According to the CDC, over 41% of US adults are obese and one in three are overweight, making obesity an epidemic. Now new research shows obesity in childhood negatively impacts brain health, which is concerning considering 20% of American children are obese. "We know being obese as an adult is associated with poor brain health," says researcher Simone Kaltenhauser, a post-graduate research fellow in radiology and biomedical imaging at the Yale School of Medicine in New Haven, Connecticut. "However, previous studies on children have often focused on small, specific study populations or single aspects of brain health."
Using MRI scans, the researchers studied the brain health of 5,169 children, of whom 21% were overweight, and 17.6% were obese. The results? The MRIs of the overweight and obese children showed structural brain changes, especially significant impairment to white matter.
"It is striking that these changes were visible early on during childhood," Kaltenhauser says. Researchers also noticed thinning in the outermost layer of the brain (the cortex). "We expected the decrease in cortical thickness among the higher weight and BMI z-score children, as this was found previously in smaller subsamples of the ABCD study. However, we were surprised by the extent of white matter impairment. Increased BMI and weight are not only associated with physical health consequences but also with brain health. Our study showed that higher weight and BMI z-scores in 9- and 10-year-olds were associated with changes in macrostructures, microstructures, and functional connectivity that worsened brain health."
Studies show that obesity in children is linked to poor school performance and cognitive functioning—but what is causing this epidemic? Here's what experts have to say.
Obesity and Brain Health
Obesity negatively impacts brain health throughout life. "There is pretty robust and substantial evidence that goes across the whole of childhood, from toddlerhood to adolescence, that shows a higher weight status is associated with lower cognitive functioning, particularly in the area of executive function," says Alexis Wood, assistant professor of pediatric nutrition at the Children's Nutrition Research Center at Baylor College of Medicine in Houston. "Why that is, is the subject of much debate."
There is a chicken-and-egg debate over the exact link between obesity and brain health. "If cognitive function challenges come first, the prevailing thought is that this regulates how children interact with their environment," Wood says. "They might not be so good at regulating food intake to balance their energy needs. They might eat when they're not hungry, when they see something very appetizing like a cupcake. Lower cognitive function in this area alters eating behavior and predisposes you to poor eating behaviors."
Am I Obese?
According to the CDC, a BMI of 25.0 to <30 counts as overweight, and 30.0 or higher is obese. "As in adults, obesity is also a growing problem in children and adolescents. Because children grow at different rates, depending on their age and gender, the definitions of overweight and obesity in children and adolescents differ from those in adults," says the Harvard T.H. Chan School of Public Health. "In the US, for example, the definition is based on standard growth charts developed by the Centers for Disease Control and Prevention. In children and adolescents age 2 to 20 years old, a BMI in the 85th to 94th percentiles for age and gender is considered overweight; a BMI in the 95th percentile or higher is considered obese."
Abdominal fat must also be taken into account—excess belly fat (a waist measurement of 35 inches or more for women and 40 inches or more for men) is considered particularly dangerous. "The issue is health, not cosmetics," says Dr. Garth Davis, a bariatric surgeon at Houston Methodist. "The presence of visceral fat is a good predictor of the development of chronic metabolic disease, whether it's hypertension, heart disease or diabetes. The heavier you are, the fuller the standard areas to store fat become, meaning that the fat ends up being deposited around your abdominal organs and your heart. In surgery with these patients, it's a very short distance from the skin to the belly, but then the belly is just filled with fat — fat in the liver, fat lining the intestines, fat everywhere."
The Dangers Of Obesity
Research published in the Journal of the American Medical Association Network Open shows that obesity significantly increases the risk of type 2 diabetes and coronary artery disease, independent of the factors associated with obesity. "This study is important because we can conclude that it is not solely factors like high blood pressure, high cholesterol or lack of exercise that tend to come with obesity that are harmful — the excess fat itself is harmful," explains study senior author and preventive cardiologist Haitham Ahmed, MD. "Patients may think their cardiovascular risk is mitigated if their other risk factors are normal or being treated, but this study suggests you cannot ignore the extra weight. Physicians should take heed and make sure they are counseling their patients about weight loss in a comprehensive and collaborative manner.
"It is very important to recognize that while lifestyle factors certainly contribute to obesity, obesity is not simply a lifestyle choice. It is a disease, and there is large genetic influence on your weight," Dr. Ahmed says. "Our data show that nearly 100 genetic variations influence the development of obesity and subsequently increase your risk of heart disease."
Obesity and COVID-19
Obesity has been shown to be more deadly in people who contract COVID-19, researchers say. One study published in Obesity Reviews showed that obese people who were infected with SARS-CoV-2 were 113% more likely to need a hospital stay compared to those with a healthy BMI. They were also 74% more likely to end up in an ICU—and 48% more likely to die from the virus.
"We didn't understand early on what a major risk factor obesity was. … It's not until more recently that we've realized the devastating impact of obesity, particularly in younger people," says Anne Dixon, a physician-scientist who studies obesity and lung disease at the University of Vermont. "That may be one reason for the devastating impact of COVID-19 in the United States, where 40% of adults are obese."
The #1 Cause of Obesity
The causes of obesity are still very much the subject of debate—in the past, the calories-in-calories-out energy balance model was held as the cause of obesity, but now some scientists are saying this reasoning is flawed and simplistic. "In principle, it sounds simple: eat less and move more," says Dr. David Ludwig, endocrinologist at Boston Children's Hospital and professor at Harvard Medical School. "This dietary advice for tackling obesity has been around for decades. Yet, despite all the calorie counting, dieting and exercising, worldwide obesity rates just keep ticking up. People in the US, for example, were heavier in 2021 than they were in 2020, placing many more people at risk from diabetes and other serious chronic diseases. So why hasn't this approach to weight control worked?"
One factor Dr. Ludwig discusses is the role carbohydrates play. "Processed, rapidly digestible carbohydrates – foods like sweetened breakfast cereals, potato chips and sugary beverages – raise our insulin level too high," he says. "This causes our fat cells to take in and store too many calories, leaving fewer available for the rest of the body. A few hours after eating a high-carb meal, the number of calories in the bloodstream plummets, so we get hungrier sooner after eating. Replacing processed carbs with high-fat foods – such as nuts, full-fat dairy, olive oil, avocado and dark chocolate – lowers insulin levels, making more calories from the meal available for the rest of the body. Counter-intuitively, higher-fat foods may help shed body fat, a possibility supported by clinical trials comparing high-fat diets with low-fat ones."