New review of 63 articles finds short-term fasting doesn’t harm cognitive performance

Fasting can be an effective strategy for losing weight, yet many people assume that going without food must come at the cost of brainpower.

So is a drop in cognitive performance simply part and parcel of fasting?

A large, recently published review suggests that it is not necessarily so.

Drawing on 63 scientific articles that covered 71 independent studies and a combined 3,484 participants, the authors reported no meaningful difference in cognitive performance between people who were fasting and those eating normally.

The findings push back against the widespread notion that moderate, short-term limits on eating will drain mental energy in otherwise healthy people-an idea reinforced by everything from snack advertising (“you’re not you when you’re hungry”) to the common refrain that breakfast is the most important meal of the day.

The researchers-psychologist Christoph Bamberg of Paris Lodron University in Austria and cognitive neuroscientist David Moreau of the University of Auckland in New Zealand-say people who might benefit from fasting should not be deterred by fears of muddled thinking.

"For most healthy adults, the findings offer reassurance," Moreau explained in a commentary for The Conversation.

"You can explore intermittent fasting or other fasting protocols without worrying that your mental sharpness will vanish."

What the review says about fasting and cognitive performance

Across the included studies, researchers measured a range of cognitive skills, such as memory recall, decision-making, and the speed and accuracy of responses.

When results were considered together, short-term fasting-typically around a median duration of 12 hours-did not materially shift performance scores.

In other words, for most healthy adults, briefly abstaining from food did not appear to reduce overall mental performance compared with having regular meals.

When fasting may affect thinking

The review also highlighted important nuances.

The authors observed modest reductions in cognitive performance when fasting periods extended beyond 12 hours, alongside "noticeable declines" among children and teenagers (although young people represented only a small share of participants).

This pattern implies that developing brains may be more vulnerable to extended periods without food, and that for children and adolescents, three regular meals each day remains particularly important.

The clearest effects tended to show up in tasks linked to food. That raises the possibility that certain brain systems may become more strained during fasting, although the researchers note that more work is needed to confirm this.

"Performance deficits were often evident only in tasks involving food-related stimuli, such as looking at pictures of food or processing food-related words," Moreau said.

"In contrast, performance on tasks using neutral content was largely unaffected."

"Hunger might selectively divert cognitive resources or cause distraction only in food-relevant contexts, but general cognitive functioning remains largely stable."

The analysis also found that fasting participants were more likely to score worse on cognitive tests conducted later in the day. One interpretation is that not eating may amplify the normal ebb and flow in alertness linked to circadian rhythms.

Fasting, metabolism and practical guidance

Beyond supporting weight management for some people, fasting has been linked in scientific research to other potential health benefits, including improved cardiovascular health and lower inflammation.

Scientists also believe fasting can trigger substantial shifts in how the body fuels itself, including a move away from using stored glycogen towards relying more on body fat-particularly through molecules known as ketone bodies.

With that context, Moreau argues that "fasting is best seen as a personal tool rather than a universal prescription".

There is no single approach that suits everyone, and fasting is best undertaken in consultation with a medical professional.

"The primary takeaway is a message of reassurance: Cognitive performance remains stable during short-term fasting, suggesting that most healthy adults need not worry about temporary fasting affecting their mental sharpness or ability to perform daily tasks," Moreau said.

The research was published in Psychological Bulletin.