Why we crave junk food and how to turn down the cravings

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Junk food is delicious. As a “food group,” it’s pretty much the most delicious there is. That’s why it’s on the top of the food pyramid, I think. All the other food groups worship it because it’s the most delicious.

It also happens to be the most ridiculously persuasive food group our brains have ever had to fight against.

My brain knows that junk food is not good for me, won’t make me feel good and won’t help me build a healthy lifestyle. Eating junk food has even been linked to higher risks of depression. And yet, my brain doesn’t stop me eating it, even when I know these facts are true.

Here’s the really good news, though: understanding why we get cravings for junk food and how they affect our brains can actually help us to put in place systems that will override or curb those cravings. But first, let’s take a look at why we get junk food cravings in the first place.

Why we crave junk food

Food pleasure is something we get from a combination of caloric stimulation by micronutrients (protein, carbohydrates and fat), and sensory factors:

Sensory factors that most contribute to pleasure are salty taste, sweet taste, umami taste [from MSG], and orosensation from the oral cavity (feeling).

Food scientist Steven Witherly explains in Why Humans Like Junk Food that as a general rule, we are drawn to high-calorie foods more than low-calorie alternatives. When we look at a food option, our brain calculates how much pleasure we’ll derive from eating and digesting it. Our main aim is to maximize pleasure based on both food sensations and macronutrient content.

What I found really interesting about this process is that our bodies will not necessarily prefer a “light” option (e.g. light ice cream or reduced fat potato chips), when the pleasure in eating the food matches that of a standard alternative. If ice cream feels as pleasurable to eat whether it’s light or regular, our bodies will cry out for the higher-calorie option.

Witherly says elements like salt, sugar and MSG contribute the most to our “food pleasure”:

Many of our favorite foods are supernormal combinations of salt, fat, and sugar that exceed anything available to our wandering ancestors.

Contrasts of flavor, texture, color and appearance are the most important contributors to food pleasure, second only to taste sensations.

Ice cream is a great example of a junk food that we enjoy because of its caloric content, sensory factors and contrasts. Our brains react to the texture of ice cream as it melts in our mouth (the same way we enjoy the textures of chocolate and popcorn), the temperature which starts off cold and warms up in our mouths (providing contrast), and the fact that ice cream is an emulsion—a mixture of liquids that normally can’t be mixed together, such as butter, a mixture of water and fat.

Of course, ice cream is also loaded with sugar, fat and salt. Plus, studies have shown that the flavor of vanilla doesn’t cause flavor burnout in the brain, the way other, stronger flavors often can, so vanilla ice cream is especially enticing to our brains.

Why willpower won’t keep the sugars away

So we know we’re drawn to foods that are full of sugar, salt and fat, and especially those that combine a variety of texture and color contrasts. But why can’t we rely on simple willpower to help us avoid eating those foods?

The problem is, willpower is a finite resource and we just don’t have enough of it.

The prefontal cortex (the section of the brain right behind your forehead) is the part that helps us with things like decision-making and regulating our behavior. Self-control, or willpower, is taken care of in this part of the brain as well.

prefrontal-cortexKelly McGonigal, author of The Willpower Instinct, says willpower is a response that happens in both the brain and the body.

The willpower response is a reaction to an internal conflict. You want to do one thing, such as smoke a cigarette or supersize your lunch, but know you shouldn’t. Or you know you should do something, like file your taxes or go to the gym, but you’d rather do nothing.

Each time we have one of these conflicts, like choosing something healthy to eat for breakfast when we want to eat sugary cereal instead, our willpower gets depleted from the effort.

McGonigal points out that one of the most replicated findings about willpower is that it seems to be finite—that is, we only have so much and it runs out as we use it:

Trying to control your temper, ignore distractions or refuse seconds all tap the same source of strength.

We can look at willpower like a muscle—it can get exhausted by overuse, but just like our physical muscles, there are some researchers who believe we might be able to strengthen our willpower by training it.

