In a well-fed state, brain cells use which one of the following compounds circulating in the blood stream almost exclusively as an energy source?

Glucose is virtually the sole fuel for the human brain, except during prolonged starvation. The brain lacks fuel stores, thus requires a continuous supply of glucose. It consumes about 120 g daily which corresponds to an energy input of 420 kcal (1760 KJ), accounting for some 60% of the utilization of glucose by the whole body in the resting state.