What is glucose sparing?

Glucose sparing refers to the physiological process where the body conserves glucose by relying on alternative energy sources like ketone bodies or lactate. This mechanism is particularly vital during fasting or traumatic conditions when glucose needs to be conserved for essential functions.

When fasting, fat from fat cells is released and converted into beta-hydroxybutyrate (a ketone body) by the liver. The brain, which cannot use fat directly but can use glucose and beta-hydroxybutyrate, shifts to using these ketones, thereby sparing glucose. This conservation of glucose is crucial because, after prolonged fasting, the body would otherwise start breaking down muscle proteins to produce glucose, which could lead to significant muscle loss 1.

In the brain, glucose sparing happens when neurons use lactate instead of glucose for energy. This lactate can come from astrocytes in the brain and is transported into the neurons. By using lactate, glucose is freed up for other critical biosynthetic pathways, such as generating NADPH for antioxidant production (e.g., glutathione) which is crucial during oxidative stress or brain injuries 2 3. This glucose sparing effect helps maintain brain function during periods of high demand or stress.

Overall, glucose sparing ensures that glucose is available for critical bodily functions that cannot use alternatives, thereby preserving muscle mass and enhancing brain resilience 4.