You’ll be happy (or dismayed) to learn that your willpower never stood a chance against those crunchy, chocolaty morsels. See, biscuits – and other fat-laden eats – stimulate your brain’s reward system and set off a neural pattern that makes you want to scoff more, says former US Food and Drug Administration commissioner Dr David Kessler, in his exposé The End of Overeating (amazon.com). Dr Kessler and WH weight loss expert, dietitian Sharon Carey, reveal why all reason flies out of the window when you’re face-to-face with a naughty food. It’s all about that reward system.

Here’s how it works: the first time you ever ate a Tim Tam your brain registered the enjoyment of the unique taste sensation by flooding you with the pleasure chemicals dopamine and serotonin. That’s the reward system and it’s essential to human survival. “It encourages us to keep seeking out enjoyable things like sex and food,” says Dr Kessler. “Powerful biological forces make us pursue them and feel momentarily better once we obtain them.” If you’re unsure just how powerful the urge is, consider this: when lab rats were given the chance to electrically stimulate the nucleus accumbens, the brain’s pleasure centre, they hit the lever thousands of times in an hour, showed no interest in food or mates and eventually died of exhaustion. It’s the anticipation of those feel-good chemicals that prompts you to pick up “just one more” biscuit, even though you’re not hungry. As addiction counsellor Gillian Riley explains in Eating Less ($26.95, Ebury Press), “Our brains get the message that fats and sugars are more rewarding than vegetables – the more we eat them, the more we reinforce our attraction.” The extra problem, adds Carey, is that we’ve also conditioned ourselves to see food in packets as everyday foods when, in fact, they are the exact opposite.

Susannah Paterson, a psychotherapist who specialises in treating eating disorders, says, “Rewarding foods are reinforcing, which means we grow to expect them, like when we train puppies with treats.” And their reinforcement value increases with associated cues, like wanting a croissant when you walk past the bakery. Your cue triggers your reward system to release dopamine, which you notice as an urge or craving, which you satisfy by buying the treat. “This pattern sets up pathways in your brain, and each time you repeat the cycle, the pathway is reinforced, much like wearing a groove into a footpath,” explains Paterson. You eat automatically and don’t realise you are firing off a well-worn neural pathway and that your brain chemistry is in control of your eating habits.

Another reason you can’t stop at just one: human beings have what food-industry insiders call a “bliss point”, a nirvana of the tastebuds triggered by particular amounts of sugar, salt and fat. Trouble is, an overload of those ingredients makes junk food “hyperpalatable” – a taste experience so intense that it kicks the brain’s pleasure system into overdrive. It’s like a drug and leads you to obsess about that moment of pleasure so much that you’ll do almost anything to prolong or relive it.

Settling point

Scientists are still trying to understand the effects of overeating on our hormones and appetite. In the 1980s they developed the “set-point theory” – the idea that there’s a genetically determined ideal weight, which your body naturally controls. The system is not perfect, as dietitian Dr Joanna McMillan Price explains: “There are more hormonal regulators telling the brain that the body is losing weight than the reverse. When you restrict kilojoules, your system protects you from starvation by increasing your appetite. But it doesn’t reduce your appetite in the same way when you gain weight to get back to your set point. That’s because obesity wasn’t a problem for our ancestors, but prolonged scarcity was.”

Dr Kessler thinks it’s more useful to think of having a “settling point” instead. He believes that lots of factors determine what you weigh: genetics, bone structure, how often you work out. Overlooked is how much you feel compelled to eat and how much food is available to satisfy your urges. And these days food tends to find us.

Chowing down on junk pushes up your settling point. You can’t burn enough energy to keep up with all that reward-driven grazing. Other factors, such as rapid weight loss from strict dieting, or reduced exercise, will also contribute to weight gain, says Carey, so you need to get deceptive and “trick the body into thinking there isn’t a famine ahead in order to crave less.”

Go on, you deserve it

If you’re plagued by cravings for fatty food, you’ll know how easy it is to give in. “Food is the only addiction we cannot abstain from completely, and the food advertising industry behind it is worth billions,” Carey says. Bridget Kelly, a dietitian who specialises in food marketing, points out that products geared specifically towards women are cleverly marketed to appeal to our emotions. “There’s no way to pretend they provide essential nutrition, so the focus is on giving yourself a treat and suggesting you are being deprived if you have to go without,” she says. Sweet treats play with the language of seduction and desire, and sensuous words like “decadent”, “luxurious”, and “heavenly” abound. And when you succumb you’ll find those taste sensations have been carefully choreographed to provide maximum impact. You’ll quickly reach your bliss point, sending your brain and body back down the well-travelled path.

Please release me

So, if it’s your reward system and not your natural appetite that dominates what you chow on, how do you break the cycle? You can’t stop receiving cues to eat, but Dr Kessler says you can “learn to distrust your urges”.

“Thought stopping” is a term coined by Richard Rawson of the University of California, who works with recovering drug addicts. He explains that you need to make an instant decision to say “no”. Once you begin the debate: “Should I or shouldn’t I?”, you’ve lost the battle. “It’s like TV,” says Rawson. “Change the channel.”

Overeating tends to be impulsive – it’s unlikely you planned to inhale the packet of Tim Tams. So give yourself some food rules, says Paterson. “Tell yourself: ‘I don’t eat cheesecake,’” she says. “Rules set up internal boundaries, and they help build stronger inner resources. Each time you don’t follow through with the urge, you are gradually put back in control.” In his book Real Weight Loss ($24.99, craigpotton.co.nz), Dr Doug Sellman, professor of psychiatry and addiction medicine at the University of Otago, suggests “urge surfing”. Remember that urges or cravings do not last forever, so just feel the urge, don’t fight it and watch it come and go like a wave.

You are not my friend

It’s also vital to change the way you look at all those guilty pleasures. See a box of doughnuts not as your dreams come true but as sugar and fat covered in more sugar and fat. Smoking was once glamorous, but now we see it as addictive and dangerous. It’s possible to shift your view of rewarding food as well. “The good news is, if you practise eating healthy foods on a regular basis, you’ll eventually feel rewarded for choosing them,” adds Carey.

“You have to find other sources of emotional reward, particularly when you’re stressed,” says Paterson. Exercise is the supremo stress-buster (surprise, surprise) and gives you that delicious hit of dopamine and serotonin, and the satisfaction of doing something positive for your body.

Many nutrition experts agree that one of the worst things you could do is to radically restrict your eating. “Research has shown that people who believe they are about to go on a diet will eat far more junk food, if offered, than non-dieters,” says Carey. “It’s a kind of ‘Last Supper’ effect, stocking up for a famine.” Instead, she recommends filling up on wholesome, natural foods, while allowing just a taste of the not-so-good from time to time. “Try taking two minutes to eat one raisin by thinking about the whole experience – colours, textures, smell and taste. It may be all you need to satisfy your sugar craving, and you’ll increase your awareness of how quickly and mindlessly you usually eat!”

In the end, lasting change rests on viewing hedonistic delights as your enemy, not your best friend. There’s a huge discrepancy between the anticipation of and the actual experience of a junk-food binge, after which you’re never pleased with yourself. Instead of feeling weak, guilty or embarrassed, recognise that you’re in a trap. It’s liberating to know that you can break the cycle once you recognise it’s happening. It’s a biological challenge and, with a mindful attitude, you can reduce the lure of scarfing too many Tim Tams for good. Plus you’ll have rewired a better, more resilient brain into the bargain.