Energy flux, more so than energy balance, protein intake, or fitness level, influences insulin-like growth factor-I system responses during 7 days of increased physical activity

• Published in: Journal of applied physiology (1985) Vol. 103; no. 5; pp. 1613 - 1621
• Main Authors: Rarick, Kevin R, Pikosky, Matthew A, Grediagin, Ann, Smith, Tracey J, Glickman, Ellen L, Alemany, Joseph A, Staab, Jeffery S, Young, Andrew J, Nindl, Bradley C
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.11.2007; American Physiological Society
• Subjects: Biochemistry; Biological and medical sciences; Body Composition; Carrier Proteins - blood; Diet; Dietary Proteins - metabolism; Energy balance; Energy Metabolism; Exercise; Fundamental and applied biological sciences. Psychology; Glycoproteins - blood; Humans; Insulin; Insulin-Like Growth Factor Binding Protein 1 - blood; Insulin-Like Growth Factor Binding Protein 2 - blood; Insulin-Like Growth Factor Binding Protein 3; Insulin-Like Growth Factor Binding Proteins - blood; Insulin-Like Growth Factor I - metabolism; Male; Motor Activity - physiology; Nutrition; Nutritional Physiological Phenomena; Oxygen Consumption; Physical Fitness - physiology; Proteins; Time Factors; Physical exercise; Insulin like growth factor binding protein; insulin-like growth factor binding proteins; Energy balance; Vertebrata; Physical fitness; Mammalia; exercise; Insulin like growth factor 1; nutritional factors
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00179.2007

1 Military Performance Division and 2 Military Nutrition Division, U. S. Army Research Institute of Environmental Medicine, Natick, Massachusetts Submitted 19 February 2007 ; accepted in final form 13 August 2007 The purpose of this study was to determine the impact of dietary factors and exercise-associated factors on the response of IGF-I and its binding proteins (IGFBPs) during a period of increased physical activity. Twenty-nine men completed a 4-day ( days 1–4 ) baseline period of a controlled energy balanced diet while maintaining their normal physical activity level followed by 7 days ( days 5–11 ) of a 1,000 kcal/day increase in physical activity above their normal activity levels. Two subject groups, one sedentary (Sed, mean O 2peak : 39 ml·kg –1 ·min –1 , n = 7) and one fit (FIT1, mean O 2peak : 56 ml·kg –1 ·min –1 , n = 8) increased energy intake to maintain energy balance throughout the 7-day intervention. In two other fit subject groups (FIT2, n = 7 and FIT3, n = 7), energy intake remained at baseline resulting in a 1,000 kcal/day exercise-induced energy deficit. Of these, FIT2 received an adequate protein diet (0.9 g/kg), and FIT3 received a high-protein diet (1.8 g/kg). For all four groups, IGF-I, IGFBP-3, and the acid labile subunit (ALS) were significantly decreased by day 11 (27 ± 4%, 10 ± 2%, and 19 ± 4%, respectively) and IGFBP-2 significantly increased by 49 ± 21% following day 3 . IGFBP-1 significantly increased only in the two negative energy balance groups, FIT2 (38 ± 6%) and FIT3 (46 ± 8%). Differences in initial fitness level and dietary protein intake did not alter the IGF-I system response to an acute increase in physical activity. Decreases in IGF-I were observed during a moderate increase in physical activity despite maintaining energy balance, suggesting that currently unexplained exercise-associated mechanisms, such as increased energy flux, regulate IGF-I independent of energy deficit. insulin-like growth factor binding proteins; exercise; nutritional factors Address for reprint requests and other correspondence: B. C. Nindl, Military Performance Division, U. S. Army Research Institute of Environmental Medicine, Natick, MA 01760 (e-mail: bradley.nindl{at}us.army.mil )