BRAIN METABOLISM DURING SHORT-TERM STARVATION IN HUMANS

During prolonged starvation, brain energy requirements are covered in part by the metabolism of ketone bodies. It is unknown whether short-t erm starvation of a few days' duration may lead to reduced brain gluco se metabolism due to the change toward ketone body consumption. In the present study we measured the cerebral metabolism of glucose and keto ne bodies in nine healthy volunteers before and after 3.5 days of star vation. Regional glucose metabolism was measured by dynamic positron e mission tomography using [F-18]2-fluoro-2-deoxy-D-glucose. The mean va lue of K-1() in gray and white matter increased by 12% (p < 0.05), wh ereas k(2)() and k(3)(*) were unchanged compared with control values. Regional glucose metabolism in cortical gray matter was reduced by 26 % from 0.294 +/- 0.054 to 0.217 +/- 0.040 mu mol g(-1) min(-1) (p < 0. 001). White matter glucose metabolism decreased by 27% (p < 0.02). The decrease was uniform in gray and white matter with regional decreases ranging from 24 to 30%. A determination using Fick's principle confir med the reduction in glucose metabolism yielding a decrease of 24% fro m 0.307 +/- 0.050 to 0.233 +/- 0.073 mu mol g(-1) min(-1) (p < 0.05), whereas CBF did not change (0.57 +/- 0.07 vs. 0.57 +/- 0.06 ml g(-1) m in(-1)). The global net uptake of beta-hydroxybutyrate increased 13-fo ld from 0.012 +/- 0.024 to 0.155 +/- 0.140 mu mol g(-l) min(-1) (p < 0 .05). Net uptake of acetoacetate and net efflux of lactate and pyruvat e did not change significantly during starvation. The present study sh ows that the human brain adapts to the changes in energy supply as ear ly as 3 days following initiation of starvation, at which time ketone bodies account for approximately one-fourth of the cerebral energy req uirements.