The impact of the 5:2 intermittent fasting diet on cognition in healthy adults

Objectives: Research suggests that a reduction in calories may impact cognitive functioning in healthy adults. Despite studies that demonstrate changes to cognitive function following periods of fasting and continuous calorie restriction, any potential impact for those who follow intermittent fasting (IF) diets remains unclear. Among the most popular IF diet is the 5:2 fasting diet. Proponents of this dieting regime claims that it has numerous benefits to general health. Less in known about the impact of this diet on cognition. Given that some studies have shown cognition is impaired following acute fasting, concerns remain about the impact of a fasting diet that encourages high levels of intermittent calorie restriction. This study sought to understand the impact on specific areas of cognition for healthy adults who follow the 5:2 diet. Methods: Part A Using a within-subjects repeated measures design, 36 healthy adults who were following the 5:2 diet for more than four weeks were measured for cognitive performance on fasting and non-fasting days using a range of online cognitive tasks. Specifically, we measured cognitive flexibility, working and prospective memory, reflective impulsivity and psycho-motor speed. Part B Using a between-subjects design, mean performance on the cognitive tasks for healthy adults following the 5:2 diet (n=36), was compared to those following CCR diets (n=30). Both groups had been following their diets for more than four weeks. Results: Part A Cognitive flexibility, working and prospective memory was impaired on fasting days along with a reduction in impulsivity. Overall composite scores revealed impaired reaction time and accuracy on fasting days. Part B Participants following the 5:2 diet performed worse than those following CCR diets in tasks designed to measure psycho-motor speed and cognitive. Overall composite scores revealed impaired reaction time for those following 5:2 diets, compared with those following CCR diets. Conclusions Research that investigates the impact of calorie restriction and fasting on cognitive function should also consider the potential risks of cognitive impairment for those who choose to follow intermittent fasting diets. Future studies would benefit from longer term measurement of cognition for those following IF diets whilst accounting for potential confounding variables