Brain metabolism during fasting.
Level 4 - case-series / case-control
Small physiological case series (n=3) without a control group.
PubMed 6061736 · doi:10.1172/JCI105650
What was done
Cerebral vessel catheterization was performed on three obese patients undergoing 5 to 6 weeks of starvation to evaluate substrate utilization and respiratory quotient in brain metabolism.
What was found
Beta-hydroxybutyrate and acetoacetate replaced glucose as the primary fuel source for cerebral metabolism. A strikingly low cerebral respiratory quotient was also noted, though no numerical values or confidence intervals were provided in the abstract.
Why it matters
This demonstrated that the human brain can adapt to prolonged fasting by shifting its primary metabolic substrate from glucose to ketone bodies.
Limits
The study is restricted to a very small sample size (n=3) consisting entirely of obese individuals undergoing extended starvation. The abstract reports no baseline control data, statistical metrics, or exact quantitative values.
Cited by
- supports Ketones can supply approximately 70% to 75% of the brain's energy requirements, with the remaining 25% to 30% requiring glucose.