Research in animal models has demonstrated the role of osteocalcin, a bone formation marker, in regulation of energy metabolism. Those studies have led to a new concept of the bone acting as an endocrine organ by secreting osteocalcin, which acts by increasing insulin secretion, lowering plasma glucose, and increasing insulin sensitivity and energy expenditure. Results in humans have been conflicting. On the other hand, antiresorptive drugs used against osteoporosis decrease osteocalcin levels, while anabolic drugs increase osteocalcin levels. However, the effects of these therapies on energy metabolism have not been investigated.