New Clues to How the Brain and Body Communicate to Regulate Weight

Assuming there are communications.

Maintaining a healthy body weight may be difficult for many people, but it's reassuring to know that our brains and bodies are wired to work together to do just that -- in essence, to achieve a phenomenon known as energy balance, a tight matching between the number of calories consumed versus those expended. This careful balance results from a complex interchange of neurobiological crosstalk within regions of the brain's hypothalamus, and when this "conversation" goes awry, obesity or anorexia can result.

The answer to "how" is "poorly" in the fat (because of bad brain) and "just fine" in the intended-sized.