When you think about obesity, you may not connect it to cancer. However, researchers long have suspected a link between certain cancers and weight. Among those are endometrial, ovarian, colon, liver, pancreatic and postmenopausal breast cancers, which together contribute to 15 to 20% of all cancer deaths in the U.S.

Cancer risk increases with obesity

More than one-third of adults in the U.S. are considered obese with a body mass index (BMI) of 30 or higher. BMI is the measure of body fat of body fat based on weight and height. The number of people with severe obesity, which is a BMI of 40 or higher, has increased significantly. According to one study in the New England Journal of Medicine, if a person's BMI goes up by even five points, their cancer risk increases by 10%.

Those who are obese are two times more likely to develop cancer than those of optimal weight. For example, the risk for endometrial cancer increases sevenfold with a BMI of more than 40.

The greater risk of cancer appears to be due to excess body weight in the form of fat. Obesity causes fat cells in the body to increase. As the number of these fat cells goes up, the body's release of hormones changes. These changes tend to increase pro-inflammatory hormones and estrogen. This chronic inflammatory state can lead to damage in cells and the DNA in them, increasing the risk of certain types of cancers.

Researchers are studying the role body fat plays in chronic inflammation. In addition, hormones like estrogen and insulin resistance can lead to chronic metabolic diseases, including diabetes. By 2050, the Centers for Disease Control estimates that 1 in 3 adults will have diabetes along with its associated health complications.

Bariatric surgery and reduction of cancer risk link

Researchers believe a decrease in inflammatory fat cells could reduce cancer risks, but more research is needed. And it's still unknown to what extent cancer risk is reversed with nonsurgical, also called intentional, weight loss.

But for anyone who has lost weight with lifestyle changes, the challenge is keeping it off. The body has many complex neurohormonal systems in place to avoid starvation, making it difficult to maintain weight loss.

At this time, bariatric or metabolic surgery is the most effective treatment for obesity available, even when compared with medications and intensive lifestyle therapy. After surgery, people typically lose 50 to 70% of their excess weight or 25 to 35% of their total body weight, which often is sustained for many years.

Continuing research

Several large studies have been conducted to explore the link between weight loss through bariatric surgery and the reduction of cancer risk.

In a 2019 article in the Annals of Surgery, more than 22,000 people who had bariatric surgery were compared with 66,000 who didn't. The study participants were matched by sex, age, study site, BMI and other factors. Statistical models were used to look at the incidence of cancer up to 10 years after bariatric surgery compared to nonsurgical participants.

Those who had undergone bariatric surgery had a 33% lower risk of developing any type of cancer during the follow-up period compared to those who didn't have bariatric surgery. The results were even stronger when the outcome was restricted to obesity-associated cancers.

A 2022 study in the Journal of the American Medical Association followed 30,000 people, all with a BMI greater than 35. The participants were divided into two groups and matched by factors including age and sex. One group of about 5,000 patients had undergone bariatric surgery; the other group of just over 25,000 patients didn't have surgery. The median follow-up period was about six years.

The follow-up showed that bariatric surgery was associated with a significant reduction in the risk of obesity-related and other cancers. It also showed that patients who had undergone bariatric surgery had a decrease in cancer-related deaths compared with those who didn't have the surgery.

Researchers continue to delve into why and how bariatric surgery is reducing the risk of cancer and diabetes, and more studies are needed to confirm these results. However, there is promise for patients struggling with obesity that bariatric surgery can decrease metabolic diseases like diabetes and possibly the risk of cancer.

If you're considering bariatric surgery, this new evidence about its effectiveness and benefits may help you decide. It's another topic to discuss with your primary care provider or bariatric surgery team.

Maria Linnaus, M.D., is a bariatric surgeon in Eau Claire, Wisconsin.

This article originally published on the Mayo Clinic Health System blog.

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