You: On a Diet: The Insider’s Guide to Easy and Permanent Weight Loss. Michael Roizen F.

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 stress. This may be why some people in chronically stressful situations tend to gain weight. Testosterone, the male sex hormone, seems to stimulate NPY secretion, while the female sex hormone, estrogen, seems to have a varying effect depending on the stage of a woman’s cycle.

      But our bodies aren’t always perfect, and leptin doesn’t always work the way it’s supposed to. In some research, when leptin was given to mice, their appetites decreased, as expected. When it was given to people, they initially got thin, but then something strange happened: They overcame the surge of leptin and stopped losing weight. This indicates that our bodies have the ability to override leptin’s message that our tank is full. How? When leptin tells your defense—the satiety chemicals—to kick in and protect you against stray bonbons, the pleasure center in your brain says, “Uh, yeah, three more this-a-way” That surge from the pleasure center, which we’ll discuss in more detail in part 3, can overrule leptin’s messages that you’re full. That’s called leptin resistance (there’s another form of leptin resistance as well, which happens when cells stop accepting leptin’s messages). Most obese people, by the way, have high leptin levels; it’s just that their bodies have the second form of leptin resistance—they don’t receive and respond to leptin signals.

      That doesn’t mean leptin is always on the losing end of this chemical battle. YOU-reka! The challenge is to let leptin do its job so that the brain demands less food. One way to do it: Walk thirty minutes a day and build a little muscle (that’s part of our activity plan in part 4). When you lose some weight, your cells become more sensitive and responsive to leptin.

      FACTOID

      Scientists found how ghrelin works accidentally: in gastric bypass surgery, doctors cut out the part of the stomach that secretes ghrelin. They soon realized that it wasn’t just the smaller stomach but the reduced ghrelin production that helped surgery patients eat less food. The eat-everything signal was shut off, clearing the way for the satiety center to take care of its business.

      Ghrelin Is the Gremlin: The Hormone of Hunger

      Your stomach and intestines do more than hold food and produce Richter-worthy belches. When your stomach’s empty, they release a feisty little chemical called ghrelin. When your stomach’s growling, it’s this gremlin of a hormone that’s controlling your body’s offense; it sends desperate messages that you need more points, you need to score, you need to FedEx the chili dogs to the GI tract immediately. Ghrelin makes you want to eat—by stimulating NPY. YOU-reka! To make things worse, when you diet through deprivation, the increased ghrelin secretion sends even more signals to eat, overriding your willpower and causing chemical reactions that give you little choice but to line your tongue with bits of beef jerky.

      Ghrelin also promotes eating by increasing the secretion of growth hormone (ghre is the Indo-European root word for “growth”). So when you increase ghrelin levels, you stimulate that growth hormone to kick in, and growth hormone builds you not only up but out as well.

      Your stomach secretes ghrelin in pulses every half hour, sending subtle chemical impulses to your brain—almost like subliminal biological messages (carrot cake, carrot cake, carrot cake). When you’re really hungry or dieting, those messages come fast—every twenty minutes or so—and they’re also amplified. So you get more signals and stronger signals that your body wants food. After long periods, your body can’t ignore those messages. That’s why sugar cookies usually trump willpower, and that’s why deprivation dieting can never work: YOU-reka! It’s impossible to fight the biology of your body. The chemical vicious cycle stops when you eat; when your stomach fills is when you reduce your ghrelin levels, thus reducing your appetite. So if you think your job is to resist biology, you’re going to lose that battle time after time. But if you can re-program your body so that you keep those ghrelin gremlins from making too much noise, then you’ve got a chance to keep your tank feeling like it’s always topped off.

      Food Fight: The Ghrelin Versus Leptin Grudge Match

      So now let’s get back to that offense and defense. The natural state is for you to have a give-and-take relationship between your eating and satiety chemicals—between your ghrelin and leptin levels—to influence NPY and CART, respectively. It’s the relationship between the impulse that says, “I’ll take a large pepperoni with extra cheese,” and the one that says, “No more passengers, this belly is full.”

      This battle over eating isn’t between your willpower and the Belgian waffles; it’s between your brain chemicals. The NPY is the villain—encouraging you to buffets, driving you to the pantry, pointing its chemical finger to the convenience foods, while CART is your dietary guardian angel, which encourages a cascade of allies to keep