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High-fat diet may be contributing to the increasing diagnosis of ADHD in U.S. children. A new study from University of Illinois has found a significant link between high-fat diet diets and brain conditions that affect learning abilities like ADHD.

Attention deficit hyperactivity disorder (ADHD) is one of the most common childhood disorders and is characterized by a reduced ability in paying attention, difficulty in controlling behavior, and hyperactivity (over-activity), according to the National Institute of Mental Health.

According to data from the Centers for Disease Control and Prevention, more than 5 million American children between ages 3 and 17 have received a diagnosis for ADHD. Recent reports have shown that ADHD is increasing among U.S. children, especially African-American girls.

In the present study, researchers led by Gregory Freund from the U of I College of Medicine, assessed the effects of high-fat diet on mice behavior. The study included two groups of mice, of which one was fed with a high-fat diet with 60 percent fat, and the other with low-fat diet with fat provided 10 percent of the calories.

"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 and a member of the university's Division of Nutritional Sciences.

Researchers noticed that the mice fed with high-fat diet were more likely to increase burrowing and wheel-running and were reluctant to explore open spaces. Also, mice had impaired learning ability. Surprisingly, these behavioral changes occurred even before any noticeable weight gain.

"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 added, according to a news release.

When a few mice from the high fat group were given low-fat diet, their brain activity returned to normal, researchers found. However, in mice that continued high-fat diet, learning remained impaired and they started gaining more weight. Freund said that it takes about 10 weeks for the body to recognize the fat in the diet and adjust brain chemicals accordingly. By this time, the dopamine levels in the brain return to normal.

"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.

Although researchers expected to see evidence of inflammation in the brain of mice fed with high-fat diet, they found that this type of diet actually affects the brain chemistry like addictive substances do, which is by increasing the levels of dopamine.

The study is published in Psychoneuroendocrinology.