The next time your teen goes out for fast food or reaches for something quick from the cupboard, you may want to suggest making a salad, or grabbing a piece of fruit.

A new review paper out of Western University looked at how poor dietary choices can change an adolescent's brain.

Researchers looked at that time in a person's life between puberty and adulthood, and how still developing decision-making capabilities, limited restraint and a heightened reward system can contribute to poor eating choices, which in turn can change their brain.

We're talking about high-fat, high-sugar food that fill the menus of fast food restaurants and snack aisles at the grocery stores.

Understanding a 'brain without brakes'

"When the brain is maturing, it goes through its final stages up until the mid-20s," said senior author Amy Reichelt, a BrainsCAN Postdoctoral Fellow at Western's Schulich School of Medicine & Dentistry.

"The final part of the brain to mature is the prefrontal cortex and this area of the brain is vital for behavioural control and decision making."

Reichelt says because that area of brain isn't yet fully operational, teens are more likely to consume unhealthy foods that their brain deems highly rewarding.

"The teenage brain has a fully-developed reward system like an adult, so it experiences the same amount of reward and then it doesn't have the same amount of top down executive control or behavioural control that allows you to inhibit that behaviour that can make you overconsume." she said.

To put it simply, Reichelt says teens don't have the same "off switch" that makes them stop eating.

The dangers of overstimulating a teen's reward system

Research shows that over time, the excessive or overconsumption of junk food can lead to changes in the structure and function of the prefrontal cortex. Those changes include altering dopamine signaling and inhibition.

"If a behaviour is rewarding, dopamine makes us want to carry out that behaviour again," said Reichelt. "Adolescents have increased numbers of dopamine receptors in the brain, so when they do experience something rewarding, that experience of reward and how the brain processes it is heightened compared to that of an adult."

The paper warns that overstimulating a teen's reward system with poor dietary choices can lead to poor cognitive control and heightened impulsivity as they enter adulthood.

"I think that it's really important for young people to understand the impact that these diets are having on their brain, that it extends beyond your physical health for your body, but encapsulates basically every aspect of brain function," said Reichelt.

She added that includes a teen's attention span in school, learning new information, remembering new information and being able to regulate their mood.

"It's got a huge impact on mental health for people as well," she said. "For young people who are experiencing any kind of mental health conditions such as depression or anxiety, diet should be one of the first things that they look at in being able to make positive changes for their brains and mental health."

The review paper was recently published in the journal The Lancet Child and Adolescent Health and was written by Cassandra Lowe, J. Bruce Morton and Amy Reichelt.