Physical Activity and Weight Loss Maintenance

Excerpt

Obesity is a significant and increasing health problem worldwide. It is defined as a body mass index (BMI) of >30kg/m2 or >25kg/m2 with obesity-related comorbidity. Obesity is associated with increased morbidity and mortality, primarily through increased risk of cardiovascular disease, hypertension, and diabetes mellitus (DM). Reduced levels of physical activity (PA) are associated with obesity. Furthermore, it is independently associated with an increased risk of cardiovascular disease. In general, obesity occurs in response to variable environmental, psychological, and physical factors in genetically susceptible patients.

In simplest terms, weight change depends on the balance between energy intake and energy expenditure. However, this relationship is non-linear and involves many variables such as body mass composition, energy partition, and energy storage. In addition, variables such as baseline metabolism, cardiovascular fitness, lean muscle mass, and body mass all modify energy expenditure associated with PA. The physiologic response to weight loss strategies is an attempt to maintain body weight. Thus, attempts to lose weight through calorie restriction or increased PA trigger responses such as increased appetite and metabolic adaption to minimize net energy loss.

Weight change in patients with obesity is a complex multifactorial problem. Weight loss itself decreases the energy required and thus expenditure to perform equivalent PA activities after weight loss. Negative feedback circuits have been shown to influence food intake by increasing appetite and decreasing satiety. In addition to physiological variables, behavioral and psychological influences are extremely important to consider when treating patients.

Weight loss is the primary treatment for patients with obesity. While some improvement in cardiovascular risk has been demonstrated with a weight loss of 2 to 3%, clinical guidelines recommend a weight loss of 5% to 10% over 6 months to produce significant improvements in cardiovascular risk factors. However, maintenance of weight loss has traditionally been extremely difficult for patients with obesity. In 1959, Stunkard and McLaren-Hume showed that only 2% of 100 patients with obesity maintained significant weight loss at 2 years. More recently, in 2005, Wing and Phelan showed that 80% of 4000 patients in the National Weight Control Registry failed to maintain weight loss after 1 year. Although sustained weight loss is the target, many factors, including cardiovascular fitness and body mass composition, require consideration when treating patients with obesity.