Acute Metabolic and Neurocognitive Adaptations to Short-Term Fasting

Abstract

This study examined the metabolic, cognitive, and electrophysiological adaptations to a 48-hour water-only fast in a cohort of adults (n = 10). Blood glucose, β -hydroxybutyrate (BHB), Trail Making Test A (TMTA) and B (TMTB) performance, and auditory P300 event-related potentials were measured at baseline, 24 hours, and 48 hours. Glucose decreased progressively from 104.5 ± 10.2 mg/dL at baseline to 69.2 ± 7.9 mg/dL at 48 h (−34%), while BHB rose from 0.27 ± 0.15 mmol/L to 2.73 ± 0.81 mmol/L, indicating robust nutritional ketosis. TMTB completion time improved by 22% over the same period (95.4 ± 12.7 s to 73.2 ± 10.8 s), suggesting enhanced executive function during early ketosis. P300 latency and amplitude remained stable across all time points, indicating preserved cortical processing speed and attentional resource allocation. Exploratory sex-stratified analysis revealed greater ketone elevation in males at 48 h (3.64 ± 0.54 mmol/L) versus females (1.99 ± 0.62 mmol/L), without corresponding differences in cognitive or electrophysiological measures. These findings demonstrate that prolonged fasting elicits a predictable metabolic shift toward ketosis without impairing, and potentially improving executive performance, underscoring the need for further research into the cognitive effects of acute nutritional ketosis.