Childhood obesity and brain-based conditions in children like learning disabilities and attention deficit hyperactivity disorder (ADHD) may be linked, according to new research released by the University of Illinois on Feb. 19, 2013.
Scientists were intrigued the recent upsurge in childhood psychological conditions and obesity, so they studied the effects of a high- fat diet on four-week-old mice. Researchers measured changes in the levels of dopamine, a pleasure-enhancing chemical in the brain.
“We found that a high-fat diet rapidly affected dopamine metabolism in the brains of juvenile mice, triggering anxious behaviors and learning deficiencies. Interestingly, when methylphenidate (Ritalin) was administered, the learning and memory problems went away,” said Gregory Freund, a professor in the U of I College of Medicine.
Freund said that altered dopamine signaling in the brain is common in children with ADHD and children who are overweight. “An increase in the number of dopamine metabolites is associated with anxiety behaviors in children,” he added.
The study examined the short term effects of a high-fat (60 percent of calories from fat) in comparison to a low-fat (10 percent of calories from fat) diet on two groups of mice. A typical Western diet has 35 to 45 percent fat, Freund said.
“After only one week of the high-fat diet, even before we were able to see any weight gain, the behavior of the mice in the first group began to change,” he said.
The mice on a high-fat showed evidence of anxiety, and learning and memory deficits such as:
- Increased burrowing and wheel running
- Reluctance to explore open spaces
- Decreased ability to navigate through a maze
- Impaired ability to recognize objects
Switching mice from a high-fat to a low-fat diet restored memory in one week, Freund observed. In the mice on a high-fat diet, the mice continued to have impaired object recognition there weeks after the symptoms began.
Other studies have showed that the brain biochemistry normalizes after 10 weeks, which may indicate that the body is compensating for the diet. At that time, the brain’s dopamine levels return to normal, and the mice became obese and diabetic.
“Although the mice grow out of these anxious behaviors and learning deficiencies, the study suggests to me that a high-fat diet could trigger anxiety and memory disorders in a child who is genetically or environmentally susceptible to them,” he said. The researchers speculated that after the animals adapted to the high-fat diet, the removal of fat from the diet might have a negative impact on learning, memory, anxiety, and learning.
Researchers expected that the high-fat diet would stimulate the inflammation in the brain that is connected to obesity after one or three weeks, but found no evidence of swelling. Instead, researchers say that a high-fat diet started chemical reactions in the brain because of an increase in dopamine levels.
The research was published as “Methylphenidate prevents high-fat diet (HFD)-induced learning/memory impairment in juvenile mice” in "Psychoneuroendocrinology" and is available online.