Brain Over Breakfast: Investigating the Mental Impacts of Brief Fasting

The next occasion you skip breakfast, you need not fret that your brain will be sluggish. A comprehensive new meta-analysis from the University of Auckland and the Paris Lodron University of Salzburg reveals that brief fasting has minimal to no influence on the cognitive performance of healthy adults. The findings, published in Psychological Bulletin, aggregated data from 71 studies involving over 3,400 individuals to assess whether food deprivation interferes with mental faculties.

Study Outcomes

Through numerous standardized assessments gauging attention, memory, judgment, and inhibitory control, those who had not consumed food performed nearly equivalently to their fed counterparts. The average duration of fasting was around 12 hours, similar to an overnight fast. By employing a hierarchical Bayesian approach, the researchers observed an average effect size near zero (g = 0.02), indicating no significant disparity in cognitive scores between those who were hungry and those who were fed.

“Our primary conclusion was that there’s generally no reliable evidence that brief fasting hampers cognitive performance,” stated David Moreau, PhD, associate professor of psychology at the University of Auckland and the principal investigator of the study. “Those who fasted demonstrated remarkably similar performance to those who had recently eaten, indicating cognitive abilities stay consistent in the absence of food.”

This stability persisted across different domains. Whether recalling lists of words, reacting to visual symbols, or making quick decisions, performance showed minimal variation. Some slight effects were only noticeable when fasting surpassed a full day, and even then, the declines were minimal. Age was a more significant factor. Children exhibited marked decreases in task precision when hungry, confirming previous research that breakfast aids learning and attention in developing minds.

Nevertheless, fasting appeared significant only in specific contexts. When test materials incorporated food-related images or terminology, hungry participants displayed slight distraction effects. Conversely, neutral tests involving numbers or geometric shapes revealed no disparities. This trend implies that hunger sharpens focus on food cues rather than diminishing overall cognitive function.

A Comforting Insight

Brief fasting triggers physiological processes that transition the body from glucose to fat-derived energy known as ketones. These molecules, well-recognized for sustaining human metabolism during periods of scarcity, may also confer protective or restorative benefits. The authors suggest that the brain’s capacity to utilize ketones clarifies why skipping a meal seldom impairs mental acuity.

“The key takeaway is a message of reassurance: Cognitive functioning remains stable during brief fasting, indicating that most healthy adults need not be concerned about short-term fasting affecting their mental clarity or everyday performance,” Moreau explained.

However, extended fasts present a different scenario. The meta-analysis indicated slight declines as fasting durations exceeded 24 hours, especially later in the day when natural circadian declines in glucose occur. Nonetheless, performance generally recovered as participants metabolically adjusted to ketosis. This adaptability reflects what the authors describe as an evolutionary safeguard: humans evolved the ability to think clearly even in states of hunger.

For individuals delving into intermittent fasting, the findings provide scientific reassurance. Short, structured fasting periods seem to be safe for cognitive function and may even align with metabolic advantages such as enhanced insulin sensitivity and cellular repair. The researchers caution, however, that fasting protocols should be meticulously tailored for children or anyone with medical issues.

Psychological Bulletin: 10.1037/bul0000492