New research shows obesity may cause mental fatigue

Obesity has been shown to place physical stress on the body, but excess weight may also cause mental fatigue, according to new research published in The FASEB Journal.

For the study, researchers at Southern Illinois University Edwardsville aimed to learn more about the onset of obesity and its impact on both physical and mental abilities by studying two groups of rats. One group was fed a high-fat diet, and the other ate a standard diet for six weeks.

Obesity can increase the risk of high blood glucose, which may develop into type 2 diabetes and other metabolic disorders if untreated. Impaired exercise capacity or physical stamina may also be a problem for people who are overweight. Compromised cognitive function, however, has not been associated as strongly with obesity as physical limitations.

The research team measured the rats' weight, blood glucose and ketone levels twice a week. Ketones are chemicals made by the liver when there is not enough insulin in the body to convert glucose into energy. In the fifth week, the researchers administered an open-field test, which measures speed and distance as the animals move through a maze in each time frame and determines physical exhaustion. A novel object recognition test, which measures mental exhaustion by analyzing the time the rats spend examining new and familiar objects, was given in the final week of the trial.

Both rat groups gained weight during the trial, but the high-fat diet group gained more than the control group. Blood glucose levels fluctuated more in the high-fat diet group as well. There was no significant difference in the average glucose levels or ketones between the two groups.

The high-fat diet group performed poorly on the novel recognition test when compared with the control group.