Physical Inactivity and Obesity is Not a Myth: Dr. Steven Blair Comments on the BJSM Editorial
An editorial published online this week in the British Journal of Sports Medicine claims that physical activity has virtually nothing to do with weight management. I respectfully disagree with many of the claims in the report.
The authors claim that physical activity does not promote weight loss. Similar points were made in another article by other authors published in 2013 (1), and my colleagues and I published a commentary showing the weaknesses of their interpretation of the data (2). If you are interested in the details, please review that commentary. More detailed information on many of these points is presented in a position statement from the American College of Sports Medicine (3).
A second flawed point in the editorial is that over the past 30 years there has been little change in physical activity, so the obesity epidemic must be due to increases in caloric intake. If one considers self-reported leisure-time physical activity over this period, there has been little change in these data in the U.S. However, leisure-time physical activity is only a small component of total daily energy expenditure. For example, most adults spend many hours a week on a job. Can anyone really believe that there has been no decline in occupational energy expenditure over the past several decades? My colleagues and I published a report in 2011 on this topic (4). I doubt that anyone will be surprised to learn that, according to data from the U.S. Department of Labor; mining, manufacturing, and agricultural jobs declined substantially; while sedentary service jobs had a huge increase. The decline in occupational energy expenditure over the past 50 years was 140 calories/day in men and 120 calories/day in women. When we did mathematical modeling and used these declines to predict the average weights of American women and men obtained in the National Health and Nutrition Examination Surveys over this period, the correlations between predicted weights from our model and the measured weights were extremely high. Another component of daily energy expenditure for adults is household management, which includes cleaning, cooking, child care, and other activities. We found that over the past several decades there has been a decline in this component of energy expenditure of 1800 calories/week in American women (5).
The authors of the editorial suggest that the obesity epidemic is due entirely to people eating too much. They present no data to support the claim that average daily caloric intake has increased. My colleagues and I performed extensive analyses of the dietary data collected in the National Health and Nutrition Surveys and found that the dietary data are simply implausible and that there is no firm evidence that Americans are eating any more calories/pound/day than they did decades ago (6). While we believe that energy intake is important for weight management, we think that declining energy expenditure is a critical contributor to the obesity epidemic and should not be ignored. We believe that in order to prevent weight gain, increases in energy expenditure are necessary.
Steven Blair serves on the scientific advisory boards of Clarity, Sports Surgery Clinic, Cancer Foundation for Life; and has received unrestricted research grants from the U.S. National Institutes of Health, U.S. Department of Defense; BodyMedia; Technogym; and The Coca-Cola Company. He receives book royalties from Human Kinetics.
Luke A, Cooper R. Physical Activity does not Influence Obesity Risk: Time to Clarify the Public Health Message. International Journal of Epidemiology; 2013; 42:1831-6.
Blair SN, Archer E, Hand GA. Luke and Cooper are wrong: physical activity has a crucial role in weight management and determinants of obesity. Int J Epidemiol, 2013;43:1836-8.
Donnelly JE, Blair SN, Jakicic JM, Manore MM, Rankin JW, Smith BK . American College of Sports Medicine Position Stand. Appropriate physical activity intervention strategies for weight loss and prevention of weight regain for adults. Med Sci Sports Exerc, 2009; 41:459-71.
Church TS, Thomas DM, Tudor-Locke C, Katzmarzyk PT, Earnest CP, Rodarte RQ, Martin CK, Blair SN, Bouchard C. Trends Over 5 Decades in U.S. Occupation- Related Physical Activity and their Associations with Obesity. Plos One, 2011; 6(5):1-7.
Archer E, Shook RP, Thomas DM, Church TS, Katzmarzyk PT, Hebert JR, McIver KL, Hand GA, Lavie CJ, Blair SN. 45-year trends in women's use of time and household management energy expenditure. PLOS One. 2013;8(2):e56620.
Archer E, Hand GA, Blair SN. Validity of U.S. nutritional surveillance: National Health and Nutrition Examination Survey caloric energy intake data, 1971-2010. PLOS One, 2013;8(10):e76632.