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Generalized decrease in brain glucose metabolism during fasting in humans studied by PET.

C Redies¹, L J Hoffer, C Beil

¹McConnell Brain Imaging Unit, Montreal Neurological Institute, Quebec, Canada.

The American Journal of Physiology

|June 1, 1989

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This summary is machine-generated.

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During prolonged fasting, the human brain uniformly reduces glucose utilization. Ketone bodies become a primary energy source, decreasing reliance on glucose across all brain regions.

Area of Science:

Neuroscience
Metabolic Research
Human Physiology

Background:

During prolonged fasting, the brain shifts its primary energy source from glucose to ketone bodies.
Previous studies indicated regional differences in brain energy substrate utilization in rats, but human data were lacking.

Purpose of the Study:

To investigate regional brain glucose and oxygen metabolism, blood flow, and blood volume in obese humans undergoing a 3-week total fast.
To compare these metabolic parameters before and after the fasting period.

Main Methods:

Utilized Positron Emission Tomography (PET) to measure regional brain metabolism and blood flow.
Assessed glucose and oxygen utilization, blood flow, and blood volume in four obese subjects.
Compared measurements from a postabsorptive state to those after a 3-week total fast.

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Main Results:

Whole brain glucose utilization decreased significantly to 54% of control values (P < 0.002).
The rate constant for glucose tracer phosphorylation also decreased uniformly throughout the brain to 51% of control values (P < 0.002).
Regional blood-brain barrier transfer coefficients, oxygen utilization, blood flow, and blood volume remained unchanged.

Conclusions:

The human brain uniformly reduces glucose metabolism during prolonged fasting.
This metabolic shift suggests a widespread adaptation to utilize ketone bodies as a primary energy source.
Fasting does not alter regional cerebral blood flow or oxygen consumption in the human brain.