BMIs. However, the team also found that eating a diet high
in omega- 3 fatty acids promoted relational memory skills
(American Journal of Clinical Nutrition, 2014).
University of Illinois researchers also explored how the
type of body fat may affect cognitive changes, finding that
overweight children ages 7 to 9 years with more belly fat did
worse on tests of hippocampal-dependent relational memory
(The Journal of Pediatrics, 2015).
Research suggests that obese children have more health
problems and are absent from school more often, tend to
come from families of lower socioeconomic status, and face
social stigma, all factors that may affect academic performance.
Animal studies, though, buttress the evidence that obesity
changes young brains, and studies in children so far have looked
at similar cognitive functions, Davidson says.
“You’re seeing impairments in the kinds of tasks which
would make it more difficult for [obese children] to be
successful in school,” says Davidson. “It’s not huge, and maybe
they can overcome it by working harder. But the memory and
cognitive functions in kids [that are affected] are not just about
academics. It’s the way the brain processes information and
Along with attention and memory, executive function also
relates to controlling impulses, decision-making and delaying
gratification. Overweight children show less inhibitory control
compared with normal-weight children, which may make it
harder for them to say no to unhealthy foods, according to a
study by Sussanne Reyes, PhD, of the University of Santiago,
and colleagues (International Journal of Obesity, 2015).
A lack of inhibition may also hurt children in the classroom.
A study by Keita Kamijo, PhD, and colleagues at the University
of Illinois Urbana-Champaign of 128 7- to 9-year-old children
found that compared with normal-weight children, kids with
higher BMIs and fat levels performed worse on tasks that
required inhibitory control and tended to have lower academic
scores (Obesity, 2012).
That reduced ability to
resist gratification, especially
in the form of tasty high-calorie treats, helps explain
why overweight children
are more likely to overeat,
even when they’re not
hungry, researchers say.
Obese children are also more
sensitive to food cues. They
may, for example, be more
likely than normal-weight
children to remember the
chocolate cake in the fridge,
or linger over food at a party,
A brain under siege
Scientists are trying to figure out what causes the damage.
Davidson and colleagues have found in animal studies that
the large amounts of processed sugars and saturated fat in the
Western diet can weaken the blood-brain barrier, especially in
the hippocampus. This makes the brain more vulnerable to
harmful substances that can impair its function, especially as
the hippocampus is a region critical to memory and executive
function. A leaky blood-brain barrier can also affect hippocampal
levels of brain-derived neurotrophic factor (BDNF), a protein
that influences appetite, executive functions and decision-making, and is important to neuron development and long-term
memory, Davidson’s research shows. While research is needed, he
hypothesizes that obesity also weakens the blood-brain barrier in
children and adolescents.
In one study focusing on the relationship between diet and
brain effects, Sara Hargrave, PhD, who works with Davidson,
fed rats a Western diet. Not all rats became obese on the diet,
but those that did performed worse on hippocampal-based
spatial memory tasks than those that were fed low-fat lab chow,
and these obese rats showed evidence of leakage in their blood-brain barrier. Rats fed a high-fat, low-sugar diet did not show
these effects (Behavioral Neuroscience, 2016).
“On its own, body fat isn’t necessarily responsible for these
changes in cognitive performance. But the combination of diets
high in saturated fat and sugar, plus the development of obesity,
seems to create a perfect storm for these deficits,” she says.
APA is sponsoring a panel that is developing an
evidence-based clinical practice guideline for
treatment of obesity in children and adolescents.
A draft of the guideline is expected to be
released by early 2017.
“On its own, body fat isn’t necessarily
responsible for these changes in cognitive
performance. But the combination of diets
high in saturated fat and sugar, plus the
development of obesity, seems to create a
perfect storm for these defifificits.”
Sara Hargrave, PhD
Center for Behavioral Neuroscience at American University