Accelerated Risk: Cancer and Obesity

For many people diagnosed with cancer, sudden unexplained weight loss is the first noticeable sign of the disease. Yet in the years after being diagnosed, approximately one-third of American cancer survivors are obese, and according to a new Mailman School study, rates of obesity in this group have climbed at a faster rate that the general population.

In an analysis of data from National Health Interview Surveys from 1997 to 2014, published in the Journal of Clinical Oncology, Heather Greenlee, assistant professor of Epidemiology, and colleagues found obesity prevalence in adults who have had a cancer diagnosis climbed from 22 to 32 percent compared with 21 to 30 percent for those with no history of cancer.

Perhaps it should come as no surprise that so many cancer survivors have elevated BMIs since obesity is a risk factor for some cancers, especially cancers that affect human metabolism, such as breast and colorectal cancers. At the same time, cancer treatments like some chemotherapy drugs, steroid medications, and anti-hormone therapy, promote weight gain.

“Breast cancer patients who go through chemotherapy and hormonal therapy will gain on average around 5 percent of their body weight,” says Greenlee, who studies diet, physical activity, and weight management for cancer survivors. “That’s not the typical picture people have of cancer patients wasting or unable to eat.” In fact, she says, today’s anti-nausea meds are very effective, and many cancer patients become more sedentary after being diagnosed. “They’re getting treatment, their mood may be low, and they’re not up and moving.”

Thanks to diagnostic and treatment advances, cancer survivors are living ever-longer lives. The added years, while certainly welcome, give survivors more time to put on weight. Meanwhile, obesity can raise risk for recurrence, and depending on the type of cancer, raise the risk of death. An elevated BMI is a risk for early death in breast cancer; whereas in other cancers, it may actually be protective. (A forthcoming paper by Greenlee explores the link between obesity and cancer survival in greater detail.)

Of course, the health consequences of obesity extend far beyond cancer. An elevated BMI is linked to life-threatening conditions such as diabetes, heart attacks, and stroke. In fact, more breast cancer survivors die from heart disease than metastatic cancer—all the more reason why preventing obesity in cancer survivors is so important.

“Maintaining weight or achieving a healthy weight, being physically active, eating a healthy diet: all these things can contribute to longer survival overall,” says Greenlee.

In the new paper, the researchers took a closer look at obesity trends in several specific cancers. Rates of obesity in colorectal cancer patients grew at a pace faster than cancer patients overall, particularly among young African-American women and older African-American men. Among breast cancer survivors, young white women saw the biggest gains. Prostate cancer survivors had obesity rates in line with those without a history of cancer. 

The American Cancer Society recommends that all cancer survivors eat a healthy diet, exercise 150 minutes a week, and maintain a healthy BMI. Yet according to Greenlee, many patients find the goals unattainable and easy to ignore. She hopes that the new information about who is most at risk for obesity will help target prevention efforts in and out of the doctor's office, adding that the knowledge might even help make the case to insurers to readily reimburse nutrition, physical activity and weight management counseling for cancer survivors.

“Obesity in cancer survivors is a growing public health problem hiding in plain sight,” says Greenlee. “We need to see it for what it is and develop effective ways to address it.”