Obesity is increasing
worldwide,
especially among
children and teenagers. In 2019,
more than 150 million children
in the world were obese. These
children are at increased risk of
heart disease, cancers, and Type
2 diabetes.
Teenagers with obesity are
likely to remain obese as adults.
If these trends continue, 70 per
cent of adults aged 40 years could be either
overweight or obese by 2040.
I am a neuroscientist and my
research investigates how diet
changes the brain. I want to
understand how unhealthy
diets impact the developing
brain, and also why
young people today
are so prone to developing
obesity.
Adolescents
are the greatest consumers
of calorie-rich “junk” foods. During
puberty, many children have an insatiable
appetite, as rapid growth requires
lots of energy. Heightened metabolism
and growth spurts can protect against
obesity, to an extent. But excessively
eating high-calorie junk foods and increasingly
sedentary lifestyles can outweigh
any metabolic protection.
The Teenage Brain
Is Vulnerable
The teenage years are a key window
of brain development. Adolescence
coincides with a new-found social autonomy
and the independence to make
personal food choices.
During adolescence, connections
between different brain regions and individual
neurons are also being refined
and strengthened. The adolescent brain
is malleable because of increased levels
of “neuroplasticity.”
This means the brain is highly receptive
to being shaped and rewired by
the environment — including diet. In
turn, these changes can become hardwired
when development is complete.
So the adolescent brain is vulnerable to
diet-induced changes, but these changes
may endure through life.
26 WNY Family July 2020
How Junk Food
Shapes the
Developing
Teenage Brain
— by Amy Reichelt
Resisting Junk Food
Is Tough
Neuroscientists use functional brain
imaging to examine how the brain responds
to specific events. Brain scans
show that the prefrontal cortex — a key
brain area for behavioral control and
decision-making — doesn’t fully mature
until the early 20s.
Feelings of reward after eating food
can be exaggerated due to increased
numbers of dopamine receptors in the
teenage brain.
The prefrontal cortex controls and
overrides urges triggered by events
in the environment. Resisting eating
a whole bag of candy or buying cheap
junk foods can be particularly difficult
for teenagers.
Voracious Drive
for Rewards
In contrast to the immature prefrontal
cortex, the brain’s reward system —
the mesocorticolimbic dopamine system
— is fully developed at a much earlier
age.
Teenagers are particularly drawn to
rewards, including sweet and calorie-
dense foods. This is due to increased
numbers of dopamine
receptors in the adolescent
brain, so the feeling of reward
can be exaggerated. Frequent
stimulation of the reward system
results in enduring brain
adaptations.
During adolescence, these
changes may cause long-lasting
shifts to the balance of brain
chemicals.
Taken together, the teenage
brain has a voracious
drive for reward, diminished
behavioral control
and a susceptibility to
be shaped by experience.
This manifests
as a reduced ability
to resist rewarding
behaviors. So
it’s not surprising
that teenagers
prefer to eat foods that are easy to obtain
and immediately gratifying, even in
the face of health advice to the contrary.
But what are the enduring brain consequences?
Transcranial
Magnetic Stimulation
Functional imaging studies show
brain activity during tasks or viewing
images of foods. Brain circuits that process
food rewards are more active in
adolescents with obesity compared to
those considered normal weight.
Interestingly, lower activity is seen
in regions of the prefrontal cortex. This
shows that obesity can both heighten activation
of the reward system and reduce
brain activity in centers that can override
the desire to eat.
Importantly, successful weight loss
in adolescents restores levels of activity
in the prefrontal cortex. This provides
critical knowledge that the prefrontal
cortex is a key area of the brain for
controlling food intake, and that diet
interventions increase activity in brain
regions that exert self control.
Transcranial magnetic stimulation
(TMS), a way scientists can modify
brain activity in the prefrontal cortex,
can change inhibitory control of eat-