Analysis included 63 studies and 3,484 participants.

Pooled standardized mean difference = 0.02 (no cognitive change).

Fasting durations ranged 3–336 hours (median 12 hours).

Shorter fasts (< 48 hours) showed 0.01 unit smaller gap per extra hour.

Slight decrements appeared only in food-related cognitive tasks.

Attention, working memory, and executive function remained stable.

Study funded by Royal Society of New Zealand Marsden Fund and University of Auckland.