Effect of protein supplementation during a 6-mo strength and conditioning program on insulin-like growth factor I and markers of bone turnover in young adults.
BACKGROUND
Exercise is beneficial for bone when adequate nutrition is provided. The role of protein consumption in bone health, however, is controversial.


OBJECTIVE
The objective was to ascertain the effect of high protein intake on insulin-like growth factor I (IGF-I) and markers of bone turnover during 6 mo of exercise training.


METHODS
Fifty-one subjects aged 18-25 y (28 men, 23 women) received a protein supplement (42 g protein, 24 g carbohydrate, 2 g fat) or a carbohydrate supplement (70 g carbohydrate) twice daily. Exercise consisted of alternating resistance training and running 5 times/wk. Plasma concentrations of IGF-I, insulin-like growth factor-binding protein 3, serum bone alkaline phosphatase, and urinary N-telopeptide collagen crosslink (NTx) concentrations were measured at 0, 3, and 6 mo after 24 h without exercise and a 12-h fast.


RESULTS
Three-day diet records indicated no difference in energy intake between the groups. Average protein intakes after supplementation began in the protein and carbohydrate groups were 2.2 +/- 0.1 and 1.1 +/- 0.1 g/kg, respectively (P < 0.001). The increase in plasma IGF-I was greater in the protein group than in the carbohydrate group (time x supplement interaction, P = 0.01). There were no significant changes over time or significant differences by supplement in plasma insulin-like growth factor-binding protein 3 (44 and 40 kDa). Serum bone alkaline phosphatase increased significantly over time (P = 0.04) and tended to be higher in the protein group than in the carbohydrate group (P = 0.06). NTx concentrations changed over time (time and time squared; P < 0.01 for both) and were greater in the protein group than in the carbohydrate group (P = 0.04). Men had higher NTx concentrations than did women (74.6 +/- 3.4 and 60.0 +/- 3.8 nmol/mmol creatinine; P = 0.005).


CONCLUSIONS
Protein supplementation during a strength and conditioning program resulted in changes in IGF-I concentrations.
Ballard
Tasha Lp
TL
Applied Physiology Laboratory, South Dakota State University, Brookings, SD 57007, USA.
Clapper
Jeffrey A
JA
Specker
Bonny L
BL
Binkley
Teresa L
TL
Vukovich
Matthew D
MD
D000293:Adolescent; D000328:Adult; D000469:Alkaline Phosphatase / Q000097:blood; D000704:Analysis of Variance; D015415:Biomarkers / Q000097:blood; D015519:Bone Density / Q000187:drug effects*; D001862:Bone Resorption; D001842:Bone and Bones / Q000378:metabolism*; D003094:Collagen / Q000652:urine; D024042:Collagen Type I; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000378:metabolism; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000378:metabolism; D005215:Fasting; D005260:Female; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000187:drug effects / Q000378:metabolism*; D008137:Longitudinal Studies; D008297:Male; D010455:Peptides / Q000652:urine; D010809:Physical Fitness / Q000502:physiology*; D012737:Sex Factors; D014891:Weight Lifting / Q000502:physiology*
D015415:Biomarkers; D024042:Collagen Type I; D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D018972:Insulin-Like Growth Factor Binding Protein 3; D010455:Peptides; C052929:collagen type I trimeric cross-linked peptide; D007334:Insulin-Like Growth Factor I; D003094:Collagen; D000469:Alkaline Phosphatase