How Junk Food Reshapes Teens’ Developing Brain

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The adolescent brain has strong impulses toward reward, poor behavioral control, and a high possibility of being shaped by experience. This is often manifested in difficulty in resisting high-calorie junk food.


Obesity is on the rise around the world, especially in children and adolescents. In 2019, there are more than 150 million obese children worldwide. They have an increased risk of heart disease, cancer and type 2 diabetes.

Adolescents who are obese are likely to remain obese as adults. If the current trend continues, 70 percent of 40-year-old adults could be overweight or obese by 2040.

I’m a neuroscientist, and my research focuses on how food changes the brain. I want to understand how bad eating habits affect brain development, and also why young people today are so prone to obesity.


Teens are the biggest consumers of high-calorie junk food. During puberty, many children have an insatiable appetite, because rapid growth requires a lot of energy. Rapid metabolism and growth spurts provide some protection against obesity. But excessive consumption of high-calorie junk food and a sedentary lifestyle can counterbalance any metabolic protection.

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The Adolescent Brain is Vulnerable

Adolescence is a pivotal period for brain development. Adolescence coincides with a new social autonomy and independence which makes it possible to make personal food choices.

During adolescence, the connections between different regions of the brain and individual neurons are in the process of refinement and strengthening. The adolescent brain is malleable due to increased “neuroplasticity”.


This means that the brain is very receptive to remodelling by the environment, which includes food. These changes can remain scheduled after development is complete. The adolescent’s brain is therefore vulnerable to changes induced by food, and these changes can last a lifetime.

Resisting Junk Food is Not Easy

Neuroscientists use functional brain imaging to examine how the brain responds to events. Brain scans show that the prefrontal cortex – a key area of ​​the brain for behavioral control and decision-making – does not reach full maturity until the early twenties.

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The feeling of reward after eating food can be exaggerated due to the increased number of dopamine receptors in the adolescent brain… (Shutterstock)

The prefrontal cortex controls the impulses triggered by what surrounds us and makes it possible to resist them. For teens, it can be particularly difficult to refrain from swallowing a whole bag of candy or buying junk food.


An Insatiable Need For Rewards

Unlike the immature prefrontal cortex, the brain’s reward system – the mesolimbic dopaminergic system – is fully developed at a much earlier age.

Teens are particularly drawn to rewards, such as sweet, high-calorie foods. This is caused by an increased number of dopamine receptors in the adolescent brain, so the feeling of reward can be exacerbated. Frequent stimulation of the reward circuit leads to lasting brain adaptations.

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During adolescence, these changes can trigger long-term changes in the balance of chemicals in the brain.


Overall, the adolescent brain has an overwhelming desire for reward, poor behavioral control, and a propensity to be influenced by experience.

This manifests as a difficulty in resisting rewarding behaviors. It is therefore not surprising that adolescents prefer to eat foods that are easy to obtain and that quickly bring a feeling of reward, even if they know that it is harmful to health. But what are the long-term consequences for the brain?

Transcranial Magnetic Stimulation

Functional imaging studies show brain activity during tasks or viewing food images. The food reward brain circuits are more active in obese adolescents than in those of normal weight.


It is interesting to note that there is also a lower activity in the prefrontal cortex. Obesity can both increase the activation of the reward system and reduce brain activity in the centres that control the desire to eat.

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However, weight loss in teens restores activity levels in the prefrontal cortex. The prefrontal cortex is, therefore, a key area of ​​the brain to control food intake, and the change in diet increases activity in the areas of the brain responsible for self-control.

Physical exercise increases the plasticity of the brain. (Shutterstock)

Transcranial magnetic stimulation (TMS), which allows scientists to modify brain activity in the prefrontal cortex, can change the inhibitory regulation of eating behavior. Treatment with repeated SMT could be a new therapy to restore cognitive control of the diet, which would lead to lasting weight loss.


Exercise Increases Brain Plasticity

Excessive consumption of junk food during adolescence can alter brain development and lead to long-term poor eating habits. But, like a muscle, the brain can be exercised to improve willpower.

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The great plasticity of the brain during adolescence makes it more receptive to changes in lifestyle. Physical exercise stimulates brain plasticity, helping to develop new healthy habits. By understanding the way in which obesity modifies the brain, we can have avenues for intervention.

Functional brain imaging adds a new layer of information that allows clinicians to identify people at risk and track changes in the brain during changes in diet and lifestyle.


What is more, SMT could constitute a new therapeutic approach to improve the recalibration of the young brain in order to prevent transformations that will remain in adulthood.

This article is republished from The Conversation under a Creative Commons license.

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