Postmenopausal（绝经后的） women who gained weight during adulthood¹ had an increased risk for endometrial（子宫内膜的） cancer compared with women who maintained a stable weight, according to data from the American Cancer Society's Cancer Prevention Study II Nutrition Cohort. Victoria L. Stevens, Ph.D., strategic director of laboratory services at the National Home Office of the American Cancer Society in Atlanta, presented the data at the 10th AACR International Conference on Frontiers in Cancer Prevention Research, held Oct. 22-25, 2011.

Stevens and colleagues investigated whether adulthood weight gain and/or weight cycling, defined as the number of times a woman purposefully lost 10 pounds or more and then later regained² the weight, increased the risk for endometrial cancer in postmenopausal women, independent of body mass index (BMI). Weight cycling, commonly referred to as "yo-yo" dieting, had previously³ been suggested to increase the amount of fat mass relative to lean body mass, according to Stevens.

"Fat tissue is the major source of circulating estrogen（雌性激素） in postmenopausal women, and estrogen promotes the development of endometrial cancer," Stevens said. "Therefore, we hypothesized that weight cycling could be associated with risk for this cancer because women who engage in this behavior may have a higher proportion of fat than noncyclers."

The researchers collected data from 38,152 women with an intact（完整的） uterus and who provided information on weight history and weight cycling on a 1992 questionnaire. Between 1992 and 2007, 560 women reported a diagnosis⁴ of endometrial cancer.

Overall, the results indicated that there was an almost fourfold increased risk for endometrial cancer in women who had gained 61 pounds or more in that timeframe, compared with women who maintained a stable weight. After adjustment for baseline BMI, the researchers found a twofold increased risk for endometrial cancer.

In addition, after adjustment, the researchers found no association between weight cycling, or yo-yo dieting, and endometrial cancer risk. "Weight gain during adulthood may increase risk for endometrial cancer in postmenopausal women, but weight cycling, which results from unsuccessful attempts to lose weight, does not increase risk for this cancer," Stevens said.

Future research should address whether the timing⁵ of weight gain and weight cycling during specific parts of adulthood, such as early adulthood versus⁶ middle age, influences the risk for endometrial cancer and whether weight loss decreases this risk, Stevens said.

"Weight gain during adulthood should be avoided to minimize risk for endometrial cancer," she said. "Women who have gained weight and are overweight or obese⁷ should continue to attempt to lose weight even though most weight loss will not be maintained."