Previous studies have suggested a link between obesity and increased cancer risk, and a new one bolsters that link by showing that weight loss seems to reduce cancer risk.
The researchers at McGill University in Montreal studied nearly 6,800 very obese people and found that weight loss surgery, including gastric bypass and gastric banding, can cut the risk of some cancer by as much as 80 percent. The strongest evidence was for breast and colon cancer risk reduction, but there was also a trend toward reduction in other cancers.
The research team, led by Dr. Nicholas Christou, director of bariatric surgery and professor of surgery at McGill, looked at the medical records of 1,035 patients who had the surgery and 5,746 who did not but were otherwise similar. None of the patients, who were in their mid- to late- 40s, had been diagnosed with cancer before the study.
During a five-year follow-up period, 2 percent of the surgery group was diagnosed with cancer, compared with 8.5 percent of the nonsurgery group. Christou, whose prior studies on weight loss surgery have shown a reduction in the risk of overall mortality, cardiovascular disease, and diabetes as well as cancer, said in a telephone interview that the most likely mechanism for the reduced risk of breast cancer is hormonal.
Fat tissue produces estrogen, which drives some breast cancers. In the latest study, the incidence of breast cancer was reduced by 85 percent in the surgery group.
“This effect is so strong it surprised a lot of people,” Christou said.
The risk of colon cancer was reduced by 70 percent in the surgery group, perhaps, Christou said, because after surgery, people eat less and ingest fewer carcinogens. It’s the weight loss per se, not the surgery, that packs the punch, he added.
“The point is to get the weight loss and keep it off permanently,” he said. The study was presented at a scientific meeting in June and will be published soon.
Dr. George Blackburn, a nutritionist at Beth Israel Deaconess Medical Center and associate director of the division of nutrition at Harvard Medical School, welcomed the study as further proof of the link between obesity and cancer.
Research shows that an estimated 10 percent to 40 percent of cancer cases in the United States are attributed to obesity, he said. The strongest links are between obesity and esophageal, kidney, endometrial, colon and some breast cancers, he said. But obesity also contributes to pancreatic, ovarian, and gallbladder cancers.
So, if you’re a candidate for weight loss surgery – if your body mass index is 40, or if it’s 35 and you also have another major disease – ask your doctor about the surgery, including how much it might lower your cancer risk.