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Yo-Yo Dieting Is Unlikely to Be Cancer Risk

17 agosto, 2015

Yo-Yo Dieting Is Unlikely to Be Cancer Risk

Nick Mulcahy

August 14, 2015The phenomenon of yo-yo dieting, or the intentional loss and then unintentional regain of 10 pounds or more, is not associated with overall cancer risk or specific risks for 12 cancers, according to investigators involved in the largest and most comprehensive study of its kind.
Yo-yo dieting, which is a popular term and is technically known as weight cycling, has been linked to cancer risk in a number of studies, but those have had notable limitations, according to the study investigators, led by Victoria Stevens, PhD, a researcher at the American Cancer Society (ACS) in Atlanta.
Their study was published online July 23 in the American Journal of Epidemiology.
The ACS investigators point out that nearly half of American adults are trying to lose weight, and most loss is regained. Therefore, if weight cycling was a cancer risk, it would be a broad public health issue.
The team addressed the issue on a grand scale by investigating «many more cancers than any previous study,» having the largest population, and including men, who have mostly been neglected in research to date, Dr Stevens told Medscape Medical News.
They analyzed the 42,498 men and 53,709 women enrolled in the Cancer Prevention Study II Nutrition Cohort, which was started in 1992.
Weight cycles were defined by default; the study’s baseline questionnaire asked the number of times at least 10 pounds was purposely lost but later regained.
The people who reported weight cycling were then categorized by the total number of cycles they reported: 1 to 4, 5 to 9, 10 to 19, and 20 or more.
In this 96,000-plus person analytical cohort, 25,317 first cancers occurred from 1994 to 2009.
When the investigators crunched the numbers, they found that weight cycling was not associated with overall risk for cancer in men (hazard ratio [HR] for at least 20 cycles vs no weight cycles, 0.96; 95% confidence interval [CI], 0.83 – 1.11) or women (HR, 0.96; 95% CI, 0.86 – 1.08).
The analysis was adjusted for body mass index (BMI), among other covariates. BMI might have confounded at least one study that found a link between breast cancer and weight cycling, according to Dr Stevens and colleagues, referring to a 10-year-old study (Am J Epidemiol. 2005;162:229-237).
Weight cycling was not associated with any of the 12 individual cancers investigated: prostate (both lower-risk and aggressive cases), colon, rectal, pancreatic, renal, esophageal, liver, non-Hodgkin’s lymphoma, multiple myeloma, lung, melanoma, and stomach.
«These results suggest that weight cycling, independent of body weight, is unlikely to influence subsequent cancer risk,» the investigators explain.
A notable limitation of this study is that there was no way to assess whether the «amplitude of gain/loss» was associated with cancer risk. In other words, are the men and women whose yo-yoing was more drastic — at least 25 pounds with each cycle — at risk for cancer?
«Unfortunately, there is no standardized definition of a weight cycle. Ten pounds may be low,» said Dr Stevens. As noted above, the weight-cycle amount was dictated by a questionnaire drafted in the 1990s.
But the 10-pound cycle is not an outlier in the body of weight-cycling research, she reported: «Some studies have used this amount, whereas others have used more.»
Among the study’s strengths is the fact that the questionnaire asked participants about «purposely» losing weight, according to the investigators. The element of intention is important because weight loss can occur with unhealthy behaviors, such as smoking, they point out. Some of the studies that have shown a link between weight cycling and cancer risk have failed to control for intentionality.
The American Cancer Society funds the Cancer Prevention Study II Nutrition Cohort. The authors have disclosed no relevant financial relationships.
Am J Epidemiol. Published online July 23, 2015. Abstract

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