Regional brain glucose hypometabolism occurs during aging and may contribute to the onset of
aging-related cognitive impairment in humans. Ketones are the main alternative energy
substrate to glucose for the brain. Several studies show that brain ketone uptake and
metabolism are unaltered in cognitively-normal older persons and in Alzheimer's disease (AD).
Nutritional ketosis is reported to have a positive impact on cognitive performances in mild
cognitive impairment and AD. Nevertheless, changes in regional brain glucose and ketone
uptake in adults are poorly understood during diet-induced experimental ketosis. The
investigators hypothesis was that during diet-induced ketosis, brain ketone uptake would be
directly correlated with the elevation of blood ketone levels and inversely correlated to
brain glucose uptake.