Does fasting or eating less help your memory and concentration?

Skipping breakfast harms your concentration and memory in the short term. A large systematic review (45 studies) in children and teenagers showed that those who eat something in the morning perform measurably better that same morning on attention, working memory and problem-solving than those who remain fasted. The difference was largest in undernourished children. Note: the review was funded by a cereal manufacturer, which may colour the emphasis on breakfast. In university students, skipping breakfast was associated with lower memory scores and poorer academic results, but that was a snapshot study without proof of causation.

For intermittent fasting over the longer term, the picture is more nuanced. In insulin-resistant older adults, 5:2 fasting (eight weeks) improved memory and executive functions, and MRI measurements also showed that the biological ageing rate of the brain decreased. Notably, a healthy diet without fasting performed equally well on most measures; fasting only yielded a little extra gain on specific sub-scores. In postmenopausal women with obesity, fasting alone (two fasting days per week, three months) had no measurable cognitive effect whatsoever. Only the combination of fasting with exercise led to improved executive function and memory.

Animal research points to a mechanism by which fasting raises a brain protein that supports learning and memory. That sounds positive, but the same animal experiments also reveal a warning: in older male mice, fasting disrupted spatial memory and a substance in the brain that regulates signal transmission declined. In older female mice, one type of memory improved while another worsened. In short, fasting does not work equally favourably for everyone in animals, and older age appears to be a risk factor.

What does this mean in practice? Skipping breakfast has a real, if short-lived, detrimental effect on concentration and memory, especially if you are already on the lean side. Long-term fasting as a method of becoming sharper is not sufficiently well supported to count on it. If you want to fast and also want cognitive benefits, the available research suggests that it is best combined with regular exercise. The evidence is still preliminary and the groups studied are relatively small, so firm statements about dosage or the ideal fasting variant cannot yet be made.