regular, monogamous, healthy sex. When the appetite function for sex was satisfied, the appetite function for food was diverted.)
FACTOID
As you get older, you have fewer leptin receptors in your hypothalamus-meaning that you have fewer satiety signals, which makes you more prone to gaining weight.
Hidden in your hypothalamus, you have a satiety center that regulates your appetite. It is controlled by two counterbalancing chemicals that are located side by side (see Figure 2.2).
The satiety chemicals led by CART (the C stands for cocaine and the 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 muscle 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; it decreases metabolism and increases appetite.
Think of these two command chemicals as any game or sport that involves offense and defense, like soccer, checkers, or even dating. The offense is always trying to make advances, trying to score points, and trying to attack, while the defense protects its territory.
Your eating chemicals play offense. They want as many points as possible, so they fire off those signals for your body to score: eat, eat, eat, calories, calories, calories, chimichanga, chimichanga, chimichanga. The biological message: Prevent starvation by eating. Meanwhile, your satiety chemicals play defense, like a goalkeeper, the back row of checkers, or a protective parent. They send the messages to your brain that you’re full, to shield you from steadily pumping bacon-wrapped scallops down your gullet. How do we know these centers work this way? For one, by looking at extremes and seeing what happens when the feeding system is turned completely on or off. When we study animal models, we see that if a rat’s eating center is destroyed, for instance, it forever forgets to eat. The resulting severe anorexia starves the body of all energy and nutrients so that it withers away to the approximate width of an envelope. In rats whose eating center is overstimulated, though, food is always on the radar screen. And those rats eat themselves to death—literally—by increasing their fat-induced diseases like diabetes, hypertension, and arthritis.
Figure 2.1 Food Fight In your hypothalamus, you have hunger and satiety chemicals. The hormone leptin goes to the satiety center to make you feel full and satisfied, while the signal from the hormone ghrelin makes you want to eat gorge, and slobber over your every feast.
Figure 2.2 Chemical Reaction If we look closely at the hypothalamus, we see that a small nucleus at the bottom houses NPY and CART, which fight the yin-yang battle to control the brain biochemistry of hunger. Each chemical readily travels to other nuclei in the hypothalamus. NPY causes our temperature to drop and our metabolism to decrease as we feel hungry. CART stimulates the opposite influence. The nearby mammillary body (literally shaped like a nipple) is part of our limbic system, where we store memories and emotions—just the right combination to create a craving for a favorite food. The thalamus is the body’s relay station and rapidly transmits orders throughout the brain based on the desires of the eating center.
FACTOID
CART (cocaine-amphetamine-regulatory transcript for those scoring at home) is the reason why cocaine addicts don’t gain weight. Cocaine and amphetamine stimulate this chemical, giving you a double brain bat to help you control appetite and increase metabolism. It’s unclear whether CART will be the basis for effective weight-loss treatments, but researchers are studying the neurological effects these drugs have on appetite to see if they could lead to long-term pharmaceutical solutions to weight loss (without of course, the dangerous side effects of illicit drugs). Marijuana, by the way, has its own receptors that overwhelm leptin, which is one big reason why pot smokers get the munchies. It’s also an area that’s a promising new approach to weight-loss drugs. By figuring out how the drug turns off the gene that produces leptin, we’ll be able to figure out how to flick it on-to keep leptin (and thus satiety levels) high. The prototype drug has done great in trials and symbolizes a new generation of smart weight-loss medications that work hormonally.
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 (many of which we’ll discuss in a moment). But these obstacles aren’t insurmountable. You can take comfort (and find motivation) in the fact that your body wants you to reach your goals. Your body doesn’t want to be bigger than it should be. Your body doesn’t want lots of excess fat. Take the case of rats made obese by force-feeding. When they’re allowed to eat freely, they go back to their control weight. They eat what they should eat, without thinking. Same goes for starving rats. When allowed to eat again, they don’t gorge. They naturally go back to their control weight. And we know from years and years of research that what rats do is a pretty fair indication of what humans will do under the same circumstances. (Humans, of course, will do what rats do when they’re motivated only by biology. A rat isn’t upset by stress at home or work, which is why controlling the emotional aspect of eating plays such a big role in effective waist management, as we’ll discuss in Part 3.)
YOU-reka! If you can allow your body and brain to subconsciously do the work of controlling your eating, you’ll naturally gravitate toward your ideal playing weight. You do it by developing a well-trained defense that naturally balances the offense. When you do, you’ll win the diet game every time, whether you have willpower or not. Though it may not always be the case in football or Scrabble, when you pit offense against defense in your body, the offense in your body typically attacks more aggressively. It’s simply easier to scoop up bean dip than it is to leave it for others.
The Hunger On and Off Switches
Duct tape over your mouth isn’t how your body regulates food intake. Your body does it naturally through the communication of substances controlled by your brain. Although there are many hunger- and obesity-related hormones waiting to be discovered, there’s enough evidence to suggest that two hormones have as much influence for dictating our hunger and satiety levels as a head coach does on offense and defense—hour to hour and year to year.
Lovin’ Leptin: The Hormone of Satisfaction
In sumo champions, a little extra fat can produce good results. But we also think that fat has an unfair knock against it. Fat is treated a little like an accused suspect; it sometimes gets a bum rap. Fat produces a chemical signal in your blood that tells you to stop eating. Left to its own devices, fat is self-regulating; the problem occurs when we override our internal monitoring system and continue to stuff ourselves long after we’re no longer hungry. Your body knows when it’s had enough, and it prevents you from wanting any more food on top of that. How does fat curb appetite? Through one of the most important chemicals in the weight-reduction process: leptin, a protein secreted by stored fat. In fact, if leptin is working the way it should, it gives you a double whammy in the fight against fat. The stimulation of leptin (the word comes from the Greek word for “thin”) shuts off your hunger and stimulates you to burn more calories—by stimulating CART.
FACTOID
Neuropeptide Y is a stress hormone that increases with severe or prolonged
