At a time when nearly two-thirds of the U.S. population is considered overweight or obese, compelling evidence suggests that excess body weight is a risk factor for many cancers. However, in terms of weight-related factors, body weight alone does not completely determine an individual's ability to prevent or survive cancer. Instead, cancer researchers use the term "energy balance" to describe the complex interaction among diet, physical activity, and genetics on growth and body weight over an individual's lifetime and how those factors may influence cancer risk.

NCI has supported epidemiologic research in large cohort and case-control studies looking at the effects of weight, diet, physical activity, and cancer outcomes. These and other studies suggest that being overweight or obese increases the risk for postmenopausal breast cancer, colon cancer, adenocarcinoma of the esophagus, endometrial cancer, renal cell carcinoma, and several other cancers. Other studies, including some basic animal and cell culture studies, have explored the mechanisms by which obesity may influence cancer risk. Clinical intervention studies involving small groups of patients have placed people on specific diet, activity, and weight-control regimens to see how those factors influence cancer risk. This research is promising and should yield great insights into how these particular behavioral and genetic factors contribute to the cancer burden.

As is often the case, this research has raised as many questions as it has answered. It is abundantly clear, however, that regular physical activity can reduce the risk of colon cancer by half, and can also reduce the risk of breast cancer among obese postmenopausal women. Additionally, we know that balancing "energy in/energy out" - the calories eaten vs. those burned each day - is imperative to avoid gaining weight. For many Americans who are overweight and sedentary, eating fewer calories and increasing physical activity is necessary to reach a healthy weight.

The nation's obesity epidemic has heightened our interest in obesity and energy balance at both NIH and NCI. In 2002, NCI formed a group to identify priorities for obesity and cancer research. The group identified three goals: to understand the causes of adverse patterns of weight, physical activity, and diet; define how these causes contribute to cancer; and apply this knowledge to prevent and control cancer. We hope to understand how obesity can interact over the entire lifetime to influence the cancer process, and to develop better measures of weight, diet, and physical activity. To do this, NCI will continue to work actively with NIH and other federal and private partners to complement and extend existing efforts.

In 2005, NCI anticipates receiving funding for transdisciplinary centers on energetics and cancer. The centers will bring together scientists from multiple disciplines to accelerate progress toward reducing cancer incidence, morbidity, and mortality associated with obesity, low levels of physical activity, and poor diet. The centers also will provide significant opportunities to train scientists at every stage in their careers in the area of energy balance and cancer. NCI is also now developing an energy balance intervention dissemination initiative to actively disseminate evidence-based interventions for obesity.

I invite you to learn more about NCI's energy balance initiative, including research plans and progress, in The Nation's Investment in Cancer Research: A Plan and Budget Proposal for Fiscal Year 2005 at: http://cancer.gov/pdf/nci_2005_plan.

Andrew C. von Eschenbach, M.D.
Director, National Cancer Institute