Obesity Increases Cancer Risk and May Affect Treatment

With the easy availability of plentiful, inexpensive, and often unhealthy food, many of us work hard to avoid packing on the pounds. But our vigilance can waver, as seen in the growing numbers of obese American adults and children. In 1980, only one in seven Americans were obese, defined as having a body mass index, or BMI, of 30 or higher. Today, one in three are obese.


American Cancer Society guidelines for controlling weight include at least 150 minutes a week of moderate-intensity activity, such as brisk walking.

While most people are aware of the increased risk of cardiovascular disease and diabetes that comes with being obese, fewer than half of Americans understand that extra weight also increases their risk for certain types of cancer. And the risk can be significant: Obese women with breast cancer are 35 percent more likely than normal-weight women to die of their cancer, according to an analysis of more than 80 breast cancer studies reported in the Annals of Oncology online earlier this year. And obesity has been linked to a higher risk for cancer recurrence. A study published in the Journal of the National Cancer Institute in 2006 found a 38 percent increased risk of cancer recurrence or a new cancer among very obese cancer survivors (a BMI of 35 or higher) compared with normal-weight survivors.

Being obese also can affect cancer treatment. For example, some doctors give their obese patients smaller doses of chemotherapy than recommended for their weight, fearing that larger doses would be too toxic, but that decision could reduce the treatment’s effectiveness. Such “dose capping” was eliminated at many institutions after the American Society of Clinical Oncology released guidelines in 2012 that warned against the practice and advised oncologists to use body weight to calculate chemo doses.

Last year the American Medical Association recognized obesity as a disease. Some would call it an epidemic. By eating reasonable amounts of healthy foods, staying active, and controlling our weight, we can do our part to stem the tide of obesity. The American Cancer Society (ACS) offers simple guidelines for controlling weight. These include eating at least 2½ cups of vegetables and fruits a day, limiting processed and red meats, and replacing refined grain products with whole grains. For exercise the ACS recommends at least 150 minutes a week of moderate-intensity activity, such as brisk walking, or 75 minutes of vigorous-intensity activity, such as jogging or fast cycling.

You can read more about obesity and cancer risk and how being obese can effect cancer treatment in the fall issue of Cancer Today.