The Impact of Continuous Calorie Restriction and Fasting on Cognition in Adults without Eating Disorders

Research into the effects of calorie restriction continues to intrigue those interested in whether it may allow humans to live longer and healthier lives. Animal studies of continuous calorie restriction and fasting have demonstrated significant advantages to health and longevity. However, concerns remain over the impact of restricting calorie intake on human health and cognition. Given that there is emerging evidence of cognitive impairments in eating disorders, studies investigating restricted calorie intake in healthy humans may also have implications for understanding restrictive eating disorders (and does so in an ethical way). This review aimed to synthesize the published literature on the impact of continued calorie restriction and fasting on cognitive function in healthy human participants. We identified 33 studies of continued calorie restriction and fasting in humans, with 23 demonstrating significant changes in cognition. Despite variation across the cognitive domains, the results suggest that continued calorie restriction benefits inhibition, processing speed and working memory but may lead to impairments in cognitive flexibility. The results of fasting studies suggest that fasting is associated with impairments in cognitive flexibility and psychomotor abilities. Overall, the results of these studies suggest that the degree (i.e. the severity) of calorie restriction is what most likely predicts cognitive improvements as opposed to impairments. For example, total fasting (where no calories are ingested) is more likely to lead to impairments than modest calorie restriction. For individuals engaging in sustained restriction (in the context of eating disorders, for example), this may have serious, irreversible consequences. However, there are mixed findings regarding the impact of continuous calorie restriction and fasting on this aspect of human functioning, suggesting further research is required to understand the costs and benefits of different types of calorie restriction.