Researchers at the American Institute for Cancer Research (AICR) warned recently that carrying extra weight means carrying extra cancer risk. They added that the US nation's current epidemic of overweight and obesity is likely to drive up cancer rates in coming years. The researchers issued the warning after completing a review of existing scientific literature on the obesity-cancer link. This review found a rapidly growing number of studies showing that obesity is clearly a factor in some of the most common cancers in the U.S. "This is a warning that needs to be heard," said Melanie Polk, RD, 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 a recent AICR survey, only 35 per cent of Americans believed obesity to be linked to cancer. Yet over 60 per cent of Americans are overweight or obese, according to the Centers for Disease Control and Prevention. The AICR comprehensive analysis of the available science was motivated by the need to clarify and communicate the association between obesity and cancer. Researchers collected and analysed individual studies, review articles, international reports and white papers covering all aspects of obesity and cancer risk. The researchers distinguished between overweight and obesity, which are both commonly defined by a formula that combines height and weight measurements. An individual's Body Mass Index (BMI) is the ratio of weight (in kilograms) to height (in meters squared). A BMI between 18.5 and 25 is considered healthy. Between 25 and 30 is considered overweight, and above 30 is considered obese. Although the strongest evidence implicates obesity as a cancer risk, the AICR researchers noted that there is some consensus in the literature that overweight individuals also have higher cancer risk, and that cancer risk generally increases as BMI increases. The AICR researchers also stressed that because the area of obesity and cancer has only recently become the focus of widespread research, certain kinds of cancers have been studied more thoroughly than others. According to the researchers, evidence that obesity increases risk is most consistent for breast cancer in post-menopausal women. Results in regard to colon cancer have been more variable, but there is a general consensus that obesity presents an increased risk, particularly in men. Obese individuals are also clearly at increased risk for cancers of the endometrium (lining of the uterus), prostate and kidney. These are among the most common types of cancer in the US and the world. One other important factor that emerged from AICR's new analysis of the scientific literature is the central role that regular physical activity plays in reducing cancer risk. In an overwhelming majority of studies, exercise was consistently associated with lower risks for many different types of cancer.