Exercise, Energy Balance and Cancer

Abstract

Energy balance in living organisms is a complex process in which energy input, determined by quantity and quality of caloric intake, is balanced by energy expenditure, which includes physical activity, exercise, and thermogenesis, with the processes being exquisitely regulated by environmental, physiologic and genetic influences, as well as by biobehavioral influences including appetite, satiety and sleep, to facilitate normal growth, development and function. Abnormalities in any aspect of these processes may result in underweight and malnutrition or overweight and obesity and a variety of comorbid conditions. Obesity can be associated with multiple comorbidities including diabetes, cardiovascular diseases and a variety of malignancies. In contrast, physical activity and exercise have been associated with prevention of these disorders and with beneficial effects in their therapy and outcomes. More specifically, physical activity and exercise are associated with reduced risk of some malignancies, with evidence considered convincing for colon cancer, probable for endometrial and post-menopausal breast cancer and limited for lung, and pancreatic cancers [1]. Carefully designed programs of moderate to aggressive physical activity and exercise in patients with cancer can lead to improved quality of life, reduced cancer related fatigue, improved cardiovascular fitness, reduced visceral fat mass and improved bone mineral density [2, 3]. Moreover, exercise has more recently been shown to improve both overall and, in some cases, cancer-specific survival [4]. Yet concern exists that exhaustive exercise may cause sufficient increase in oxidative stress to increase inflammation, impair immune function and allow for increased tumor growth [5, 6]. Thus, careful examination of the risks and benefits associated with exercise interventions and their potential mechanisms of action is a central theme in considerations of energy balance and cancer.