Long-term consumption of high-
protein (HP) diets at 35% of energy is postulated to negatively influence bone health. Previous studies have not comprehensively examined the biochemical, physical, and biomechanical properties of bone required to arrive at this conclusion. Our objective in this study was to examine the long-term effect of a HP diet on bone metabolism, mass, and strength in rats. Adult female Sprague-Dawley rats (n = 80) were randomized to receive for 4, 8, 12, or 17 mo a normal-
protein (NP) control diet (15% of energy) or a HP diet (35% of energy). Diets were balanced for
calcium because the
protein sources were rich in
calcium. At each time point, measurements included
weight, body composition, and bone mass using dual-energy X-ray absorptiometry, mechanical strength at the mid-diaphysis of femur and tibia, microarchitecture of femurs using microcomputerized tomography and serum
osteocalcin, carboxy-terminal crosslinks of
type I collagen (CTX),
insulin-like growth factor-1 (IGF-1),
leptin, and
adiponectin. Effects of diet, time, and their interaction were tested using factorial ANOVA. The HP diet resulted in lower
body weight, total body, and abdominal fat and higher lean mass. Serum
leptin and
adiponectin were greater in HP-fed than in NP-fed rats, but
IGF-1 did not differ between the groups. Whereas the HP diet resulted in higher relative bone mineral content (g/kg) in the femur, tibia, and vertebrae, serum
osteocalcin and CTX and bone internal architecture and biomechanical strength were unaffected. In conclusion, HP diets at 35% of energy lower body fat content without hindering the mechanical and weight-bearing properties of bone.