Dietary Protein Supplementation Increases Peak Bone Mass Acquisition in Energy-Restricted Growing Rats

Abstract

Peak bone mass is a major determinant of osteoporosis pathogenesis during aging. Respective influences of energy and protein supplies on skeletal growth remains unclear. We investigated the effect of a 5-mo dietary restriction on bone status in young rats randomized into six groups (n ϭ 10 per group). Control animals were fed a diet containing a normal (13%) (C-NP) or a high-protein content (26%) (C-HP). The other groups received a 40% protein energy-restricted diet (PER-NP and PER-HP) or a 40% energyrestricted diet (ER-NP and ER-HP). High-protein intake did not modulate bone acquisition, although a metabolic acidosis was induced and calcium retention impaired. PER and ER diets were associated with a decrease in femoral bone mineral density. The compensation for protein intake in energy-restricted conditions induced a bone sparing effect. Plasma osteocalcin (OC) and urinary deoxypyridinoline (DPD) assays revealed a decreased OC/DPD ratio in restricted rats compared with C animals, which was far more reduced in PER than in ER groups. Circulating IGF-1 levels were lowered by dietary restrictions. In conclusion, both energy and protein deficiencies may contribute to impairment in peak bone mass acquisition, which may affect skeleton strength and potentially render individuals more susceptible to osteoporosis. In particular, alterations in energy intake have been demonstrated to impair bone quality and strength in rodent models (1-5). Lamothe et al. (1) and Mardon et al. (2) reported that energy restriction adversely affected bone mineral content (BMC), bone mineral density (BMD), and mechanical properties in old rats, despite a micronutrient compensation. Nevertheless, the impact of energy restriction on bone was suggested to be modulated by the age at onset of restriction (5,6). To date, no clear consensus regarding the effects of energy restriction on peak bone mass acquisition has been established.Protein intake is widely linked to bone growth, hence to bone strength (7). Indeed, collagen is the major constituent of bone organic matrix, and noncollagenic proteins are involved in the regulation of the mineralization process. Dietary proteins provide the essential amino acids necessary for new matrix synthesis and may modulate circulating IGF-1 levels as well, an osteotrophic growth factor (8). In growing animals, protein deficiency was demonstrated to lead to decreased bone status (9). Ammann et al. (10) also reported that a 2.5% casein diet during 16 wk in 5-mo-old rats was associated with bone loss.Consequently, one would expect high-protein intake to promote bone health. However, other reports suggest that such a diet may alter calcium homeostasis in ways that could lead to bone loss (11,12). The metabolic acidosis, derived from sulfur amino acids catabolism, would also exert a direct stimulatory effect on bone resorption and an inhibitory action on matrix mineralization (13,14). Actually, the role of dietary protein on bone remains controversial.In the current context of rising incidence of obesity...

The Interaction of Voluntary Running Exercise and Food Restriction Induces Low Bone Strength and Low Bone Mineral Density in Young Female Rats

“…This difference might have been caused by the difference in the age of the rats. The age of the rat in the exercise and food restriction phase was lower in our study (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) weeks old) than in Dimarco et al's study (17-30 weeks old). Our findings could suggest that young female rats may be sensitive to the negative effects of the interaction of voluntary running exercise and food restriction.…”

“…Previous studies have reported that food restriction in sedentary female rats induces low BMD [12][13][14]. Furthermore, it has been reported that food restriction in female rats undergoing an exercise regimen induced low bone mineral content (BMC) [9,10] and BMD [11].…”

The effects of dietary protein and amino acids on skeletal metabolism

“…Ten-week-old growing rats were fed an energy restricted diet or diet in which both protein and energy were restricted. When casein was supplemented to either one of these diets such that the percent of energy from protein equaled or exceeded that in a normal diet the animals demonstrated a significant protective effect against bone loss (Table 1, Mardon et al, 2009). BMD was lowest in animals that were placed on the energy and protein restricted diets compared to animals whose diets were solely calorically restricted.…”

Long-term supplementation with young coconut juice does not prevent bone loss but rather alleviates body weight gain in ovariectomized rats

“…The data are presented as the mean ± standard error of the mean, and data management and statistical analyses were performed with JMP 9.0.2 (SAS Institute Inc., Cary, NC, USA). The specific effects of Ovx and YCJ supplementation were examined by comparing values of the Sham, Ovx and Ovx+YCJ groups using analysis of variance and analysis of covariance with body weight as the covariate (26,27), with Tukey's honest significant difference (HSD) test. P<0.05 was considered to indicate a statistically significant difference.…”