Body fat and an unhealthy diet may impair brain function and lead to cognitive problems in children.
Some 17 percent of American children are obese, a rate that worries public health officials since obesity is linked to diabetes, hypertension, depression and inflammation in children — all of which can raise the risk of cognitive decline as an older adult.
Now, research suggests that harm to the brain may start earlier for obese children by weakening their attention and memory. Growing evidence suggests that being overweight or obese and having a diet high in sugar and saturated fat may also lead to brain changes that hamper children’s impulse control, making it harder to resist eating.
“A variety of findings indicate that these diets and obesity in midlife increase the risk for late life Alzheimer’s disease or other dementias,” says Terry Davidson, PhD, psychology professor and director of the Center for Behavioral Neuroscience at American University. “Now there’s some evidence that these [brain] pathologies are emerging earlier and may even be a cause of obesity, rather than an effect.”
According to the Centers for Disease Control and Prevention, children are overweight when their BMI is at or above the 85th percentile for others of the same age and sex. Obesity is defined as a BMI at or above the 95th percentile.
Excess weight in children is associated with a range of impairments in executive function, including weaker working memory, attention, mental flexibility and decision-making, according to a review by June Liang, PhD, of the Center for Healthy Eating and Activity Research at the University of California, San Diego (UCSD), and colleagues (International Journal of Obesity, 2014). Brain imaging studies have shown structural changes, too. Research by Antonio Convit, MD, of New York University, found that obesity and metabolic syndrome — a combination of weight-related issues such as high blood pressure or triglycerides, insulin resistance, low HDL (good) cholesterol and a big belly — are related to lower academic scores, thinner orbitofrontal and anterior cingulate cortices, less white matter integrity and reduced hippocampal volume (Obesity, 2014).
Psychologists are among those trying to determine how much of these effects are due to diet versus weight. In a study of 52 children ages 7 to 9, University of Illinois Urbana-Champaign researchers found that the children who ate more saturated fats did worse on hippocampus-related item and relational memory tasks — the ability to discern and remember co-relationships among things and ideas — regardless of their 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 remembers things.”
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, Liang says.
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.
An important question, then, is whether this damage can be reversed. To find out, scientists are examining behavioral interventions, such as training children to overcome impulsive eating behaviors. For example, Liang and her mentor Kerri Boutelle, PhD, of UCSD are developing computer-based programs in which children see pictures of both highly palatable foods — rich in sugar, fat and salt — and non-food items, and are asked to inhibit their responses to the pictures of food by pressing a “no” key to indicate they would like to avoid it. Studies suggest that practicing inhibition can strengthen the ability to resist unhealthy foods. Adults in a U.K. study on inhibition training showed significant weight loss compared with controls (Appetite, 2015).
Family-based cognitive behavioral programs can also be effective. Parents can best help their children avoid poor food choices when they are warmly supportive versus being too controlling or using shame or guilt tactics, which Liang’s research shows can lead to an obese child eating more candy (Appetite, 2016).
“Parents need to act as the child’s frontal lobe until it develops — praising them for making the right choices, using portion control, and changing the food environment so there are fewer temptations around,” Liang says.
Teaching mindfulness practices to children may also help prevent obesity, according to Vanderbilt University researchers. In a study of 38 children who had MRI scans, the scientists found that the heavier children who ate more had stronger connectivity among brain areas related to being impulsive, while those who ate less had greater connectivity in areas that promote inhibition. Teaching children mindfulness practices, which research suggests reduces impulsive behavior, might help children maintain a healthy weight (Heliyon, 2016).
Research also suggests that exercise, especially aerobic fitness, may help improve executive function in overweight children. A study of 55 overweight children in a rigorous six-week daily exercise program found that they had better emotional control and visuospatial performance than overweight children who exercised only once a week (Obesity, 2015).
Still, building these interventions into children’s lives is a challenge, says Davidson. “It may not be any easier to get kids to exercise than it is to get them to stop eating ice cream. …We have to make it easier to do.”
Lu, S. (2016, June 1). Obesity and the growing brain. Monitor on Psychology, 47(6). https://www.apa.org/monitor/2016/06/obesity-brain