ANALYSIS OF THE IMPACT OF A DIETARY LOW BIOLOGICAL VALUE PROTEIN ON BONE BIOMECHANICS OF GROWING RAT

Keywords: bone biomechanics, gluten, protein malnutrition          
OBJETIVES: This investigation was undertaken to analyze the impact of feeding a protein with a low caloric value, which is profusely used in human nutrition, on the indicators of biomechanical quality of the rat femoral diaphyseal cortical bone. METHODS: Female Sprague-Dawley rats aged 30 d (n = 60) were fed ad lib diets containing 5, 10, 15, 20, 25 or 30 % wheat gluten (G) (BV = 24.2) between 30 and 90 d of life. Rats fed a 20% casein (C) (BV = 100) were taken as controls. Body growth was evaluated in terms of variations in body weight, whereas longitudinal skeletal growth was done in terms of both body and tail lengths. The parameters were measured weekly. Growth as function of accumulated food intake and its conversion in biomass was evaluated by applying the Parks’ equation. Rats were sacrificed at the end of the experimental period. The right femur was cleaned and biomechanically tested to failure by three-point bending in an Instron 4442 test machine that was operated in stroke control at a constant rate of 5mm/min. The graphic analysis of the load/deformation curves obtained permitted the estimation of the biomechanical quality of the tested bones. Results were expressed as X±SD and statistically evaluated by ANOVA and Tukey-Kramer test. RESULTS: The groups below 15% G were unable to support growth that was only minimal in the remaining ones. An increasing efficiency of conversion of food into biomass with increasing concentration of G in the diets was apparent, although it was significantly lower than in C rats. Bone mass was significantly and negatively affected in response to G and did not reach normality even at the highest G concentration. This negative effect was also seen in the extrinsic biomechanical properties of the bone. The intrinsic stiffness (material property) was not affected by treatment. CONCLUSION: Diets containing wheat gluten as protein source induce a deficit of growth at the level of the biomass, which is accompanied by a negative effect on the biomechanical behavior of the mid-diaphyseal femoral shaft. This could be the expression of the subnormal bone size in response to the impaired rate of the skeletal growth. The material quality of cortical bone tissue was not affected by treatment. Supported by UBACYT O-002 and O- 005.