Obesity Linked to Changes In Cognitive Patterns

America's obesity epidemic is prompting psychiatric researchers to focus more attention on possible interplays between the psyche and being overweight.

For example, anxiety, depression, binge eating, and night-eating syndrome have been linked with obesity. There is also growing evidence that obesity is related to Alzheimer's disease.

And now a new inquiry has linked obesity with defective executive function. The investigation, which was headed by John Gunstad, Ph.D., an assistant professor of psychology at Kent State University, is in press with Comprehensive Psychiatry.

The study included 408 subjects aged 20 to 82. each had been screened to make sure that he or she was free of medical conditions that had the potential to influence cognitive performance, such as traumatic brain injury, neurological disorder, high blood pressure, cardiac disease, thyroid disease, or sleep apnea.

Gunstad and his colleagues gave the subjects various cognitive tests. The researchers then looked to see whether there were any links between subjects' performances on the cognitive tests and their body mass index.

A statistically significant link was found between subjects' performances on all of the cognitive tests and their body mass index—in other words, body mass index was inversely related to performance on all cognitive tests. Yet, after taking age, gender, IQ, years of education, and other possibly confounding factors into consideration, only impaired executive function significantly differentiated overweight or obese subjects from those of normal weight.

Potentially Important Finding Cited

“I think it's a really interesting and novel study of a potentially important phenomenon,” Michael Devlin, M.D., an associate professor of clinical psychiatry at Columbia University and a binge-eating investigator, told Psychiatric News. “Although the link between overweight/obesity and impaired executive function is relatively weak, it's there, as evidenced by this and other studies.... What is much less clear is the mechanism and... even the directionality of the link.”

Gunstad and his colleagues concurred. As they pointed out in their paper, it is possible that obesity causes impaired executive function since many of the pathophysiological changes associated with obesity—for example, vascular changes, impaired insulin regulation, reduced cardiovascular fitness—could negatively impact executive function. But, they added, it is also possible that persons with a defective executive function are more likely to become overweight or obese since many aspects of executive function—for instance, impulse control, self-monitoring, goal-directed behavior—seem to bear directly on the ability to maintain weight.

A similar question pertains to links that have been made between obesity and various psychological disorders. For example, does obesity lead to depression, or does depression lead to obesity? The only psychological disorder that has been demonstrated to cause obesity, not result from it, is the night-eating syndrome (Psychiatric News, September 16, 2005).

“Additional work is needed to determine the directionality of the relationship between elevated body mass index and executive function,” Gunstad and his team concluded in their report, “particularly prospective studies assessing cognitive performance before and after significant weight loss.”

Cognition and Weight Loss Studied

In fact, Gunstad told Psychiatric News, “We are about to start [such] a longitudinal project to look at cognitive function in persons who undergo bariatric surgery. Patients undergoing those procedures lose a large amount of weight in a relatively short period of time.... This project is being conducted with researchers at Columbia, including Mike Devlin... and at the Neuropsychiatric Research Institute in Fargo, N.D.”

This exploration, Gunstad continued, should not only help answer the question of whether obesity impairs executive function or vice versa, but may well have some practical value.

For instance, “It is possible that persons with deficits in executive functioning... have more difficulty following recommendations from health professionals and aren't as successful at losing weight. If this is the case, neuropsychological screening of patients might identify those likely to have such problems, and weight-loss interventions could be modified to improve the likelihood of success.”

Moreover, “understanding the possible relationship between cognitive function and weight loss might be important in working with older adults who are trying to lose weight. Even healthy older adults show decline in cognitive function, and it is possible that these changes might make it more difficult for some to follow the prescribed intervention.... With the growing number of older adults and the rising prevalence of obesity, weight-loss programs may need to be tailored for older adults to accommodate these concerns.”

This study required no funding. All data were obtained from the Brain Resource International Database at<www.brainnet.org.au>.

An abstract of “Elevated Body Mass Index Is Associated With Executive Dys-function in Otherwise Healthy Adults” can be accessed at<www.sciencedirect.com> by clicking on “Browse A-Z of journals,” then “C,” then “Comprehensive Psychiatry.” ▪