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1 year ago
How to Stop Cravings

With all the energy we devote to the epic struggle to control our weight, we know remarkably little about the most obvious reason diets fail: We get hungry. What's going on when our bodies tell us, insistently, that we have to eat that double bacon cheeseburger right now — even though we've got plenty of fat stores to pull from? Why can some people go without eating for hours while others freak out if they miss their 4 p.m. cookie? And exactly what are those nasty growling noises?

The good news: Researchers are hard at work investigating this most basic of human impulses. The bad: That task is proving to be surprisingly difficult. Just when scientists think they've uncovered the key to appetite, a new hormone or biological process or brain function emerges. But what we do know is still pretty fascinating. We'll bring you up to date on the latest science regarding how hunger develops in our bodies — and the breakthrough news on what might make those pangs a little easier to control.

The Body Clock

You've been revising that presentation all morning, your mind is on your work and your deadline — until your stomach gurgles and suddenly you find yourself thinking about ham and cheese. Or beef with broccoli. Or Twizzlers. Or that half-eaten granola bar in the back of your desk. You're hungry. Again. But how? Why?

The why part makes perfect evolutionary sense. For most of human history, food was in short supply, and if you didn't eat when you could, there was a very good chance that you might not eat at all. If you didn't eat, you didn't survive, which inevitably had a way of lowering the odds that you'd reproduce. Bad survival strategy. It's important to note here that that drive to eat as much as we could, whenever we could, was spawned long before there were Snickers, Krispy Kremes, or Quarter Pounders with Cheese. And even as we evolved into a world of drive-through eateries and 24-hour mini-marts, our basic bodily urges remained in the prehistoric era. Now that hunting and gathering has a whole lot more to do with sample sales than procreation, that drive to survive takes us straight to the vending machine every afternoon at 3 o'clock. It's easy to eat because we have to. And it's hard to stop because, technically, we're not supposed to — which makes for one helluva genetic deck stacked against us.

If we understand just how the genetic deck is stacked, we can get a better grip on handling our hunger. Science has nailed the basics. That prelunch gurgling? "That's just air bubbles moving around in your stomach and upper intestines as they begin to undergo muscle contractions in anticipation of a meal," says David E. Cummings, M.D., of the University of Washington. Ick, but good to know. [The bigger question is how your brain creates that sensation of hunger in the first place.] Hormones play a major role, and new research is zeroing in on one in particular.

Hungry Hormones

It's called ghrelin. It sounds like something your kid should be for Halloween, but it's a hormone secreted by your stomach and, to a lesser extent, your intestines. Research linking ghrelin to hunger began just a few years ago, and therefore our knowledge is far from complete. But scientists believe the hormone, which rises when you haven't eaten in a while and falls after you nosh, may be one of the main drivers of that gnawing, gimme-a-cookie feeling. "When we put people in a room with no external cues and measure their ghrelin, the subjects say they want to eat when ghrelin peaks," Dr. Cummings says.

A group of scientists at London's Imperial College took the correlation one step further. They gave a group of 12 lean subjects and 12 overweight subjects low-dose ghrelin injections. They found the shots increased food intake 20 percent in the lean group and a whopping 70 percent in the overweight group. Unfortunately people who most need to lose weight are often those who have the largest appetites, in part because excessive weight, for reasons still unknown, seems to reduce the body's ability to regulate its hunger hormones.

We do know that, no matter how much you weigh, when your ghrelin level rises, you get hungry. Two of the main factors that control ghrelin levels are what you eat and when you eat. But both a lack of sleep and significant weight loss can also elevate ghrelin levels. And here's some encouraging news for those of you struggling to adapt to a new diet: Within a few days, your ghrelin level (unlike your boss or your boyfriend) adjusts to your schedule. For example when you decide you're going to move your noon lunch to 2 p.m., ghrelin is part of what makes that first day a doozy; you'll be ravenous at your usual lunchtime. By the second day, it's a bit better. By the third day, your ghrelin levels should adjust — and you'll be walking past the cafeteria with barely a gurgle.

Habits aren't everything, though. Ghrelin responds differently to different kinds of food. "Carbs have the deepest and best suppression of ghrelin, and protein is almost as good — longer, but not quite as deep," Dr. Cummings says. Although researchers are still discovering why certain foods trigger ghrelin more than others, they do know which foods are more likely to cause a spike. "Fats are substantially less good" at keeping levels low, Dr. Cummings says, "which may be one of the reasons high-fat diets promote weight gain."

The Stomach Saga

Meanwhile, back at your desk: Ghrelin spikes and you're hungry. You put down the presentation, put on your coat, and head to the deli for that ham and cheese (on whole wheat with lettuce and tomato). You take the first bite and digestion begins.

When that ham and cheese reaches your stomach, your body begins to absorb the nutrients, and your ghrelin levels start to go down. Once that sandwich hits your intestines about 15 to 20 minutes later other hormones join the party. "There are six or eight satiety hormones released by your gut," Dr. Cummings explains. Those hormones relay the "getting full" message to your hindbrain, which passes it on to other parts of the brain, and you start to feel satisfied.

