Brain glucose extraction is fixed at 10% despite twofold variability in resting cerebral blood flow in healthy humans

This commentary addresses the interpretation by Drs. Nybo and Rasmussen of our recent short report examining the interindividual variability in resting human cerebral blood flow (CBF) and metabolism in 75 otherwise healthy adult volunteers. We contend that the authors have mischaracterized the primary objective of the original short report. The objective was to quantify interindividual variability in resting CBF with oxygen and glucose extraction under resting, unstimulated conditions, rather than intraindividual regulatory responses to acute interventions. We highlight that their considerations raised do not invalidate the principal conclusion that lower resting CBF is associated with reduced aerobic glycolysis, possibly due to a greater compensatory capacity of oxygen relative to glucose extraction.