LONDON, Nov 8: A large review of more than 70 studies has found that short-term fasting has little effect on adult cognitive performance, offering reassurance to millions of people who skip meals for health or weight management.

The research, conducted by experts at Paris Lodron University Salzburg (PLUS) in Austria and the University of Auckland (UA) in New Zealand, shows that adults maintain stable attention, memory, and reasoning abilities after fasting for 8 to 24 hours.

The study was led by Dr. Christoph Bamberg, a cognitive scientist at PLUS, who focuses on how eating patterns and expectations shape attention and memory. Dr. David Moreau, a neuroscientist at UA and the study’s senior author, said, “People often worry that if they fast, they will not be able to concentrate at work or study effectively. Our results show that, for most adults, short-term fasting is unlikely to have a major impact on mental sharpness.”

Across standardized cognitive tasks, adults who had fasted performed similarly to those who had eaten. Small dips in performance were noted later in the day, coinciding with natural circadian declines in alertness, and when tasks included food cues, such as judging portions or reacting to images of food. Neutral tasks were unaffected.

The research highlights the adult brain’s resilience during temporary food shortages. Short fasts trigger a metabolic “fuel switch,” in which the liver converts fat into ketones—energy-rich molecules that substitute for glucose and support neuron function. Ketones also interact with cell signaling linked to stress resistance and efficiency, helping maintain cognitive performance.

Children and teenagers, however, showed a different pattern. A review of school breakfast studies indicated that skipping morning meals can impair attention, memory, and problem-solving in younger learners. Developing brains require more glucose, making them more sensitive to long gaps between meals, particularly before school. Experts recommend breakfast to support learning and mental performance.

Timing and context also play a role. Human cognitive performance follows daily rhythms, peaking during body clock highs and dipping at lows. Fasting can intensify these dips, especially later in the day, and food-related tasks can distract attention. Researchers advise scheduling demanding mental work earlier in the day and breaking fasts before late-day activities to maintain focus.

The review concludes that for healthy adults, skipping a meal is unlikely to compromise everyday thinking, including tasks such as reading, planning, and basic problem solving. Longer fasts may feel more challenging before noon, though objective cognitive performance remains largely unaffected.

Experts caution that people with medical conditions, pregnant individuals, or those with a history of disordered eating should seek personalized guidance. The findings do not apply to multiday fasts, illness, or fasting without water.