Negative energy balance plays a major role in the IGF-I response to exercise training.
Circulating IGF-I is correlated with fitness, but results of prospective exercise training studies have been inconsistent, showing both increases and decreases in IGF-I. We hypothesized that energy balance, often not accounted for, is a regulating variable such that training plus an energy intake deficit would cause a reduction in IGF-I, whereas training plus energy intake excess would lead to an increased IGF-I. To test this, 19 young, healthy men completed a 7-day strenuous exercise program in which they were randomly assigned to either a positive energy balance [overfed (OF), n = 10] or negative energy balance [underfed (UF), n = 9] group. IGF-I (free and total), insulin, and IGF-binding protein-1 were measured before, during, and 1 wk after the training. Weight decreased in the UF subjects and increased in the OF subjects. Free and total IGF-I decreased substantially in the UF group (P < 0.0005 for both), but, in the OF group, IGF-I remained unchanged. The UF group also demonstrated an increase in IGF-binding protein-1 (P < 0.027), whereas glucose levels decreased (P < 0.0005). In contrast, insulin was reduced in both the OF and UF exercise-training groups (P < 0.044). Finally, within 7 days of the cessation of the diet and training regimen, IGF-I and IGF-binding protein-1 in the UF group returned to preintervention levels. We conclude that energy balance during periods of exercise training influences circulating IGF-I and related growth mediators. Exercise-associated mechanisms may inhibit increases in IGF-I early in the course of a training protocol, even in overfed subjects.
Nemet
Dan
D
Center for the Study of Health Effects of Exeercise in Childdren, University of California Children's Hospital, College of Medicine, Irvine, CA 92868, USA.
Connolly
Peter H
PH
Pontello-Pescatello
Andria M
AM
Rose-Gottron
Christie
C
Larson
Jennifer K
JK
Galassetti
Pietro
P
Cooper
Dan M
DM
D000293:Adolescent; D000328:Adult; D001786:Blood Glucose; D001823:Body Composition; D001835:Body Weight; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006400:Hematocrit; D019382:Human Growth Hormone / Q000097:blood; D006801:Humans; D007328:Insulin / Q000097:blood; 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 / Q000097:blood; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000097:blood; D018976:Insulin-Like Growth Factor Binding Protein 6 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D010809:Physical Fitness; D012709:Serum Albumin
D001786:Blood Glucose; D007328:Insulin; D018970:Insulin-Like Growth Factor Binding Protein 1; D018971:Insulin-Like Growth Factor Binding Protein 2; D018972:Insulin-Like Growth Factor Binding Protein 3; D018974:Insulin-Like Growth Factor Binding Protein 4; D018976:Insulin-Like Growth Factor Binding Protein 6; D012709:Serum Albumin; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I