Health At Every Size: The Surprising Truth About Your Weight by Linda Bacon Read Free Book Online Page B

leptin, even more than their thinner counterparts. The amazing results seen in the ob/ob mice only worked in the few humans with a similar genetic mutation . 20 Less than a dozen people have since been discovered to have this mutation.
     
    The difficulty for many humans lies in the decreased sensitivity of the brain to leptin’s effects. In other words, your fat meter is working fine: Your fat cells send leptin to the brain to initiate the steps to turn off your appetite and speed up your energy use, but it’s as if the part of your brain that receives the message is swathed in cotton batting—it can’t “hear” the message very well. Thus, your brain doesn’t do its part by triggering the cascade of effects to reduce appetite, increase physical activity, and supercharge metabolism.
     
    Leptin’s main role appears to be protecting against weight loss in times of scarcity. When your fat stores shrink when you’re dieting, so does leptin production. In response, your appetite increases and your metabolism decreases and you gain the weight back.
     
    The opposite, however, is not as strong. Beyond a certain point, increased weight and the resulting increased leptin production do little to blunt appetite or increase metabolism because you hit a limit in your ability to sense the leptin. In other words, your brain is relatively less concerned with preventing weight gain in times of plenty.
     
    This point is very important to understand, so let me explain it in others terms. Weight gain is relatively easy, but the human body is just not designed to support weight loss. This means that reversing weight gain habits will do a pretty good job of preventing weight gain, though they may not result in weight loss.
     
    Another fact frustrating to many is that people with a history of repeat dieting send out less leptin than they would without that history. 21 22 This decrease is one of the mechanisms that explains why many chronic dieters tend to be heavier than those who haven’t attempted weight loss. Your body has reset your setpoint to a higher level. Lucky you—you now have an extra layer of protection so you won’t wither away next time you go on a diet (which the body perceives no differently than a famine). Very effective if you lived in another era, but perhaps not so appreciated amidst today’s plenty.
     

Beyond Leptin
     
    Though it isn’t the magic weight-loss panacea it was initially envisioned to be, the discovery of leptin was a big advance in understanding weight regulation. We learned that it has an extremely powerful effect on our weight and is the cornerstone of our setpoint mechanism, even if we aren’t sure how to harness this power.
     
    The thousands of studies on leptin also spawned even greater research on the neurocircuitry underlying metabolism and on other hormones and neurotransmitters that support leptin. For example, we discovered that insulin, best known for its role in regulating your blood sugar (more on that in chapter 4), is an important ally, informing your hypothalamus about the amount of energy circulating in your bloodstream from your recent meals. Insulin’s message gets amplified by several other gut hormones and nerves that respond to the volume and type of food you eat and other chemical messengers that are sensitive to sensations such as the stretch of your stomach or the texture or temperature of the food you eat.
     
    In 1999, researchers discovered another particularly powerful hormone, ghrelin, that contributes to strong feelings of hunger. All day, ghrelin concentrations rise and fall in our bodies. Although we’re not aware of these ups and downs, they help drive our behavior on a deeply subconscious level, either moving us toward the table or away from the plate. In recent years, research has also begun pointing to the various diet and lifestyle factors that modify the body’s production of ghrelin and other eating-related signals.
     
    Although many scientists