Skipping breakfast is often associated with “brain fog,” irritability, and reduced productivity. However, the popularity of intermittent fasting has grown sharply in recent years, with millions of people using it to manage weight and improve metabolism. This raises an important question: is it possible to gain metabolic benefits without harming cognitive abilities? An international group of researchers conducted the largest meta-analysis to date to examine how fasting affects brain function, according to The Conversation.

Scientists analyzed 63 scientific publications, including 71 independent studies involving 3,484 participants. In total, 222 indicators of cognitive performance were evaluated, including attention, memory, and executive functions. The studies covered nearly 70 years of research, from 1958 to 2025.

The main conclusion was unexpectedly reassuring: among healthy adults, no significant differences in cognitive performance were found between fasting and fed states. Participants performed memory and concentration tests at roughly the same level regardless of whether they had recently eaten.

The authors explained this through what is known as “metabolic switching.” About 12 hours after eating, glycogen stores become depleted, and the body begins using ketone bodies — an alternative energy source produced during fat breakdown. These compounds can efficiently supply the brain with fuel, compensating for reduced glucose levels.

However, the study identified several important nuances. Age proved to be a key factor. No decline in cognitive performance was observed in adults, but cognitive results worsened in children and adolescents when meals were skipped. The authors emphasize that the developing brain is more sensitive to fluctuations in energy supply, meaning regular meals remain important for school-age individuals.

A second factor was time of day. Participants tested later in the afternoon showed greater fluctuations in performance while fasting. Researchers suggest that hunger may amplify natural circadian dips in alertness.

The researchers conclude that, for most healthy adults, intermittent fasting is not associated with impaired mental performance. However, it is not a universal strategy: children, adolescents, and individuals with certain medical conditions should consult a physician before experimenting with dietary regimens.