Obesity Epidemic Setting Stage for Cancer Upsurge, Scientists Warn

WASHINGTON, DC—A worldwide epidemic of obesity is setting the stage for marked increases in the incidence of many cancers, dietary experts warned here at the annual International Research Conference on Food, Nutrition, and Cancer. At the conference, sponsored by the American Institute for Cancer Research (AICR) and the World Cancer Research Fund International (WCRFI), scientists presented new evidence showing that obesity produces hormonal and metabolic changes that raise cancer risk. The AICR also released new nutrition guidelines for cancer survivors. “We are living in an extraordinary new time,” said Professor W.P.T. James, Chairman of the International Obesity Task Force in London. “The big worry that we've got is what's going to happen to cancer rates in the world.” Professor James cited research estimating that being overweight and inactive accounts for one quarter to one third of worldwide cases of cancers of the breast, colon, endometrium, kidney, and esophagus—between 102,000 and 135,000 people in the US alone. Today, he said, “the whole world is getting fatter,” even in developing nations. As a result, “we are suddenly confronting an enormous battle. There are massive epidemics of disease which are preventable,” including “a huge burden from cancers.” Scientists at the meeting expressed alarm at the findings of a new AICR survey of 1,025 Americans, which showed that only 25% of respondents realize that being overweight or obese raises the risk of cancer. Prof. James estimated that one billion people worldwide are overweight (body mass index over 25), and of those, 300 million are obese (body mass index over 30). In the US, 61% of the population is obese or overweight, according to the Office of the Surgeon General. But most Americans don't make the obesity/cancer link. Scientists at the meeting expressed alarm at the findings of a new AICR survey of 1,025 Americans, which showed that only 25% of respondents realize that being overweight or obese raises the risk of cancer. In contrast, 89% said being overweight is a risk factor for heart disease, and 86% said being overweight is a risk factor for diabetes. When asked a separate question about major risk factors for cancer, only 6% cited being overweight. In contrast, they cited exposure to certain chemicals (22%), high-fat diets (18%), sun exposure (18%), and family history (11%), among others. “If we lost weight, the nation's health would improve and there would be less cancer,” said George A. Bray, MD, Professor of Medicine at Louisiana State University Medical Center and the Pennington Biomedical Research Center. New Scientific Concept of Fat Cells Dr. Bray said the new scientific concept of fat cells indicates that they are remarkably active, behaving like endocrine cells, and constantly producing and secreting hormones and growth factors into the bloodstream. “What we now know is that fat cells are one of the most active secretory organs in the body,” he said. They produce more than 25 different chemicals, he noted. These secreted substances—sex hormones, insulin, and insulin-like growth factors—send signals to other parts of the body, and when they do so they set the stage for the initiation and growth of cancer cells. While the secreted substances are not in themselves harmful, he said, the fat cells in an overweight person appear to produce excessive amounts of these chemicals, thus apparently triggering the cells to grow and divide at an accelerated rate. When cell division and replication occur more rapidly, there is an increased risk of a random cell mutation that could ultimately lead to cancer, he said. Question about HRT Asked if there is a particular cancer risk for overweight postmenopausal women taking hormone-replacement therapy (HRT), given the new recognition of fat cells' role in the cancerous process and recent findings from the Women's Health Initiative (WHI) study, Dr. Bray said that the combination of estrogen and progestin in healthy postmenopausal women is “clearly detrimental on balance,” and that women on that HRT regimen should consult their doctors. The National Institutes of Health stopped the arm of the WHI designed to assess the risks and benefits of combined estrogen and progestin in healthy menopausal women early, due to an increased risk of invasive breast cancer. In this study arm, scheduled to run until 2005, there was a 26% increase in breast cancer risk among women taking combined estrogen and progestin. The Role of Exercise Obesity and inactivity often go hand in hand in increasing cancer risk, said Christine Friedenreich, PhD, Research Scientist/Epidemiologist in the Division of Epidemiology, Prevention & Screening at the Alberta Cancer Board in Canada and Adjunct Associate Professor of Community Health Sciences at the University of Calgary. Prof. James cited research estimating that being overweight and inactive accounts for 25% to 33% of worldwide cases of cancers of the breast, colon, endometrium, kidney, and esophagus—between 102,000 and 135,000 people in the US alone. “Exercise is coming into its own as a primary means of preventing cancer and improving cancer survival,” she said. Exercise seems to help regulate the hormones and growth factors that have been associated with cancer risk, she explained, noting that evidence for a protective effect is most convincing for breast and colon cancers. Exercise can decrease the overproduction of sex hormones linked to an increased risk of breast cancer, and that exercise likely reduces the risk of colon cancer because it speeds the transit of foods and decreases bile acids. In an interview, Dr. Bray said obesity is a “stigmatized problem,” and that the stereotype of blaming overweight people for being weak-willed runs through the medical profession as well as the general public. “Doctors are a mirror of the public; they're no better and no worse,” he said. “I'm pleased to see the AICR taking this [topic] on this year.” New Nutrition Guidelines for Cancer Survivors At the conference, the American Institute for Cancer Research released new guidelines to help cancer survivors eat in a healthy way. Ritva R. Butrum, PhD, AICR Vice President for Research and a panel member, explained that the guidelines were formulated by a panel of six dietary experts in response to a huge number of questions about diet from cancer survivors and a desire to help them turn to foods and not rely on large amounts of dietary supplements. The guidelines are as follows: Choose predominantly plant-based diets rich in a variety of vegetables and fruits. If eaten at all, limit red meat to less than three ounces daily. Limit consumption of fatty foods, especially those of animal origin, and use modest amounts of vegetable oils. Limit consumption of salted foods, salt in cooking, and table salt. Limit alcohol to less than two drinks a day for men and one for women. Do not eat charred food, and only occasionally eat meat and fish grilled on a direct flame and cured and smoked meats. Avoid being overweight and limit weight gain in adulthood. Take an hour's brisk walk or similar exercise daily. Novel Approach to Weight Loss It has already been demonstrated that angiogenesis inhibitors can shrink tumors. Now, an instructor in medicine at Brigham & Women's Hospital has found that the drugs can shrink fat as well. In studies conducted on so-called ob/ob mice, overweight animals that weigh at least twice as much as normal mice, Maria Rupnick, MD, PhD, found that they lost considerable amounts of weight when given angiogenesis inhibitors. She undertook a study of the vascular structure of fat after hypothesizing that the inhibitors might have an effect on fat as well as blood supply. She noted that adipose tissue is the only noncancerous tissue in the body that grows and regresses, based on caloric intake. Working with TNP-460, angiostatin, endostatin, and other angiogenesis inhibitors, Dr. Rupnick found that ob/ob mice and other obese mice lost a considerable amount of weight. She theorized that the reason for the weight loss was that the drugs decreased their appetites and the mice were using the fat as fuel. “If that fat goes into their blood stream—which is where it has to go because it has to go somewhere—it gets converted into fatty acids and other things that can be used as a fuel,” Dr. Rupnick told The New York Times. “So the animal essentially consumes its own fat for energy.” She also reported that she found no evidence of toxicity. Dr. Rupnick has a patent covering the commercial application of her work. The patent was licensed to Repair, Inc., a Boston company. Angiogenesis pioneer Judah Folkman, MD, in whose laboratory she worked, was listed as a co-inventor.

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