Background: Malnutrition is common in hospitalized injured patients.
It contributes to delayed fracture-healing and increased morbidity. However,
relatively little attention has been directed toward nutritional strategies
for augmenting musculoskeletal recovery after a fracture. This animal study
was designed to examine the effects of dietary protein intake and the role of
conditionally essential amino acids in muscle and bone-healing after a
Methods: One hundred adult male rats were used. Ten rats served as
controls and received a 15% protein diet throughout the study. The remaining
ninety rats received a 6% protein diet for five weeks to induce protein
malnutrition. The rats underwent intramedullary nailing and closed midshaft
fracture of one femur. After the fracture, they were separated into three
isocaloric dietary groups. Group P6 received a diet with 6% protein; Group
P15, a diet with 15% protein; and group P30, a diet with 30% protein with
conditionally essential amino acids. At two, four, and six weeks after
surgery, ten animals from each group were killed and the femora were evaluated
with dual x-ray absorptiometry, histomorphometric assessment of callus, and
torsional testing. The quadriceps muscles were analyzed for total mass, total
protein content, and for mRNA expression of insulin-like growth factor-1
(IGF-1), IGF-2, IGF receptors, actin, myosin, and vascular endothelial growth
Results: The P30 group demonstrated elevations in albumin, body
mass, muscle mass, total protein content of muscle, and bone mineral density
in the fracture callus compared with the P6 diet group at six weeks (p <
0.05). Molecular analysis of muscle revealed that IGF-1, IGF-2, IGF receptors,
myosin, actin, and VEGF gene expression were significantly (p < 0.001)
higher in the P6 group compared with the P30 group. Biomechanical testing of
the femora, however, showed no significant differences.
Conclusions: Dietary supplementation with conditionally essential
amino acids in malnourished animals had anabolic effects on bone
mineralization, body mass, and muscle mass.
Clinical Relevance: Identifying methods for augmenting skeletal
muscle and fracture-healing by means of oral protein supplementation may
provide cost-effective, direct clinical benefits to orthopaedic patients.