Bone Abstracts

This study aims at determining if casein would lead to a better bone status than soy in the context of a moderate protein restriction (6% of total energy intake) in growing mice.

Ten-week-old female Balb/C mice were divided in four groups of 15 animals. Two groups received 6% of their energy intake as protein, one as casein and the other as soy protein. The third group was a normal-protein control receiving 20% soy protein. The last group (positive control) was fed the 6% soy protein diet and had a daily injection of PTH 1–34 used as an anabolic agent. After 8 weeks, all animals were sacrificed, blood parameters were measured and L2 vertebrae and femur were analysed by micro-tomography.

The 6% soy mice were smaller and lighter than their casein counterparts because or reduced lean tissue gain. In the femur, the 6% casein and 20% soy diets led to a better bone status than the 6% soy diet as evidenced by higher cortical thickness, bone volume (BV/TV) and trabecular number. The 6% soy mice also had a higher femoral structure model index (SMI), i.e. more plate-like structure conferring more mechanical resistance. Serum analysis showed higher levels of P1NP, IGF1 and CTx in the 6% casein and 20% soy groups than in the 6% soy group. Uterus and spleen weight were smaller in the 6% soy group. PTH daily injection had a beneficial effect on P1NP and on femoral parameters when compared with the 6% soy group and a beneficial effect on vertebrae parameters against all other groups.

This study demonstrates that during moderate protein restriction, casein maintains better bone status than soy. The mechanism involved is not known but may partly involve the reduced amount of methionine, proline or leucine found in soy protein as compared to casein.