The incidence of obesity continues to rise dramatically and the diseases which can occur due to obesity are becoming increasingly prevalent. Excessive weight increases the likelihood of high blood pressure, high cholesterol, diabetes, stroke, coronary disease, and kidney disease. It also increases the likelihood of certain cancers, such as colon, prostate, breast and uterine. In fact, 14 percent of cancer deaths in American men and 20 percent in women may be due to overweight or obesity. Therefore, if obesity contributes to death and disease, it would stand to reason that weight-loss would cut the risk, and research increasingly bears out this assumption.


The latest evidence comes from a Swedish study that shows obese women who had bariatric surgery had a 42 percent reduction in cancer risk, compared with conventional obesity management. However, the exact reason why the surgery had a beneficial effect remains unclear, as the researchers could find no direct link with either weight loss or a reduction in food intake. “The current exploratory report on cancer further underlines the favorable effects of bariatric surgery, particularly in women,” the authors concluded. “The intriguing but unproven possibility that the beneficial effects of bariatric surgery on cancer are mediated by mechanisms other than weight loss or reduced energy intake needs to be further explored.”

The Swedish Obesity Subjects (SOS) study, led by Dr. Lars Sjostrom of the University of Gothenburg, included 4,047 participants (71 percent women); 2,010 obese patients who had bariatric surgery and 2,037 matched obese control patients, all with an average BMI of 40. Over the 10-year follow-up, the bariatric surgery patients lost an average of 44 pounds, whereas those in the control group gained about 3 pounds. The surgery group also had an overall cancer risk reduction of 33 percent, primarily due to the significantly lower rate among women, where there were 79 first-time cancers in the surgery group, and 130 in the control group.

However, cancer incidence was virtually identical among men in both groups, with 38 cases in the surgery group and 39 in the control group. Dr. Andrew G. Renehan, of the University of Manchester, England, whose commentary accompanied the study, said “the absence of effect in men might simply reflect small sample numbers. For women, the greatest cancer-prevention effects from weight reduction are likely to be for postmenopausal breast and endometrial cancers, two hormone-sensitive malignancies, the effects of which might manifest within a decade,” noting that the effects of weight reversal might take much longer to become apparent for obesity-related cancers, such as colon, rectal, and kidney, which are more common in men.

But Dr. Leena Khaitan, a bariatric surgeon at University Hospitals Case Medical Center in Cleveland, said the lack of benefit in men is likely due to who has the surgery. “We know 80 percent of patients who undergo weight-loss surgery tend to be women. I suspect if we had larger numbers of men, we would probably see a difference.” She said this study and others like it suggested weight-loss surgery could be an important way to prevent costly, chronic diseases like cancer. “It’s a strong argument for preventive medicine.”

Three previous studies also showed significant reductions in cancer risk following bariatric surgery. “Taken together the studies provide the strongest evidence yet that weight reduction in obese individuals in association with subsequent reduction in cancer incidence strengthen the cause for causality between adiposity and cancer,” Dr. Renehan said. He added that “as the obesity epidemic shows few signs of abating, the incidences of obesity-related cancers may rise. However, the establishment that the development of these cancers is reversible brings about an encouraging new paradigm in cancer prevention.”

The study and accompanying commentary was published in the journal Lancet Oncology.