Lower extremity muscle size and strength and aerobic capacity decrease with caloric restriction but not with exercise-induced weight loss

1 Division of Geriatrics and Nutritional Sciences, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri; 2 Division of Biostatistics, Washington University School of Medicine, St. Louis, Missouri; 3 Division of Food Science, Human Nutrition and Health, Istituto Superiore di Sanitá, Rome, Italy; and 4 Cardiovascular Division, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri Submitted 2 August 2006 ; accepted in final form 2 November 2006 Caloric restriction (CR) results in fat loss; however, it may also result in loss of muscle and thereby reduce strength and aerobic capacity ( O 2 max ). These effects may not occur with exercise-induced weight loss (EX) because of the anabolic effects of exercise on heart and skeletal muscle. We tested the hypothesis that CR reduces muscle size and strength and O 2 max , whereas EX preserves or improves these parameters. Healthy 50- to 60-yr-old men and women (body mass index of 23.5–29.9 kg/m 2 ) were studied before and after 12 mo of weight loss by CR ( n = 18) or EX ( n = 16). Lean mass was assessed by dual-energy X-ray absorptiometry, thigh muscle volume by MRI, isometric and isokinetic knee flexor strength by dynamometry, and treadmill O 2 max by indirect calorimetry. Both interventions caused significant decreases in body weight (CR: –10.7 ± 1.4%, EX: –9.5 ± 1.5%) and lean mass (CR: –3.5 ± 0.7%, EX: –2.2 ± 0.8%), with no significant differences between groups. Significant decreases in thigh muscle volume (–6.9 ± 0.8%) and composite knee flexion strength (–7.2 ± 3%) occurred in the CR group only. Absolute O 2 max decreased significantly in the CR group (–6.8 ± 2.3%), whereas the EX group had significant increases in both absolute (+15.5 ± 2.4%) and relative (+28.3 ± 3.0%) O 2 max . These data provide evidence that muscle mass and absolute physical work capacity decrease in response to 12 mo of CR but not in response to a similar weight loss induced by exercise. These findings suggest that, during EX, the body adapts to maintain or even enhance physical performance capacity. diet; training; energy deficit; cardiovascular; sarcopenia Address for reprint requests and other correspondence: E. P. Weiss, Dept. of Nutrition and Dietetics, St. Louis Univ., 3437 Caroline St., Rm. 3076, St. Louis, MO 63104 (e-mail: eweiss4{at}slu.edu )