In a study published in JAMA, researchers provide the strongest evidence yet supporting the link between obesity and cancer, and the benefits of weight-loss surgery in lowering the risk of developing or dying from cancer.
The trial involved more than 30,000 patients with obesity: some of whom had bariatric surgery for weight loss, and some who served as non-surgical controls and received standard care for their obesity, including information about diet and exercise. Results showed that 10 years after surgery, people had a 32% lower risk of developing 15 common cancers, and a 48% decreased risk of dying from cancer, compared to those who had not had the weight-loss operation.
“What we’ve observed here is a very large effect,” says Dr. Steven Nissen, a cardiologist at Cleveland Clinic and the senior author of the paper. “I think this data is as strong as is going to be available for quite some time to support yet another reason why weight loss is a really important public-health intervention.”
Dr. Ali Aminian, director of the bariatric and metabolic institute at Cleveland Clinic and the study’s first author, says that in order for people with obesity to lower their risk of developing or dying from cancer, they need lose a considerable amount of weight—more than most people can sustainably drop with diet and exercise alone. The people in the study received one of two types of bariatric surgery between 2004 and 2017: 66% in the surgery group received gastric bypass, in which the surgeon divides the stomach into two smaller pouches and reroutes a part of the intestine to both sections, and 34% received gastric sleeve surgery, a procedure in which the surgeon removes 80% of the stomach, leaving a sliver the size of a banana. (Aminian says that since then, gastric sleeve procedures have become more common in the U.S., accounting for 65% to 70% of bariatric surgeries.) These procedures can help people to lose 20% to 25% of their body weight, which the researchers say is the threshold for seeing benefits when it comes to cancer risk. (While Aminian and several of the other study authors have received grants from Medtronic, which makes devices for bariatric surgery, the company was not involved in the JAMA study.)
“I want more primary care physicians to have serious conversations with their patients about the consequences of obesity and the reversibility of the morbidity and mortality associated with obesity,” says Nissen. “The primary care physician can start the conversation with their patients to consider surgery and determine if they are eligible.”
Obesity can influence cancer risk in a number of ways. Studies have shown that fat cells aren’t inert, but very metabolically active. They make substances that contribute to inflammation in the liver, which “creates a toxic environment that can increase the risk of cancer,” says Aminian. Obesity can also contribute to increases in hormones like estrogen, which have been linked to higher risks of breast and uterine cancer in women. In fact, the study found that endometrial cancer was among the diseases most closely associated with obesity, and that bariatric surgery reduced risk of endometrial cancer by 53%—more than any other type of cancer analyzed in the study.
While the study found that surgery, and the dramatic weight loss associated with it, were linked to a significant reduction in cancer, both Nissen and Aminian acknowledge that with nearly 42% of people in the U.S. now qualifying as obese, surgery is not a practical option for all of them. Not all will qualify for the invasive surgery, which comes with significant risks as it involves major rerouting of the digestive tract. Diet and exercise alone generally do not result in weight loss as significant as the type seen in the study, primarily because it’s challenging for people to adhere to the strict regimens required for continued weight loss.
Several weight-loss medications have recently been approved by the U.S. Food and Drug Administration that could lead to significant enough weight loss, similar to that achieve from surgery, but they aren’t being widely used yet as a tool to combat obesity. Nissen is currently leading a study of 15,000 patients sponsored by Eli Lilly, which makes one of the drugs, tirzepatide, that is approved for treating obesity in people with Type 2 diabetes and has helped them to lose up to 25% of their body weight. Results from that study might provide more confidence for primary care doctors to help their patients optimize weight-loss strategies and help prevent health risks including cancer.
“One tool is in the hands of surgeons, and now there are tools in the hands of non-surgeons [in the form of drug treatments,]” says Nissen. “Between these two strategies, I actually think there may be light at the end of the tunnel.”
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