New results from the largest long-term study of brain development and children's health are raising provocative questions about a link between obesity and brain function.
Does excess body weight somehow reduce regions in the brain that regulate planning and impulse control? Is obesity a result of that brain difference? Or are eating habits, lifestyle, family circumstances and genetics to blame?
Previous studies in children and adults have produced conflicting results. And the new research, which appears this week in the journal JAMA Pediatrics, doesn't settle the matter either. Indeed, experts cautioned that the results could unfairly perpetuate weight stigma.
But an editorial published with the study called it an important addition to mounting evidence of a link between weight, brain structure and mental function.
If follow-up research confirms the findings, it could lead to new ways to prevent obesity by targeting improved brain function.
“We don't know which direction these relationships go, nor do they suggest that people with obesity are not as smart as people at a healthy weight,”said Dr. Eliana Perrin, a professor of pediatrics at Duke University and co-author of the editorial.
The federally funded study involved 3,190 U.S. children aged 9 and 10. Researchers measured their height and weight, which allowed them to determine their body mass index. Nearly 1,000 kids — almost 1 in 3 — had a BMI that classified them as overweight or obese, similar to national statistics.
All of the children had MRI brain scans and took computer-based tests to assess mental functions such as memory, language, reasoning and impulse control.
The MRIs of the heaviest children revealed slightly less volume in the brain region behind the forehead that controls what are known as “executive function” tasks. They include things like ability to plan, control impulses and handle multiple tasks simultaneously.
The differences compared with normal-weight kids were subtle, said study author Scott Mackey, a neuroscientist at the University of Vermont.
The heaviest kids also had slightly worse scores on computer-based tests of executive function. But Mackey and study leader Jennifer Laurent, an obesity researcher at the University of Vermont, said it's unknown whether any of the differences had any meaningful effect on children's academic functioning or behavior.
在通过计算机考试的执行功能测试中，体重最重的孩子得分也略差。 但是，麦克基和研究负责人——来自佛蒙特大学的肥胖研究员珍妮弗·洛朗（Jennifer Laurent）表示，尚不清楚这些差异对儿童的学术功能或行为是否产生了有意义的影响。
It's also unclear exactly how these differences are related to weight. It's likely other factors not measured in the study — including physical activity and healthy nutrition — play a far greater role, Mackey said.
Research in adults has linked obesity with low-level inflammation throughout the body, which can damage blood vessels and may increase risks for heart disease and mental decline. Some studies have also found less brain volume in obese adults, and researchers theorize that it could be due to inflammation.
The new study raises the possibility that inflammatory changes affecting weight, brain structure and function begin in childhood.
Still, the results leave many questions unanswered, said Marci Gluck, a research psychologist at the National Institute of Diabetes and Digestive and Kidney Diseases, who was not part of the research.
“Executive function deficits and ‘intelligence' are not the same,” Gluck said.
Natasha Schvey, an obesity researcher at the Uniformed Services University of the Health Sciences in Bethesda, Md., called the study impressive. But she noted that eating habits and obesity are influenced by many factors, including metabolic and psychological differences.
娜塔莎·施维（Natasha Schvey）是马里兰州贝塞斯达市健康科学统一服务大学的肥胖症研究员，她认为这项研究令人印象深刻。 但她指出，饮食习惯和肥胖受许多因素影响，包括新陈代谢差异和心理差异。
“We know from a lot of really good research that obesity is not as much in an individual's control as we think it is,” she said.
“People talk about willpower — that's a very small part of the equation. There are much bigger contributors to our weight and a lot of it is genetic. That's not to say it's immutable.”