For the study, researchers compared the risk of cancer diagnosis and death for more than 30,000 people with obesity, including more than 5,000 individuals who had bariatric surgery. Surgery was associated with a 32 percent lower risk of cancer and a 48 percent decreased chance of cancer-related death. “Patients can lose 20 to 40 percent of their body weight after surgery, and weight loss can be sustained over decades,” said the lead study author, Ali Aminian, MD, the director of the Bariatric & Metabolic Institute at the Cleveland Clinic in Ohio, in a statement. “The striking findings of this study indicate that the greater the weight loss, the lower the risk of cancer,” Dr. Aminian said. About two in five American adults have obesity, according to the Centers for Disease Control and Prevention (CDC). And obesity increases the risk of 13 types of cancer that together account for 40 percent of all tumors diagnosed each year in the United States, according to the CDC. In the study, those who underwent bariatric surgery lost an average of 25.5 kilograms (kg) (61 pounds [lb]) after 10 years of follow-up, compared with 2.7 kg (6 lb) without these operations. Surgery was associated with a significantly lower risk of obesity-related cancers, including malignancies of the breast, ovaries, uterine lining, colon, liver, pancreas, and thyroid. Overall, 2.9 percent of people who had weight loss surgery developed these tumors, compared with 4.9 percent of those who didn’t have operations. Bariatric surgery was also tied to a significantly lower risk of diagnosis and death from all cancers, including tumors unrelated to obesity, the researchers reported June 3 in JAMA. After a decade, 0.8 percent of patients who had surgery died of cancer, compared with 1.4 percent in the nonsurgical group. One limitation of the study is that the majority of the participants were female and white, so it’s possible the results might be different for men and individuals of other racial and ethnic groups. The study also wasn’t a controlled experiment designed to prove whether or how weight loss surgery might directly reduce cancer risk. It’s possible that excess weight accelerates tumor growth because it causes inflammation, impairs the body’s ability to use the hormone insulin to turn sugars from food into energy, and increases the production of sex hormones that play a role in the growth of some cancers, the study team writes. But it’s also possible that people who underwent surgery were healthier in other ways that helped prevent cancer, the researchers noted. They might have had healthier diets, exercised more, or been less likely to smoke than people who didn’t have bariatric procedures, for example.
