Currently, I am on day 5 of a 7-day fasting regimen, which has led me to question the impact of fasting on the brain and its cognitive performance. It is well known that fasting promotes cellular repair processes such as autophagy, but in this case, I want to focus primarily on cognitive abilities. We have already discussed the influence of diet on brain performance several times, so it seems logical that the absence of food intake would also have a significant, or perhaps even greater, effect.
The State of Research:
Several studies have been conducted on animals, particularly mice, although most appear to have followed an intermittent fasting (IF) protocol.
One study on mice, which divided them into a normally fed group, a group with a 10% calorie reduction, and an IF group, found that the mice in the IF group showed a significantly improved long-term memory. Other studies suggest that fasting triggers neuronal stimulation at the end of the fasting period, meaning that nerve cells transition from a conservation state to a growth state, leading to neuroplasticity. This process, which allows the brain to restructure itself, is what enables children to learn quickly but tends to decline with age. In this regard, incorporating short fasting periods, such as the 5:2 diet, seems beneficial to harness the cognitive effects of breaking a fast.
Even calorie restriction alone, based on the evaluation of numerous studies, already has a very positive effect on the speed of processing new information and short-term memory. However, there are also negative effects: cognitive flexibility, the ability to adapt to changing conditions, decreases. Cognitive flexibility helps us adjust to new situations, find alternatives, and think creatively—such as when you have to change your driving route due to a road closure.
Additionally, fasting has a negative impact on psychomotor skills, which involve coordination between the brain and muscles. This includes simple hand-eye coordination tasks like typing on a keyboard, as well as complex movements such as playing a musical instrument or engaging in sports.
The findings suggest that the extent of calorie reduction plays a crucial role in cognitive changes. A moderate reduction may be beneficial, whereas a severe restriction could have potential negative effects.
Back to Fasting:
There are very few studies examining memory performance in the context of long-term fasting. However, the studies that do exist have not found any negative cognitive effects. From an evolutionary perspective, this makes sense—humans would hardly have survived if cognitive abilities had collapsed during periods of food scarcity. Bad luck for the mammoth.
The previously mentioned 5:2 diet gained popularity a few years ago through a BBC documentary by the late Michael Mosley. Unfortunately, the full documentary is not available on YouTube, but I did find a short excerpt.
https://www.youtube.com/watch?v=gGHDBIaibok