The lure of the fast-food joint often proves too much—don’t be too hard on yourself, though, because junk food contains an unholy trinity of the nutrients your body craves the most.
Your body is biologically hardwired to crave sugar, fat, and salt to survive potential famine. Sugar is released by the body as fast-acting energy; fat gives an incredibly concentrated supply of long-lasting fuel; and salt is essential for body-fluid balance. These were typically quite difficult foods for our hunter-gatherer ancestors to find, and no single naturally occurring food contains these three enticements together. So when you get your hands on a fast-food burger, with its sweetened bun, sugary dressing, and meat loaded with salt and fat, a strong, triple-whammy biological craving rises up in you.
Compounding this, eating sweet-fatty-salty foods delivers a short but powerful dose of the rewarding brain hormone dopamine—the very same substance that makes you feel good after sex, winning the lottery, or watching your favorite sports team win a match. Dopamine is one of the main brain chemicals that drives addictions, so it’s no wonder a habit of eating junk food can be difficult to drop.
And to make matters worse, the hormone responsible for hunger, ghrelin, also sticks itself to dopamine cells in the brain, making the prospect of eating that glistening, sugar-topped doughnut increasingly irresistible the hungrier we get. We long for it like a dog does a juicy bone. Our brains begin to anticipate the hormonal rewards so that even before the clock says it’s snack time, the feel-good flight is already accelerating down the runway, and putting a stop on it gets harder and harder!
Eating into your allowance
Fast food is quickly eaten and not filling but can swallow up a surprising proportion of your daily nutrition needs. A small bag of chips claims more than 10% of the recommended fat amount for adults, a burger almost half of the salt, and a can of cola more than three-quarters of your sugar total.
Want to triumph over junk food?
■ Make sure your diet includes plenty of high-fiber vegetables to keep you sustained for longer and keep the hunger homone ghrelin at bay.
■ avoid eating when stressed because the hunger hormone ghrelin surges powerfully as part of the body’s stress response, which is why we are greedy for feel-good food after an intense day.
■ choose a less tempting route home, because just traveling past a fast-food outlet sign can be enough to trigger your brain to release anticipatory pleasure hormones, long before you smell fried food!