The human body is amazing. We are highly adaptive creatures and our bodies work to create equilibrium. When you are dieting and eating 1200 calories a day, your body will adapt and figure out how to live off of 1200 calories.
The host - Stephenie Meyer. Melanie Stryder refuses to fade away. Earth has been invaded by a species that takes over the minds of human hosts while leaving their bodies intact, and most of humanity has succumbed.