Increasing obesity, increasing challenges: The link between obesity and cancer

In brief, the relationship between excess weight and cancer incidence and survival is complex. On the one hand, a large body of research supports an association between increased risk of many types of cancer and excess weight, with considerable evidence of controlled experimental animal studies reporting much benefit from caloric restriction against cancer development and for longer survival. This suggests that efforts to unravel the complexity of obesity and cancer should be continued and increased. On the other hand, our understanding of the relationship between excess weight and cancer is severely challenged by our inability to subject humans to experimental conditions, even if they could maintain adherence to weight change protocols successfully, which is highly doubtful. As a result, studies among humans have been far less consistent or clear, which obfuscates our understanding of cancer risk, excess weight, weight loss, and weight cycling. That studies report differences by gender and type of canceronly adds complexity and challenge to understanding, as women and men are different biologically, and although different types of cancers share some characteristics, many have features unique to their own development. Thus, we are currently far from knowing whether and how weight loss directly reduces cancer risk or the impact of weight cycling either. The good news, however, is that the tools and technology available, as well as the knowledge already in hand, position investigators in the field well to make important discoveries in the future, hopefully sooner than later. As we work toward achieving our goal of primary prevention, it is important to encourage active secondary prevention strategies such as cancer screening and early detection, especially for obese individuals at greater risk.