Extra weight adds cancer risk.

• Position: Obesity

Researchers at the American Institute for Cancer Research (AICR) warn that carrying extra weight means carrying extra cancer risk. Moreover, the nation's current epidemic of overweight and obesity is likely to drive up cancer rates in coming years.

"This is a warning that needs to be heard," emphasizes Melanie Polk, AICR Director of Nutrition Education. "Most Americans know that obesity is related to cardiovascular disease and diabetes, but far fewer are aware that shedding pounds could reduce their risk of getting cancer."

In their review of the available evidence from laboratory, clinical, and large-scale epidemiological studies, the AICR researchers reached several conclusions about obesity's link to cancer at different sites:

Breast cancer is the most-common cancer among women in the U.S. Most of the studies that have looked at obesity and breast cancer have focused on postmenopausal breast cancer. Scientists believe that fat tissue exhibits one particular biological property that may play a significant role in cancer development.

According to the AICR researchers, it has long been established that, during a woman's reproductive years, the ovaries produce estrogen, a hormone that regulates the menstrual cycle and other sexual functions. Exposure to estrogen has been shown to stimulate the body's cells to reproduce more rapidly, which is associated with increased risk for cancer. Another source of estrogen is fat tissue, but the amount of estrogen produced by fat is much lower than that produced by the ovaries.

Although the ovaries stop secreting estrogen at menopause, studies have shown that fat tissue continues to pump the hormone (and other so-called "growth factors") into the bloodstream unabated. Thus, overweight and obese women continue to expose their bodies to estrogen's effects for as long they carry significant amounts of fat tissue. It is believed that this extended lifelong exposure to estrogen is linked to the increased breast cancer risk seen after menopause.

There is also support in the scientific literature for a link between a condition called insulin resistance and breast cancer (and, perhaps, cancer in general). Under normal circumstances, the pancreas produces low levels of insulin to help metabolize certain components of the diet--glucose and carbohydrates Studies have shown that, in overweight and obese individuals, the tissues of the body become less sensitive to insulin. As a result, these individuals have...