There are other ways we can strengthen our willpower resource, such as making decisions for ourselves in advance (it’s easier to eat the healthy breakfast if it’s in front of you, ready to go in the morning) and limiting the effort we spend on minor decisions. Barack Obama offers a good example: he limits his suits to only black and blue, so the decision of what to wear never takes much out of him in the mornings.

Lastly, like most things in life, getting a good night’s sleep can help us build up a defense against junk food cravings.

How the brain regulates junk food cravings

We crave junk food more when we’re tired, according to a study from UC Berkeley.

Those areas of the brain that are required for willpower are also the ones we use for judgement and decision-making. You can imagine they’re pretty important when it comes to avoiding junk food.

Sadly, a lack of sleep affects these areas, making them “blunted,” according to the Berkeley study. The sleepier we are, the more we struggle to make sound decisions and exercise self-control.

Even worse, sleep deprivation actually amplifies the areas of the brain that are linked to motivation and desire. Which means our self-control is inhibited, and our desire signals are stronger than normal. What a terrible combination in the face of delicious, sugary donuts!

The study found that high-calorie foods were more appealing to participants when they were sleep deprived, compared to their normal state after a full night’s sleep.

On the upside, high-intensity exercise has been found to turn down our junk food cravings, at least temporarily. A study published in the American Journal of Clinical Nutrition asked volunteers to run at speed for an hour, after which their brains were scanned to test for activity in the insula—the “primary taste cortex” of the brain.

Activation in this region is increased in the anticipation of foods, and when consuming foods that we perceive as being pleasant.

The volunteers’ brains were also scanned after an hour spent resting. Each time, the participants viewed pictures of high- and low-calorie foods.

Our findings showed that activation in the insula was reduced when looking at pictures of high-calorie foods such as pizzas, burgers and doughnuts, following exercise.

Overall appetite was found to be lower on average after high-intensity exercise, as well. The researchers suggested that the results could point to the body prioritising hydration after exercise, and thus being drawn to the high water contents of low-calorie foods like carrots, strawberries and apples. The insula does play a role in regulating thirst, so this could be the case.

Either way, high-intensity exercise could be a good way to curb cravings for high-calorie snacks. If that seems like a lot of effort, you might want to try the scientific, 7-minute workout.

How building habits can help us eat healthier

So here’s the really good takeaway from all of this: although we don’t have the willpower to overcome the cravings we get for junk food, there’s actually a better way to stop them attacking us all the time: building habits.

During times of stress, or when we’re overwhelmed or tired, our willpower is depleted. This doesn’t necessarily mean we’ll be more likely to eat junk food, though—it’s a bit more nuanced than that. A study by the University of Southern California found that when we’re lacking in willpower, we’re more likely to fall back on old habits—whatever they are.

Habits don’t require much willpower and thought and deliberation. – Wendy Wood, USC professor

The study tested college students to see what their routines looked like during stressful periods, such as exam time. Those that ate junk food for breakfast during the semester were more likely to do so during exam time when they were stressed or tired. The students who ate healthy breakfasts as a habit, however, were more likely to eat healthy food during the exam period. The same went for those with habits of reading the newspaper and going to the gym.

So if we really want to avoid those junk food cravings, we need to put healthy habits in place. Wendy Wood, one of the researchers who led the study at USC said actions need to be repeated to become habits:

What we know about habit formation is that you want to make the behavior easy to perform, so that people repeat it often and it becomes part of their daily routine.

Weight Watchers CEO, David Kirchhoff, agrees, after spending a long time building up a habit of eating healthy foods for breakfast:

Is it because I’m disciplined? No, it’s because I do it so many times in a row I can’t remember how to do anything else.

Lastly, an important part of developing strong habits is your environment. A study published in the American Journal of Public Health showed that putting healthy foods in high visibility areas of a cafeteria and making it easier to access them increased the amount of times people chose those foods over less healthy options.

choice architecture

Source: American Journal of Public Health

You can make use of this information as you build your own habits. Putting healthier foods on the shelves at eye-level in your house will make you more likely to see them first. Preparing healthy snacks in advance will make them easier to choose when you’re hungry. And setting out a healthy breakfast the night before will make your morning choices simple.

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