How to stop craving junk food

Why do you reach for a third slice of pizza when you’re already bursting out of your jeans?

Knowing the signals of hunger, the cues for stress eating, and what triggers your cravings will help you tame all three.

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 a hamburger with bacon and cheese 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 4pm Tim Tam? 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. Here, we bring you the science regarding how appetite develops in our bodies – and the news on what might make your hunger 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 jaffles. Or chicken laksa. Or that half-eaten muesli bar in your desk drawer. 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 of you reproducing. Bad survival strategy.

It’s important to note here that the drive to eat as much as we could, whenever we could, was spawned long before there were Violet Crumbles, Krispy Kremes, or Big Macs. And even as we evolved into a world of giant portions and 24-hour takeaway joints, our basic bodily urges remained in the prehistoric era.

Now that hunting and gathering has more to do with stocktake 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 hell of a genetic deck stacked against us.

If we understand just how the genetic deck is stacked, we can get a better grip on handling hunger. Science has nailed the basics. That pre-lunch 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 Dr David E Cummings, of the University of Washington. 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.

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Hungry hormones

It’s called ghrelin. It sounds like something you shouldn’t feed after midnight, 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-biscuit 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 discovered that the shots increased food intake by 20 per cent in the lean group and by a whopping 70 per cent 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 eating plan: 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 2pm, 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 able to walk past a cafe 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 your presentation and head to the deli for that ham and cheese jaffle (on wholegrain with tomato). You take the first bite and digestion begins.

When the sandwich reaches your stomach, your body begins to absorb the nutrients, and your ghrelin levels start to go down. Once it 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 for later.

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 per cent 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 Christmas, 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 kilos off. But others say hitching hunger to one hormone is too simple.

“Hormonal regulation of appetite is an extremely complex area,” says Dr Arline Salbe, a research nutritionist with the National Institutes of Health in the US. “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 many people who lose weight eventually gain it back again.

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 two years ago by researchers, obestatin apparently contributes to satiety by slowing the speed at which food travels through your digestive system. In a Stanford University 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 pharmaceutical company that funded the research.

The scientific community is still trying to identify exactly 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.

The stress factor

There’s more to appetite than the steady ebb and flow of hunger hormones. Having a tough day always makes it harder to walk by the brownies your colleague has so thoughtfully brought to work, even when your body isn’t really hungry. The same urge to snack when stressed happens to rats, says Dr Mary Dallman, a physiology professor at the University of California.

“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 makes them eat more and sends them right to high-kilojoule bad-for-them stuff.

It turns out that humans and rodents have similar primal brains where the control centres for both hunger hormones and the stress hormone cortisol live. When your body is low on energy or stressed, 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 fossicking 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.

“There’s a clear difference between hunger and cravings,” says Dr Eva Kemps, senior lecturer in psychology at Flinders University in Adelaide, who studies food cravings.

“Hunger is physiological – we need to feel it in order to survive. Cravings usually happen when you don’t need food on a physiological basis. They’re more psychological – triggered by negative emotional states like boredom or depression, or by factors in your environment such as when you walk past a bakery or see food advertised on TV. There are always food cues around us, so if you’re sensitive it could trigger a craving.”

Maybe it’s the chocolate bar you eat to fight the mid-afternoon slump, the after-dinner biscuits, or the chips you like to munch during your favourite TV show. Pretty soon you’re like one of Pavlov’s dogs. You hear the bell – or the opening chords of the Grey’s Anatomy theme tune – 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 a tub of Cookies & Cream.

“Whether it’s a craving for drugs, or chocolate, or shoes, the mechanism in the brain is the same,” says Dr Marcia Pelchat of the Monell Chemical Senses Center in Philadelphia.

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

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 than with biological and psychological cues that you may not even be aware of – until now.

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