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People who undergo bariatric surgery for weight loss may have a lower risk of cancer and death, a new study suggests. VICTOR TORRES/Stocksy
  • Researchers investigated the effects of bariatric surgery for weight loss on cancer risk and mortality.
  • They found that bariatric surgery reduced cancer risk by 25% and mortality by 43%, especially in women.
  • However, further studies are needed to understand underlying mechanisms.

Around 21% of deaths in the United States in 2019 were linked to cancer. Thirteen types of cancer are linked to obesity, including two of the most common types of cancer: colorectal and breast cancer.

Currently, 42.5% of adults in the U.S. are classed as having obesity, and 31.1% are overweight. Meanwhile, severe obesity is known to increase the risk of death from cancer by 62% among women and 52% among men.

While studies show that higher body mass index (BMI) is linked to increased cancer risk, it is less clear whether ways to reduce BMI reduce cancer risk.

Studies show that bariatric surgery—various surgical procedures that change the digestive system to facilitate weight loss—is linked to clinically significant weight loss and that it modulates cancer-relevant biological mechanisms that may reduce incidence and improve mortality for some cancers.

Understanding more about the effects of bariatric surgery on cancer rates and outcomes could inform preventive strategies for cancer.

Recently, researchers analyzed long-term healthcare data from patients who had bariatric surgery. They found that the surgery was linked to lower cancer incidence and cancer mortality.

The study was published in the journal Obesity.

For the study, the researchers analyzed healthcare data from 21,837 patients who had undergone bariatric surgery between 1982 and 2018 alongside data from 21,837 controls who had not undergone surgery who were matched for age, sex, and BMI.

Procedures included:

  • Gastric bypass: reducing the size of the stomach and directing food to the middle part of the small intestine
  • Gastric banding: when a silicon band is placed around the stomach to reduce stomach capacity
  • Sleeve gastrectomy: when part of the stomach is separated and removed from the body
  • Duodenal switch: a combination of a sleeve gastrectomy and a gastric bypass

The patients were followed for between 2.8 and 13.5 years, and around 79% of patients were female. Both groups had an average BMI of around 46 at the beginning of the study. A BMI of 30 or more is considered in the obesity range.

Ultimately, the researchers found that patients who had bariatric surgery were 25% less likely to develop any cancer compared to the nonsurgical comparison group. They were also 43% less likely to die from cancer than those who did not undergo surgery.

Men vs. women

Women who underwent surgery were 41% less likely to develop obesity-related cancers, such as breast, ovarian, uterine, and colon cancer. Additionally, they had a 47% reduced mortality for any kind of cancer compared to women who did not undergo surgery. This included a 55% reduced mortality for obesity-related cancers and a 38% reduced mortality for non-obesity-related cancers.

Meanwhile, bariatric surgery was not linked to reduced overall cancer mortality or obesity-related cancer mortality in male patients. It was, however, linked to 51% lower cancer mortality with non-obesity-related cancers.

The researchers wrote that the sex-specific findings are consistent with previous research.

The researchers also noted that cancer mortality was significantly lower after gastric bypass surgery than after gastric banding or sleeve gastrectomy. They noted that the sample size for a duodenal switch was small and that it was thus not possible to compare it to gastric bypass surgery.

Medical News Today spoke with Dr. Ted Adams, Ph.D., adjunct professor of internal medicine at the University of Utah, corresponding author of the study. He said that a hormonal mechanism may be at play as bariatric surgery had a particularly strong effect on obesity-related cancers among women.

He added that ongoing research is focusing on other possible reasons that might explain why increased cancer risk occurs with obesity. These include chronic inflammation, increased release of steroid hormones, and promotion of tumor growth stimulated by high blood glucose from insulin resistance.

“It follows that perhaps patients who have had weight loss surgery may have reversed the cancer-causing factors cited in the previous sentence and thereby lower cancer risk,” he said.

MNT also spoke with Dr. Joshua Cohen, the medical director of the gynecologic cancer program at City of Hope Orange County and a board certified gynecologic oncologist, who was not involved in the study, about how bariatric surgery may affect hormone levels and thus lead to weight loss.

“Excess body fat produces estrogen, a hormone which cancers like uterine cancer, ovarian cancer, and estrogen receptor-positive breast cancer may depend on to grow. So, like links in a chain, weight loss from bariatric surgery may help reduce estrogen levels, which in turn may decrease an individual’s risk of certain gynecologic cancers, estrogen receptor-positive breast cancer, as well as overall cancer risk.”
— Dr. Joshua Cohen

MNT spoke with Dr. Abraham Krikhely, a bariatric and general surgeon at Columbia University Irving Medical Center, not involved in the study, about its limitations.

He noted that while the study demonstrates a correlation, it does not establish a cause-and-effect relationship.

He added that most patients had a gastric bypass, meaning that it is less clear how other bariatric operations affect cancer risk.

Dr. Adams further noted that the results for men may be skewed as only 21% of participants were men and that the study lacked longitudinal BMI measurements, nutritional and physical activity assessments, and data on smoking history, which may have also affected the results.

Dr. David Voellinger, a bariatric surgeon at Novant Health in Charlotte, North Carolina, who was not involved in the study, told MNT that the study highlighted the effects of weight loss in treating cancer.

“Bariatric surgery can be used to not only decrease the incidence of certain cancers but also decrease the mortality associated with them. Also, primary care physicians and oncologists should look more closely at weight loss and bariatric surgery as tools for treating cancer,” he said.

This study adds to the large body of literature that there are major benefits to bariatric surgery in [people with obesity] provided stringent selection criteria are used. Future studies are needed to see if similar long-term benefits occur in patients who undergo medical treatment with some of the newer drugs such as Ozempic and Mounjaro.”

Dr. Anton Bilchik, Ph.D., surgical oncologist, chief of medicine, and director of the Gastrointestinal and Hepatobiliary Program at Saint John’s Cancer Institute at Providence Saint John’s Health Center in Santa Monica, California, who was not involved in the study, speaking to MNT.

“The study’s implications are that there are many long-term benefits of weight loss surgery; when people think of obesity, increased cancer risk is not the first thing that usually comes to mind,” Dr. Mir Ali, bariatric surgeon and medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center in Fountain Valley, CA, who was not involved in the study, told MNT.

“This study may help people who meet the criteria for surgery but are still hesitant to take that step see the additional scope of benefits,” he added.

Things to consider before surgery

Dr. Cohen suggested, however, that women considering treatments that affect hormone production, such as birth control pills or bariatric surgery, should first speak with a healthcare professional about potential health risks.

“While bariatric surgery may be an effective treatment for severe obesity, it is also an intermediate– to high-risk surgery,” he said.

He added that the best way to ‘stop cancer’ is to prevent it in the first place—by adopting a healthy diet and an exercise routine.

“Working with your medical provider and a nutrition counselor is very important to help you meet your goals and incorporate positive changes that fit your lifestyle to help reduce your risk of developing cancer,” he concluded.