While all that's happening, there's another, more basic "getting full" message building up: gastric stretch. When you load up your stomach with food it physically stretches, telling your brain to ease up on the eating. Together, these messages say enough. At which point if you're listening, you pick up the rest of that sandwich and wrap it up or toss it out.

When you lose weight, your ghrelin levels fight you by going up. "We found measurable ghrelin increases in people who lost as little as 1.5 percent of their weight," Dr. Cummings says. Translation: The more you lose, the more your body wants you to eat. So while you're aiming to rock a teeny bikini by June, your body wants to make sure you can survive a winter without food. Very useful in primitive times. Now? Not so much.

Find a way to regulate ghrelin, Dr. Cummings speculates, and you might find a way to curb hunger and help keep the pounds off. But others say hitching hunger to one hormone is too simple. "Hormonal regulation of appetite is an extremely complex area," says Arline Salbe, Ph.D., R.D., a research nutritionist with the National Institutes of Health.?"It's the interplay of several hormones, along with other yet unknown molecules, that is probably most important."

One of those other hormones is leptin. A few years ago, it was the go-to hormone in hunger research. While ghrelin triggers the desire to eat, leptin, which is generated by fat cells, triggers the desire to stop eating. When people lose weight, their leptin levels drop — and they get hungrier, which explains why most people who lose weight eventually gain it back. Columbia University scientists recently completed a study in which they injected leptin into people who had recently lost weight, restoring the hormone's levels to where they were before weight loss. The results were promising: The additional leptin reversed changes in the dieters' bodies that normally make it hard to keep weight off (including a slower metabolism, lower adrenaline levels, and less calorie burning for the same amount of exercise).

While research on leptin continues, the many scientists who initially touted it as the secret to stopping hunger began to think that ghrelin was actually the most important piece of the appetite puzzle. That was before the detection of a brand- new hunger hormone: obestatin. Identified just last year by Stanford researchers, obestatin apparently contributes to satiety by slowing the speed at which food travels through your digestive system. In the Stanford study, mice who got obestatin injections cut their food intake in half. Whether it will work in humans is the multibillion-dollar question for Johnson & Johnson, the drug company that funded the research. The scientific community is still seeking to identify just how ghrelin, obestatin, and leptin work in the body, so it could be years before any potential drug therapy based on these hormones hits the market. Can't wait that long? Several hunger-curbing drugs are already on the market — but they're definitely not for everyone (see "appetite for prescription").

The Stress Factor

There's more to appetite than the steady ebb and flow of hunger hormones. A tough day always makes it harder to walk by the brownies your colleague has so thoughtfully brought to the office, even when your body isn't really hungry. The same urge to snack when stressed happens to rats, says Mary Dallman, Ph.D., a physiology professor at the University of California at San Francisco. "If you put rats in a stressful situation, they go for sweets and fats at the expense of their normal rat chow," Dr. Dallman says. In other words, stress not only makes them eat more, but it sends them right to high-calorie, bad-for-them stuff.

It turns out that both humans and rodents have similar primal brains where the control centers for both hunger hormones and the stress hormone cortisol live. When your body is low on energy or is undergoing stress, cortisol is released to help raise blood sugar. When you're stressed having increased blood sugar is an asset — it gives you energy to fight or flee. But increasing blood sugar also increases your appetite, and that sends you chasing after that brownie.

Constant Cravings

But this still doesn't explain why you're rooting through the fridge an hour after a leisurely Sunday brunch. In this case a craving for afternoon sugar is probably just that — a craving. Unlike hunger, which comes from a deeper, more primitive section of the brain, the cravings department is located right in the middle of the "want" section of your brain. It's all about pleasure — and the simple fact that you're programmed to want more of it.

Your craving for that deep-dish double-cheese slice is actually a conditioned habit, coming from factors that are cultural and psychological, not physiological. Maybe it's the Snickers bar you consume to fight the mid-afternoon sleepies, or the cookies after dinner, or the chips you like to eat during your favorite TV show. Pretty soon you're like one of Pavlov's dogs. You hear the bell — or the opening chords of the Will?&?Grace theme song — and you salivate.

When you experience a craving, it triggers the areas of the brain — the hippocampus, insula, and caudate — that also cause addictions. The same mechanism that makes you (well, not you) reach for a crack pipe makes you yearn for the New York Super Fudge Chunk. "Whether it's a craving for drugs, or chocolate, or shoes," says Marcia Pelchat, Ph.D., who studies food cravings at the Monell Chemical Senses Center in Philadelphia, "the mechanism in the brain is the same."

Despite what we all desperately want to believe, a craving isn't your body's way of saying you need a sugar boost. The only craving that seems to be physiologically based is salt, Dr. Pelchat says, and that's exceedingly rare. Chances are that your burning desire for Cool Ranch Doritos has nothing to do with your adrenal glands and everything to do with, well, your burning desire for Cool Ranch Doritos.

You're going to eat again. It's inevitable. But take comfort in the fact that reaching for that slice of pizza, whether you're legitimately hungry, feeling stressed, or indulging a craving, has less to do with your lack of self-control and self-discipline than with biological and psychological cues that you may not even be aware of — until now.
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