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This year, an estimated 1.47 million Americans will be diagnosed with cancer, and more than 562,000 will die of it. Two major classes of factors influence the incidence of cancer: hereditary and environmental. Hereditary factors, such as inherited genetic mutations, come from our parents and account for about 5 percent of all cancers.

Environmental factors, which include tobacco use, certain infectious agents, certain medical treatments, excessive sun exposure, and exposures to cancer-causing agents known as carcinogens that exist as pollutants in our air, food, water and soil, account for an estimated 75-80 percent of cancer cases and deaths. Obesity is also an environmental factor that is clearly associated with increased risk for developing many cancers, causing more than 100,000 cases of cancer in the U.S. each year, according to a recent study from researchers at the American Institute for Cancer Research (AICR).

Using findings from an AICR and World Cancer Research Fund report released earlier this year and the latest U.S. cancer incidence data, the researchers were able to calculate the exact percentage of specific cancers that are caused by excess body fat. Specifically, 49 percent of endometrial (uterine) cancers, approximately 20,700 cases, could be prevented if people maintained a healthy weight.

That number is followed by 35 percent, or 5,800 cases, of esophageal cancer; 28 percent, or 11,900 cases, of pancreatic cancer; 24 percent, or 13,900 cases, of kidney cancer; 21 percent, or 2,000 cases, of gallbladder cancer; 17 percent, or 33,000 cases, of breast cancer; and 9 percent, or 13,200 cases, of colon cancer. “This is the first time that we’ve put real, quantifiable case numbers on obesity-related cancers,” said Glen Weldon, the American Institute for Cancer Research educational director.

“We now know that carrying excess body fat plays a central role in many of the most common cancers,” said Dr. Laurence Kolonel, Deputy Director of the Cancer Research Center of Hawaii and AICR/WCRF expert panel member. He explains that fatty tissue, also known as adipose tissue, produces hormones that could play a role in promoting cancer cells. For instance, fat cells produce estrogen, which is now known to be a factor in breast and endometrial cancer.

Studies have also shown that being overweight reduces the effectiveness of the immune system. And Kolonel says not only does obesity increase the risk of cancer, it also makes treatment more difficult and has an adverse impact on survival.