Effects of dietary carbohydrate restriction with high protein intake on protein metabolism and the somatotropic axis

J Clin Endocrinol Metab. 2005 Sep;90(9):5175-81. doi: 10.1210/jc.2005-0559. Epub 2005 Jun 21.


Context: Alterations in dietary macronutrient intake can influence protein turnover.

Objective: The purpose of this study was to assess the influence of a low-carbohydrate/high-protein diet (LC/HP) on skeletal muscle protein synthesis and whole-body proteolysis, without the confounding influence of a negative energy balance.

Design: Nine-day dietary intervention was applied.

Setting: Subjects remained in the General Clinical Research Center throughout the 9-d study.

Participants: Eight young, healthy volunteers participated.

Intervention: Subjects ate a typical Western diet (60% carbohydrate, 30% fat, 10% protein) for 2 d, followed immediately by 7 d of an isocaloric LC/HP (5% carbohydrate, 60% fat, 35% protein).

Main outcome measures: Skeletal muscle fractional synthetic rate and whole-body proteolysis [leucine rate of appearance in plasma (Ra)] were measured after an overnight fast before and after 2 and 7 d of LC/HP. We also measured plasma concentrations of insulin, GH, and IGF-I.

Results: Leucine Ra was increased (P = 0.03) after 2 and 7 d of LC/HP, and muscle fractional synthetic rate was approximately 2-fold higher (P < 0.01) after 7 d of LC/HP. Fat free mass was not altered by LC/HP. Average 24-h plasma insulin concentration was 50% lower (P < 0.001) after 2 and 7 d of LC/HP, whereas GH secretion and total plasma IGF-I concentrations were unchanged with LC/HP. However, plasma free IGF-I decreased by approximately 30% after 7 d of LC/HP (P = 0.002), whereas muscle IGF-I mRNA increased about 2-fold (P = 0.05).

Conclusions: Increasing dietary protein content during a 7-d carbohydrate restricted diet stimulated muscle protein synthesis and whole-body proteolysis without a measurable change in fat free mass.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Caloric Restriction*
  • Dietary Carbohydrates / administration & dosage*
  • Dietary Proteins / administration & dosage*
  • Dietary Proteins / pharmacology
  • Dose-Response Relationship, Drug
  • Female
  • Growth Hormone / blood*
  • Humans
  • Insulin / blood
  • Insulin-Like Growth Factor I / genetics
  • Insulin-Like Growth Factor I / metabolism
  • Leucine / blood
  • Male
  • Muscle Proteins / biosynthesis
  • Muscle Proteins / metabolism*
  • Peptide Hydrolases / metabolism
  • Protein Biosynthesis / drug effects
  • RNA, Messenger / metabolism
  • Reference Values
  • Time Factors


  • Dietary Carbohydrates
  • Dietary Proteins
  • Insulin
  • Muscle Proteins
  • RNA, Messenger
  • Insulin-Like Growth Factor I
  • Growth Hormone
  • Peptide Hydrolases
  • Leucine