Nutrition Research Newsletter: Decision-making deficits and overeating

Data from a number of reliable sources suggest that the pattern of population weight gain over the past generation has been due largely to an overconsumption of energy rather than a decrease in physical activity patterns. However, the fattening of the society goes well beyond esthetic issues; 300,000 people in the United States alone die each year of obesity-related illnesses, and this condition affects more people than smoking, heavy drinking, and poverty. More sobering is the prediction that, if current trends continue, 100% of Americans will be obese by the year 2230. The evidence of common brain mechanisms mediating the rewarding properties of natural rewards (such as eating) and addictive drugs supports the argument that food--especially when it is highly palatable--can be used for purposes that exceed basic energy requirements, and it has the potential for abuse. For instance, many people report using food to "self-medicate" a disturbed affect. Of relevance is research showing that sweet foods, such as certain addictive drugs, can produce significant analgesic effects. Excessive food intake can also induce physiological responses that mimic those seen in drug addiction.

The ventromedial prefrontal cortex (VmPFC) has been strongly implicated in a neural system, including the amygdala-ventral striatum, that is necessary for making advantageous decisions when various options are available for action. In particular, its critical function in this process is to activate feelings or emotional states from "thoughts" about rewarding or punishing events that are not currently present in one's immediate environment. Much of the early research on decision making came from studying the deficits of patients with VmPFC lesions and learning that their impairment reflects an inability to advantageously assess future consequences, both positive and negative, so that their behavior is always guided by the immediate contingency. Given the behavioral similarities between patients with VmPFC lesions and drug abusers (both make choices that bring immediate benefit despite long-term negative consequences), recent studies have investigated VmPFC function in drug addicts using a "gambling task," which has demonstrated sensitivity in detecting the decision-making impairment of the VmPFC patients. Results have consistently demonstrated that many addicts show decision-making deficits.

The present research extended these findings to the study of overeating and obesity. As part of ongoing behavior genetics research at the Centre for Addiction and Mental Health in Toronto, Canada, 41 healthy adult women (mean age = 28.5 years) participated in this study. Emotional overeating was assessed by the Emotional Eating Scale. Decision making was assessed by the computerized version of the Iowa Gambling Task. Subjects had to choose among four decks of cards presented on a computer screen, two of which (A and B) yielded high immediate gain (but larger future losses), and two of which (C and D) yielded lower immediate gain but a smaller future loss. The subjects were informed that the goal of the game was to accumulate as much (play) money as possible by picking one card at a time from any of the four decks across 100 trials.

Results from this study provided support for the hypothesis that poor decision making, as assessed by the gambling task, tends to characterize those who are overweight and obese. Indeed, as a group, the high BMI subjects showed greater performance impairments than the substance-dependent patients in the study by Bechara and Damasio. The results of the present study also showed, similar to other research, that self-reports of overeating during periods of negative mood were significantly related to higher BMI. However, there was little support for the proposal that poor decision making contributes to an increase in BMI by fostering overeating during periods of negative emotion. Other means should be considered whereby poor decision making may lead to increased BMI. It is also important to acknowledge that although there is an implied directional relationship between emotional overeating and BMI, by proposing that the former influences the latter, it is entirely possible that the relationship is bidirectional. An increased BMI could lead to more frequent periods of depressed mood and, therefore, more overeating.

C Davis, R Levitan, P Muglia, C Bewell, J Kennedy. Decision-making deficits and overeating." A risk model for obesity. Obes Res 12:929-935 (June 2004) [Correspondence: Caroline Davis, York University, 343 Bethune College, 4700 Keele Street, Toronto, ON M3J1P3, Canada. E-mail: cdavis@yorku.ca]