Senior author, Gregory Freund, said:
"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."
Altered dopamine signaling is common in both obese/overweight children as well as those with ADHD, Freund explained. When the number of dopamine metabolites is higher, anxiety behaviors in children are more prevalent, he added.
Freund and team were intrigued by the recent increase in childhood obesity prevalence, which appears to have risen in parallel to the number of children with adverse psychological conditions, including ADHD, depression and impulsivity.
Freund and colleagues set out to determine what the effects of a high-fat diet versus a low-fat one might be on the behavior of four-week-old mice. In the high-fat diet, 60% of the calories came from fat, while in the low fat one only 10% came from fat. Typical diets in Western Europe, North America, and Australasia contain between 35% to 45% fat.
The researchers noticed a marked difference in the behavior of the mice in the high-fat diet within a week, even before they were able to detect any weight gain.
The high-fat diet mice started burrowing and wheel running more frequently. They also became more and more reluctant to explore open spaces. Certain memory and learning deficits became noticeable among the mice on the high-fat diet - their ability to negotiate a maze started to deteriorate; their ability to recognize objects also got worse.
The mice on the high-fat diet were then switched to a low-fat one. Even though impaired recognition continued among those that remained on the high-fat diet, the researchers explained that previous studies had shown that the brain biochemistry of mice starts to normalize after about ten weeks as the body begins to compensate for the high-fat diet. Dopamine eventually returns to normal and the mice get fatter and fatter, become obese and develop diabetes.
Is the Western pattern diet triggering anxious behaviors and learning deficiencies in children?
"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."
If mice adapt to a high-fat diet, would an abrupt change to a low-fat one have a negative effect on memory, learning and anxiety, the scientists wondered.
No inflammation - the authors were surprised to find no evidence of inflammatory response in the brains of the mice after three weeks on the high-fat diet. One would expect a high-fat diet to stimulate inflammation.
Instead, there was evidence that a high-fat diet triggers chemical responses similar to ones observed in addiction, with dopamine, the neurotransmitter that drives an addict's pleasurable experiences, rising in the brain.
A different study, carried out by researchers from Duke University Medical Center in Durham, North Carolina, and published in the International Journal of Obesity, found that children with symptoms of ADHD are more likely to become obese adults.
Researchers from Perth's Telethon Institute for Child Health Research found that a diet high in total fat, saturated fat, refined sugar and sodium - a Western diet - is more likely to cause ADHD in adolescents, compared to non-Western diets. Their study was published in the Journal of Attention Disorders (July 2010 issue).
Team leader, Associate Professor Wendy Oddy, said "We found a diet high in the Western pattern of foods was associated with more than double the risk of having an ADHD diagnosis compared with a diet low in the Western pattern, after adjusting for numerous other social and family influences."
Written by Christian Nordqvist