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.
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 Vo(2peak): 39 mlxkg(-1)xmin(-1), n = 7) and one fit (FIT1, mean Vo(2peak): 56 ml.kg(-1)xmin(-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.
Rarick
Kevin R
KR
Military Performance Division, U. S. Army Research Institute of Environmental Medicine, Natick, MA 01760, USA.
Pikosky
Matthew A
MA
Grediagin
Ann
A
Smith
Tracey J
TJ
Glickman
Ellen L
EL
Alemany
Joseph A
JA
Staab
Jeffery S
JS
Young
Andrew J
AJ
Nindl
Bradley C
BC
D001823:Body Composition; D002352:Carrier Proteins / Q000097:blood*; D004044:Dietary Proteins / Q000378:metabolism*; D004734:Energy Metabolism; D006023:Glycoproteins / Q000097:blood*; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000097:blood; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000097:blood; D018972:Insulin-Like Growth Factor Binding Protein 3; D018969:Insulin-Like Growth Factor Binding Proteins / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009747:Nutritional Physiological Phenomena; D010101:Oxygen Consumption; D010809:Physical Fitness / Q000502:physiology*; D013997:Time Factors
D002352:Carrier Proteins; D004044:Dietary Proteins; D006023:Glycoproteins; C032231:IGFBP1 protein, human; C515497:IGFBP3 protein, human; D018970:Insulin-Like Growth Factor Binding Protein 1; D018971:Insulin-Like Growth Factor Binding Protein 2; D018972:Insulin-Like Growth Factor Binding Protein 3; D018969:Insulin-Like Growth Factor Binding Proteins; C075944:insulin-like growth factor binding protein, acid labile subunit; D007334:Insulin-Like Growth Factor I