- The satiety chemicals led by CART (the C stands for cocaine and A for amphetamine, since these drugs put this chemical into overdrive). CART stimulates the surrounding hypothalamus to increase metabolism, reduce appetite, and increase insulin to deliver energy to cells rather than be stored as fat.
- The eating chemicals driven by NPY (a protein called neuropeptide Y). NPY has the opposite effect on the hypothalamus—decreasing metabolism and increasing appetite. It fires off those signals for you to eat, eat, eat. The biological message: Prevent starvation by eating.
Think of the two substances—NPY and CART—as villain and angel. Both are competing for the same parking space, the one that will ultimately determine whether or not you eat. They both arrive at the same time and want that space. Either more NPY or CART sneak into the place, thus sending the all-important go or stop signal to your brain to influence the hormones that make you feel full or hungry.
How do we know these centers work this way? In animal models, we see that if a rat's eating center is destroyed, it forgets to eat and starves. In rats where the eating center is over-stimulated, though, they eat themselves to death—literally—by increasing their fat-induced diseases like diabetes, hypertension, and arthritis.
In a perfect system, your offense and defense complement each other; you get the foods you need and stop when you've had enough. Unfortunately for everyone except elastic-waistband manufacturers, a lot of things can mess up those systems.
Find out more about this book:YOU: On A Diet Revised Edition: The Owner's Manual for Waist Management