After consuming a high-fat diet, juvenile mice became more anxious and experienced learning difficulties, according to a study published last week in the journal Psychoneuroendocrinology. The authors of the February 2013 paper claim that when taken with other recent research, the experiment is evidence of a possible link between childhood obesity and attention deficit hyperactivity disorder (ADHD).
Researchers from the University of Illinois compared the behavior and brain chemistry of mice fed a diet containing 60 percent calories from fat with that of mice fed a diet with 10 percent calories from fat. They observed that the mice on high-fat diets burrowed and ran on an exercise wheel more than other mice, and were more reluctant to explore open-spaces — traits that the researchers said were proof of anxiety. The mice on high-fat diets were also less able to navigate mazes and recognize objects, indicating impairments in learning and memory.
When the researchers examined the brain chemistry of the mice, they found that the neurotransmitter dopamine increased during the first couple of weeks of the high-fat diet, but then returned to normal levels. Dopamine is involved in regulating the brain’s reward system, and lower levels of dopamine have been linked to the pleasure-seeking behavior common in addiction.
The authors suggest their mouse-model is consistent with past research indicating that insensitivity to dopamine contributes to poor impulse-control in children with ADHD. In addition to high fat intake, other studies have implicated another contributing factor to obesity – sedentary lifestyle – in the planning deficiencies associated with ADHD.
Mice are not children, however, and it is unclear how much the University of Illinois research generalizes to humans. The researchers note in their paper that burrowing and wheel running are not universally accepted measures of anxiety in mice, and so their interpretation of the results is debatable.
While the researchers found that Ritalin, a drug commonly used to treat ADHD in children, also alleviated the mice’s problems with learning and memory, it is possible that ADHD and obesity are two distinct problems marked by similar irregularities in brain chemistry. Any attempt to tie the rise of childhood obesity to a perceived increase in ADHD could be mistaking correlation for causation, and should be taken with a grain of salt until the research bears out.