Does Fasting Sharpen Thinking

A 2025 meta-analysis of 71 studies and 3,484 participants found that short-term fasting affects cognitive performance by exactly 0.02 standard deviations — statistically indistinguishable from zero. The battery model of willpower, famously proposed in 2007 and claiming glucose fuels self-control, collapsed when 23 labs failed to replicate it. Robert Kurzban's 2010 alternative flipped the script: glucose is an input to decision-making, not a ceiling on capacity. What fasting reliably changes is mood — a 21-day experience sampling study with 9,142 reports found hunger predicts irritability, not impaired thinking.

You'll learn:

- Why the feeling of brain fog doesn't match actual performance data

- How time of day predicts cognition better than fasting duration

- What 1967 ketone research revealed about the brain's backup fuel system