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

Am J Clin Nutr. 2005 Jun;81(6):1442-8. doi: 10.1093/ajcn/81.6.1442.


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.

Design: 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).

Conclusion: Protein supplementation during a strength and conditioning program resulted in changes in IGF-I concentrations.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Alkaline Phosphatase / blood
  • Analysis of Variance
  • Biomarkers / blood
  • Bone Density / drug effects*
  • Bone Resorption
  • Bone and Bones / metabolism*
  • Collagen / urine
  • Collagen Type I
  • Dietary Carbohydrates / administration & dosage
  • Dietary Carbohydrates / metabolism
  • Dietary Proteins / administration & dosage*
  • Dietary Proteins / metabolism
  • Fasting
  • Female
  • Humans
  • Insulin-Like Growth Factor Binding Protein 3 / blood
  • Insulin-Like Growth Factor I / drug effects
  • Insulin-Like Growth Factor I / metabolism*
  • Longitudinal Studies
  • Male
  • Peptides / urine
  • Physical Fitness / physiology*
  • Sex Factors
  • Weight Lifting / physiology*


  • Biomarkers
  • Collagen Type I
  • Dietary Carbohydrates
  • Dietary Proteins
  • Insulin-Like Growth Factor Binding Protein 3
  • Peptides
  • collagen type I trimeric cross-linked peptide
  • Insulin-Like Growth Factor I
  • Collagen
  • Alkaline Phosphatase