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


METHODS
Nine-day dietary intervention was applied.


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


METHODS
Eight young, healthy volunteers participated.


METHODS
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).


METHODS
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.
Harber
Matthew P
MP
University of Michigan, Division of Kinesiology, 401 Washtenaw Avenue, Ann Arbor, Michigan 48109-2208, USA.
Schenk
Simon
S
Barkan
Ariel L
AL
Horowitz
Jeffrey F
JF
D000328:Adult; D031204:Caloric Restriction; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D013006:Growth Hormone / Q000097:blood*; D006801:Humans; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism; D007930:Leucine / Q000097:blood; D008297:Male; D009124:Muscle Proteins / Q000096:biosynthesis / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D012016:Reference Values; D013997:Time Factors
D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D007328:Insulin; D009124:Muscle Proteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D010447:Peptide Hydrolases; D007930:Leucine