How does your brain react to a change in body weight?
Your brain fights to keep your body at a predetermined weight (often called the set point) in order to maintain the optimal amount of fat storage. The specific area in the brain that automatically regulates this in your body is called the hypothalamus.
The hypothalamus uses a complex bio chemical process to regulate appetite and food intake. This means that when you go above or below your set point, your brain will push your body to settle back into what it believes is your ideal weight.
Unfortunately, when a person is over weight or obese this process naturally stores significantly more fat than it should.