One of the stated goals of the STOP Obesity Alliance is to identify, implement, and evaluate strategies to increase physical activity for patients with obesity. We renewed our commitment to promoting physical activity when we updated our organizational goals at the beginning of this year. Currently, physical inactivity is responsible for one in 10 deaths in U.S. adults. Over the last 50 years, occupational energy expenditure has decreased by more than 100 calories per day, which accounts for a significant portion of increased body weight in U.S. men and women.
Earlier this month, the Institute of Medicine's (IOM) Roundtable on Obesity Solutions hosted a public workshop exploring the role of physical activity in the prevention and treatment of obesity. The workshop also provided examples of innovative strategies for promoting physical activity. The two-day workshop was recorded and can be viewed on the IOM website, along with each of the speaker's PowerPoint presentations.
While I encourage you to explore the program in its entirety, several presentations are worth emphasizing. In his keynote address, Jim Hill reviewed several studies investigating adjustments in response to increased physical activity. A systematic review found that prescribed physical activity-like exercise training does not lead to significant decreases in non-exercise physical activity. Another meta-analysis found that individuals tend not to alter food intake in the immediate hours following exercise. These two reviews provide sound support for the conclusion that individuals neither increase sedentary behavior to compensate for increased physical activity nor do they increase food intake to compensate for increased energy expenditure. As a result, when individuals engage in moderate to vigorous physical activity (MVPA), they likely are able to prevent weight gain and improve body composition.
The type of physical activity may be less important. A newly published randomized control trial in the Journal of Applied Physiology compared the impact of a hypocaloric diet plus four different types of exercise: endurance training, strength training, endurance plus strength training and physical activity alone. Weight loss and changes in body composition were comparable in all four arms of the study.
In a discussion on childhood obesity, Dr. Kathleen Janz reviewed results from the Iowa Bone Development Study, a longitudinal study of 500 children that used accelerometers to measure physical activity. Over the course of 16 years, beginning at age 5, these children received eight follow-up exams. Sedentary time did not appear to affect adiposity measured by dual-energy X-ray absorptiometry (DEXA). MVPA was associated with a lower increase in adiposity and television time increased adiposity. These results emphasize the powerful effects of physical activity on the prevention of obesity in children. Consistent with other data, these observations also suggest that the impact of TV time on obesity is not mediated by the displacement of physical activity but more likely results from the influence of television on food intake, promoted by food advertising directed at children.
Dr. Ulf Ekelund discussed the role of physical activity in the prevention of obesity in adults. In a cohort of almost 300,000 participants from 10 European countries studied over five years, increased physical activity had a significant inverse effect on waist circumference, which would reduce the likelihood of several comorbidities. Baseline physical activity was not associated with a change in body weight after adjustment for age, baseline body weight, smoking, energy intake, alcohol consumption, education level, and duration of follow-up. Overall, physical activity was associated with a lower risk of the development of obesity in younger individuals at a normal weight. Other data indicate that increases in physical activity are associated with decreases in waist circumference without changes in body weight, indicating that physical activity improves body composition at the same body weight. Clothes will fit better but weight will not change. These results suggest that patients and the public may be better served by emphasizing the health benefits of physical activity and its effects on body composition rather than the effects of physical activity on body weight.
I suspect that these effects of physical activity are not widely known among primary care providers, and perhaps even among those who specialize in the treatment of obesity. Therefore, our challenge is to disseminate this information to those who need it. That task has begun with this newsletter, and could be enhanced by reviewing the workshop online.