Cognitive Performance Deficits of Dieters

Abstract

The present chapter reviews the literature concerning the psychological effects of one of the most commonly undertaken food choice-related behaviors in the Developed World– caloric restriction via weight loss dieting. The severe chronic caloric restriction associated with anorexic psychopathology is associated with a range of neuropsychological impairments resulting from starvation-related alterations in brain anatomy and chemistry. Severe, chronic nonpsychopathological caloric restriction has also been associated with a range of impairments in cognitive function and mood. The degree of caloric restriction characteristic of weight loss dieting has, however, been less reliably associated with impaired psychological function, the phenomenon being dependant on the manner in which weight loss is attempted, the degree of weight loss, and the precise nature of the psychological assessment battery. In general, the evidence concerning the effects of controlled, laboratory-based caloric restriction is mixed, with some studies showing no effects of laboratory-induced caloric restriction, some showing a negative psychological impact of restriction, and some actually showing an improvement in certain psychological domains (recognition memory). Methodological issues surrounding this phenomenon are discussed. In contrast, spontaneously undertaken weight loss is reliably associated with impairments in the performance of a range of cognitive performance measures. Primarily, the cognitive deficit associated with spontaneous dieting appears to be a reduction in available working memory capacity, this being the cognitive system which allocates limited cognitive resources to other, ongoing activities and remembering the moment-to-moment rules of action. This reduction results from dieting-related preoccupying cognitions concerning body shape, hunger, and food which preferentially consume the limited amount of working memory capacity. Support for this, rather than a biological explanation, can be seen in the findings that the cognitive impairments are most marked during the early stages of attempted weight loss and are independent of the degree of weight actually lost over the course of the diet.

The present chapter also examines a number of possible alterations in biochemical status to account for the impairment in psychological function associated with spontaneous dieting. These include compromised iron metabolism and serotonergic function. Whilst these factors undoubtedly do affect psychological function, the evidence for their role in impairing the cognitive function of dieters is not compelling. Rather, the negative psychological impact of dieting on cognition appears to be related to the stress of attempted weight loss. This is borne out by the finding that impaired cognitive function is not observed in individuals who diet as part of a supported, organized diet group and that the working memory capacity of unsupported dieters is related to salivary cortico-steroid secretion.