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Why you crave junk food and how to make it stop

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When it comes to eating junk food, unaddressed hunger and fatigue do come back to bite us.

QUESTIONI get home hungry at 5pm and often find myself going for junk food, like potato chips, instead of a healthier snack. Why don’t fruit or veges have a similar appeal?

ANSWEROur appetite and food choices are often guided by our subconscious rather than our conscious brain. Unfortunately, our subconscious brain doesn’t care about our personal goals, like avoiding junk food or reclaiming our youthful figure – it’s focused on one thing: survival.

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A hungry brain wants food, a lot of it, and isn’t satisfied by low-calorie snacks, says obesity and neuroscience researcher Stephan Guyenet in his book The Hungry Brain: Outsmarting the Instincts That Make Us Overeat.

Having not eaten since breakfast, Guyenet cycled to the University of Washington in Seattle at 4pm one day for an experiment that appeared in his book. He was to view images of low-calorie healthy food and high-calorie junk food, as well as non-food images, while inside an MRI machine that measured his brain activity. Guyenet’s brain lit up like a Christmas tree at the sight of high-calorie food such as pastries, pizza and chips. The same did not occur when he was shown fruit and vegetables or non-food objects. Why?

The most likely explanation is that our brain doesn’t want low-calorie (healthy) food when it’s hungry. As Guyenet says in his book, in a hungry state, our subconscious brain has a powerful drive towards calorie-dense foods that offer quick, easy, concentrated energy.

It stands to reason. Why would the brain choose a low-energy lettuce leaf over a high-energy slice of pizza? That doesn’t make sense from a survival perspective.

No matter how hard you try, if your brain thinks it’s starving – thanks to a restricted diet or restricted eating during the day – it will eventually wear you down. The solution is not to sharpen your willpower or stock up on healthier snacks (though that might help) but, rather, to ensure your body knows it’s not starving. According to Guyenet’s research, we can do this by eating food during the day that sends strong satiety signals to the brain.

Eating food that’s high in protein and/or fibre helps us feel fuller for longer. For breakfast, for example, you may have eggs on wholegrain toast, or greek yogurt with wholegrain muesli and fruit (greek contains more protein than other yogurt). Aim to be comfortably full, but not overfull, after a meal.

Look at your sleep quality and quantity too. A sleep-deprived brain behaves much like that of someone who’s hungry. Researchers have found, through MRI scans, that the brains of sleep-deprived people are more responsive to images of high-calorie junk food. Clinical trials have confirmed that people who are short of sleep consume more calories.

So, if you’re not enjoying regular, restful sleep, do something about it. And if you’re not eating enough during the day, do something about that as well. Ensure you’re acknowledging and responding to hunger, rather than ignoring it and allowing it to become an uncontrollable urge to overeat by late afternoon or the evening (that post-dinner bingeing could also be a rebound from a day of dietary restriction). This may mean adding a mid-morning or mid-afternoon snack to your daily diet.

When you’ve dealt with poor sleep and hunger, you’ll be better able to make healthy food choices at 5pm, but if your body still demands the crunch of a potato chip, don’t sweat it – have a few and enjoy them. Maybe try prepping some vege sticks the night before, though, and grabbing some raw nuts to enjoy with them to provide a balance of nutritious and easy foods. Remember, healthy eating is not only about nutrition but also about enjoying food and having a comfortable relationship with it.

This article was first published in the April 7, 2018 issue of the New Zealand Listener.