Warning! Junk foods can harm a teen’s brain.

Written By Sharon Oosthoek.

Though hard to resist, these foods pose risks to learning and mental health


Adolescent brains have a hard time resisting junk food. Researchers now are showing that high-fat and high-sugar diets — such as burgers, fries and sweets — can lead to disturbing changes in mental health.

“You are what you eat.” When people say that, they mean a healthy diet can boost your health. But the opposite is also true. In fact, if you’re between the ages of 10 and 19, eating too much junk food can harm your body and your brain.

Junk food shapes adolescent brains in ways that impair their ability to think, learn and remember. It can also make it harder to control impulsive behaviors, says Amy Reichelt. It may even up a teen’s risk of depression and anxiety, she notes.

Reichelt is a brain and nutrition specialist at Canada’s Western University in London, Ontario. Adolescents are more sensitive than any other age group to foods with a lot of processed fat and sugar, she says. She is part of a group of scientists around the world who have been studying why.


She and two other researchers at Western recently reviewed more than 100 studies (including their own) about how poor food choices can impact adolescent brains. They described what they learned in the May issue of The Lancet Child and Adolescent Health.

One problem: Adolescent brains are not yet fully formed. And that actually leads to three problems in one, says Reichelt. First, adolescent brains are still developing the ability to assess risks and control actions. Second, teen brains get more pleasure than adult brains do from rewarding behaviors such as eating junk food. Third, adolescent brains can be more easily influenced by their environment. This can include any stress you’re feeling, any isolation or any drugs you may be taking. It can also be influenced by diet. Together, these all can combine to make junk food both hard to resist and extra bad for teen health.

Brains under construction

 

The prefrontal cortex region of the brain (shown here in green) isn’t fully mature until we are in our 20s. That’s a problem for adolescents. The prefrontal cortex helps us understand risk and resist bad behaviors, such as eating an entire bag of chips.DORLING KINDERSLEY/GETTY IMAGES PLUS

Let’s break that down, starting with preteen and teen behaviors. The brain region that tells us we shouldn’t eat chips all the time — and helps us resist that urge — is the last to mature. Called the prefrontal cortex, this region doesn’t fully develop until we are in our early 20s.

Brain imaging studies show that the prefrontal cortex turns on when we weigh risks and make decisions about how to act.

“Most of our complex brain functions happen in the prefrontal cortex,” says Reichelt. This includes complex math and reading. But she notes that it also includes “how to assess risky behavior.”

At the same time, teen brains get more buzz from rewards. Unlike the prefrontal cortex, the parts of the brain that make us feel good when we do something pleasurable — like eating tasty foods or being with friends — are fully developed by the teen years.

In fact, these regions are even more sensitive when we are young. That’s because of a natural chemical called dopamine (DOH-puh-meen). Dopamine is sometimes called the “feel good” chemical. It lifts our mood when we experience something rewarding. And it is especially active in adolescent brains.

Explainer: What is neurotransmission?

As a neurotransmitter, it zips across the spaces between brain cells. Once it arrives at a new cell, dopamine binds to docking stations there. These molecules are known as receptors. When dopamine docks, those receptors relay the “feel good” signal from the last cell to this new one. That tells the brain that whatever it just experienced is worth getting more of. Adolescents have more dopamine receptors in the brain than do adults. So they get more good vibes from anything they find enjoyable.

The teen brain, thus, has two strikes against it when it comes to resisting junk food. “It has a heightened drive for rewards and reduced self-regulation,” says Reichelt.

That’s a big problem for adolescents because of the third issue: Growing brains can be more easily changed by eating high-fat, high-sugar foods. That’s what Reichelt and her team discovered in their studies of “teenage” mice.

Mouse brains on fat and sugar

Since mouse brains develop very much like our own, they can be used to understand how what we eat affects the human brain. In 2017, Reichelt was part of a team that fed adolescent mice high-fat foods to see how it affected their brains.

One group of mice ate a diet in which 63 percent of their calories came from fat. (That’s a lot of fat. It would be like eating bacon cheeseburgers and ice cream every day.) A second group ate a healthy diet.

Source: https://www.sciencenewsforstudents.org