Second Opinion: Do You Know About Obesity's Link to Cancer?

Health Writer

Editor’s Note: This article is a part of an Op-Ed series, “Second Opinion,” where patient experts share their take on current research, news, and trends in health and medicine. The views expressed in this article do not reflect the opinions or views of

A 2016 United Kingdom survey found that 75 percent of people in the UK do not know that obesity is a risk factor for cancer. The survey also found that people from lower socioeconomic backgrounds were less likely to know about the link, and the survey findings suggest a general lack of knowledge about the specific cancers linked to obesity.

Because I’m a physician assistant with a special interest in lifestyle, I know that it’s likely that the U.S. population parallels the UK populace in terms of this lack of knowledge. Kalust Ucar, M.D., an oncologist who practices in Glendale, California, confirmed by email interview the possibility that we are pacing with the UK on this topic. He suggested that the problem with obesity is that “patients and doctors don’t see it as an urgent issue that will cause cancer with immediacy.”

I also know from personal patient care experience that if a patient presents with obesity, the conditions they worry about most are typically diabetes or heart disease, rather than cancer.

Fact sheets from the National Cancer Institute (NCI), including Obesity and Cancer RiskObesity and Cancer Prevention and Uncovering the Mechanism Linking Obesity and Cancer Risk, delineate the extensive research and current science suggesting the strong link between significant excess weight and cancer risk. Cancers on the list include postmenopausal breast cancer, endometrial, colorectal, esophageal, gallbladder, kidney, pancreatic, and thyroid cancers.

In 2002, the International Agency for Research on Cancer used European data and estimated (back then) that obesity contributed to more than one third of endometrial and esophageal cancer cases, and up to a quarter of kidney cancer cases. A 2003 New England Journal of Medicine review of data from the American Cancer Society suggested that 14 percent of cancer deaths in men and 20 percent of cancer deaths in women “could be blamed on excess weight.”  More recent studies on obese patients who have had bariatric surgery suggest lower rates of obesity-related cancers after surgery.

This subject is especially dear to my heart because my mother died at 63 after a one-year battle with aggressive breast cancer. She was postmenopausal, had a long history of obesity, and also had used hormone therapy for many years — a “perfect storm" for a significantly heightened risk for breast cancer. My dad was diagnosed with early kidney cancer in his seventies, and though he was always careful with his weight and lifestyle choices, he became even more so after a partial nephrectomy. My husband, a physician coincidentally, also was diagnosed with early kidney cancer, and after similar surgery, has struggled with his lifestyle habits. An exercise devotee, his BMI is still in the overweight range. Weight management, even in the face of a serious illness, can be confounding — even for a doctor.

I share these personal details because, while I do think being informed is crucial to one’s health, I’m not quite clear on when the information does and does not help. Obesity is often accompanied by denial. And I wonder just how many primary care doctors and specialists routinely discuss cancer when they discuss the dangers that obesity poses.

According to the NCI, more than 1.6 million people in the U.S. will be diagnosed with cancer by this year’s end. After smoking, obesity is considered the most modifiable risk factor for limiting cancer (and other chronic diseases). In our email interview, Dr. Ucar indicated that the conversation needs to occur between patient and primary care physician. But when he is consulted as a specialist, he suggests to the patient that “cancer and extra fat in the body is a bad mix." He added that, "Obesity heightens both risk for cancer and cancer recurrence.” He also acknowledged that obesity is more prevalent among poor and underprivileged individuals, the same people who often struggle with a lack of affordable healthcare coverage and ready access to healthcare, as well as irregular screenings and checkups.

Dr. Ucar notes that by looking at obesity as an isolated risk factor in this population, we may be introducing selective bias. Clearly these other issues also heighten obese patients’ risk for cancer.

In an interview posted on the NCI website, Walter Willet, M.D., chair of the department of nutrition at the Harvard School of Public Health and a noted authority on weight and diet, suggests that we continue to concern ourselves with carcinogens in foods and certain types of fat in our diets, as linked to cancer risk. Yet the link between excess weight and cancer, especially when obesity starts at a young age, is still taking time to disseminate and be taken seriously, among healthcare providers and the community at large. Pediatricians likely discuss the risk of prediabetes and hypertension associated with childhood obesity, but I wonder how often that cancer is part of the discussion, even though there is evidence that suggests the worrisome link?

In my conversations with other medical professionals, I have learned about the positive impact physicians can have in talking to their patients about the risks of obesity. In one such case, a patient who managing obesity characterized as morbid, was also a smoker. The patient’s six week follow-up visit revealed that she had stopped smoking and shed 20 pounds. However, the patient told her doctor that she thought he had been uncaring because he had told her to stop losing weight without seeming to understand how difficult it was to do. But she did stop smoking and she did lose weight. I don’t know if this doctor in particular mentioned the risk of lung cancer in the conversation, but I do know that he helped his patient to begin limiting her risk for a number of serious health conditions, including cancer. And that's a good thing.

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