Serum osteocalcin concentrations in protein and/or energy restricted rats

The effects of protein and/or energy deficiency on serum osteocalcin concentrations were studied in growing rats. Animals were fed a high or a low protein diet (respectively 22 and 6% casein) either ad libitum or restricted (60%). After four weeks, serum osteocalcin concentrations were significantly decreased by imposed energy restriction. However, they were not affected by protein deficiency, although growth was similarly reduced in both cases. By comparison, serum transthyretin concentrations were decreased by protein and/or energy deficiency, and they were significantly correlated with serum osteocalcin concentrations. These results suggest that serum osteocalcin concentrations are not a reflection of bone growth in protein and energy restricted rats, but are related to energy availability.