New research shows that people who have a low level of a certain hormone may be much more likely to be overweight than those whose level is normal. The hormone is called MSH--short for melanocyte-stimulating hormone--and has been tested so far only in mice. Specifically, the level of MSH regulates how fat is partitioned between storage and metabolism. At low levels of MSH, storage is favored over metabolism, while at high levels metabolism is favored over storage. This is the natural way that the body integrates appetite in the brain and metabolism in the body."