer Research Center, is not like that.

Yo-yo dieting, researchers have found, actually doesn’t change your metabolism and make it harder to lose weight in future efforts, as widely believed. So just because you’ve lost and gained, lost and gained, lost and gained, you now have no excuses. Do it again. And likely, again.

Dr. Anne McTiernan, of The Hutch’s public health-sciences division, the senior author of the study published online by the journal Metabolism, sees the results as a half-full kind of thing.

“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,” McTiernan said.

The study was designed for a slow, steady and reasonable amount of weight loss — 10 percent of body weight within six months and maintenance for the next six — with daily calories of 1,200 to 2,000, calculated by each woman’s beginning body weight.

Earlier studies have suggested that repetitive weight loss-regain cycles may increase a dieter’s preference for dietary fat, perhaps because of changes in metabolic rate, immune function and body composition, the authors noted. But few studies have actually examined this notion, which suggests that somehow dieting causes a person’s body to become more efficient at holding onto fat, they said.

For the study, McTiernan and her colleagues enrolled 439 overweight to obese, sedentary Seattle-area postmenopausal women, ages 50 to 75.

Obesity, the researchers said, is a known risk factor for many cancers, as well as for heart disease and diabetes, and with two-thirds of the U.S. population overweight or obese, it’s a worry for those in public health.

And for the nearly half of American women estimated to be currently dieting, any help understanding what’s going on with their recalcitrant fat may be very welcome.

The women in the study were randomly assigned to one of four groups: One got a diet that reduced calories by 500 a day. Another, a brisk-walking assignment with no diet. The third group was told to diet and exercise, and the last group got no intervention.

At the end of the yearlong study, those in the diet only and diet-plus-exercise groups lost an average of 10 percent of their starting weight, which was the goal of the intervention.

The exercise-only group lost an average of 2.4 percent of starting weight.

Overall, weight loss among the women who had a history of severe or moderate weight cycling didn’t differ significantly from those who had not repeatedly gained and lost pounds.

In addition, there wasn’t much difference in the percentage of body fat or lean muscle mass gained or lost, their blood concentration of hormones, insulin sensitivity or blood pressure.

Of the 439 women, 18 percent had a history of severe weight cycling (having deliberately lost 20 or more pounds on three or more occasions) and 24 percent had a history of moderate weight cycling (losing 10 or more pounds on three or more occasions).

“To our knowledge, no previous studies have examined the effect of prior weight cycling on the body composition, metabolic and hormonal changes induced by a comprehensive lifestyle intervention” of such women, the authors wrote.

Because the study was only a year, it wasn’t able to capture longer-term effects, the authors said. It also wasn’t able to measure the degree to which larger or more frequent weight-loss episodes may influence metabolism or hormones.

McTiernan said they did follow some of the women for a longer period of time and are analyzing those results now.

Doctors also have been frustrated by their patients’ unsuccessful attempts to lose weight, the authors said, but some have been reluctant to recommend weight loss to otherwise healthy patients for fear that weight-loss cycling could make them less healthy.

This study shows that a history of unsuccessful weight loss should not discourage future attempts, the authors said. But it’s important to use healthy and sustainable weight management, they added, as recent work showed weight regain is more likely when people use unhealthy weight control strategies.

And regain may have undesirable consequences. When a person loses weight, a portion of the weight loss is fat and a portion is muscle, said Caitlin Mason, a postdoctoral fellow at The Hutch and a study co-author. “Some evidence suggests that after weight regain, the muscle mass is not fully recovered,” she said. “Thus, there could be a small net gain in fat mass.”

The study, which was funded by the National Institutes of Health, the National Cancer Institute and the Canadian Institutes of Health Research, also included investigators at Harvard Medical School, the National Cancer Institute, and the University of Washington.

Carol M. Ostrom: 206-464-2249 or costrom@seattletimes.com.