The Intersection Between Obesity and Cancer: How Weight Loss Affects Cancer Risk

| October 1, 2019 | 0 Comments

by Christopher D. Still, DO, FACN, FACP

Co-Clinical Editor of Bariatric Times; Medical Director for the Center for Nutrition and Weight Management, and Director for Geisinger Obesity Research Institute at Geisinger Medical Center in Danville, Pennsylvania.

Dear Colleagues:

As you all are aware, October is Breast Cancer Awareness Month, so I thought now is a good time to discuss obesity’s effect on breast and other cancers, most importantly emphasizing weight loss, especially surgical weight loss, and its effect on cancers. To begin, I would like to acknowledge and congratulate all breast cancer survivors and let patients currently undergoing treatment know that you are all in my thoughts and prayers.

I think we often overlook the significant association of obesity and cancer, especially in postmenopausal women with breast cancer. The International Agency for Research on Cancer has determined, based on epidemiological studies, that people with obesity are at increased risk of developing several types of cancer, including adenocarcinoma of the esophagus, colon cancer, breast cancer (in postmenopausal women), endometrial cancer, and renal cell cancer.1 There is also evidence that liver, gallbladder, prostate, and pancreatic cancers are associated to obesity as well. Interestingly, there has not been any association between lung cancer and obesity to date.

The driving force for this strong association seems to be insulin resistance (IR). IR develops as a metabolic adaptation to increased levels of circulating free fatty acids released from adipose tissue, especially visceral adipose tissue. IR, in turn, produces increased insulin secretion, and this chronic hyperinsulinemia might increase the risk of the cancer, especially colon and endometrial cancer. In addition to hyperinsulinemia, elevated circulating levels of estrogen, also seen with increased adiposity, has been linked to postmenopausal breast and endometrial cancers.

The great news is, weight loss, especially surgical weight loss, significantly decreases the development certain types of cancers. In a 2018 British Journal of Surgery cohort study of nearly 9,000 patients, those who underwent some type of bariatric surgery had a 77-percent decreased risk of developing hormone-related cancers (breast, endometrial, or prostate) compared to nonbariatric surgery-matched controls.2 Curiously, however, patients who underwent gastric bypass experienced the largest reduction (84%) in hormone-related cancers, but it was also associated with a greater-than-two-fold increased risk of colorectal cancer. Additional studies are ongoing to understand the biological mechanisms behind these findings.

In summary, obesity is strongly associated with many types of cancers. Weight loss, especially surgical weight loss, has been shown to significantly decrease several hormone-related cancers. Additional studies are ongoing to understand the biological mechanisms associated with weight loss and the increased risk of colorectal cancer. Again, congratulations to all the breast cancer survivors and to all the patients battling cancer. You remain in our thoughts and prayers!


Christopher D. Still, DO, FACN, FACP


  1. Calle EE, Kaaks R. Overweight, obesity and cancer: epidemiological evidence and proposed mechanisms. Nat Rev Cancer. 2004;4:579–591.
  2. Mackenzie H, Markar SR, Askari A, et al. Obesity surgery and risk of cancer. Br J Surg. 2018;105(12):1650–1657.

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