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To the Editor: Dr Jakicic and colleagues¹ concluded that vigorous exercise intensity was not superior to moderate exercise intensity for weight loss in a 12-month physical activity program with additional restriction in dietary fat and caloric intake.

To help explain this unexpected finding, we suggest that the intensity-dependent effect of physical activity on body composition should be taken into account. A higher intensity level of physical activity leads to a more pronounced shift in the relationship of fat mass with fat-free mass (specifically, skeletal muscle mass) with only minimal changes in body weight.^2-3 Thus, the apparent lack of an effect of intensity may be due to higher postintervention fat-free mass in the individual who exercised vigorously. This potential benefit of higher exercise intensity could have been assessed with measurement of body composition.

Martin Ritt, MD; Monika Lechleitner, MD
Department of Internal Medicine
University Hospital Innsbruck
Innsbruck, Austria

1. Jakicic JM, Marcus BH, Gallagher KI, Napolitano M, Lang W. Effect of exercise duration and intensity on weight loss in overweight, sedentary women: a randomized trial. JAMA. 2003;290:1323-1330. FREE FULL TEXT 2. Garrow JS, Summerbell CD. Meta-analysis: effect of exercise, with or without dieting, on the body composition of overweight subjects. Eur J Clin Nutr. 1995;49:1-10. WEB OF SCIENCE | PUBMED 3. Grediagin A, Cody M, Rupp J, Benardot D, Shern R. Exercise intensity does not effect body composition change in untrained, moderately overfat women. J Am Diet Assoc. 1995;95:661-665. FULL TEXT | WEB OF SCIENCE | PUBMED

Letters Section Editor: Stephen J. Lurie, MD, PhD, Senior Editor.

JAMA. 2003;290:3069.

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