Gerard Karsenty, now at Columbia (with various cohorts, the most common being Patricia Ducy, his now-wife) has spent some 15 years investigating the interactions and regulations effected by osteocalcin (controls the processes by which calcium phosphate is deposited onto bone cells). In a fairly radical theory (even to this day) Karsenty has been studying the links between osteocalcin (which affects the skeletal system (bone) and energy metabolism. Energy metabolism is a process that goes askew in diabetes. (Our bones are involved with dynamic processes: Osteoblasts form and shape bone tissue, while osteoclasts break it down; the system is called “remodeling”.)
Karsenty also found that leptin (which suppresses appetite) blocks bone growth, even though there is no direct signal from leptin to the bone cells. Moreover, once leptin is infused into mouse brains, bone growth returns to normal). It seems that leptin inhibits the synthesis of serotonin (in the brain, where most homeostatic processes¹ are regulated), which then attenuates bone growth. But, since homeostatic processes are part of feedback loops, there must be a mechanism by which bone growth affects energy metabolism. It turns out that osteocalcin deficiency is related to insulin-resistant, glucose intolerance (diabetes).
Karsenty determined that eating promotes the release of insulin, which then activates bone remodeling. Osteoblasts produce osteocalcin when forming bone; bone resorption activates the hormone (releases it into the blood stream) which then notifies the β-cells (in the pancreas) to boost insulin production (and glucose uptake). [These two articles referenced above have a great graphical depiction.] This regulatory mechanism operates on a longer-term basis than the normal insulin response.
These mice studies seem to have the most relevance to overweight humans, where insulin resistance and low bone turnover is common.
¹Homeostasis refers to the ability to regulate an organisms interior milieu, ensuring stability due to fluctuations in the environmental surrounding it.