What is the main source of energy for the central nervous system and brain?

The central nervous system and brain primarily rely on glucose as their main source of energy. Glucose is a simple carbohydrate that can be readily transported across the blood-brain barrier, making it particularly essential for neuronal function. The brain consumes a significant amount of glucose relative to its size, accounting for about 20% of total glucose utilization in the body. This is because neurons require a constant and efficient energy source to maintain their activities, including neurotransmission and maintaining the integrity of the neural network.

Although fats can serve as an alternative energy source through ketone bodies during periods of prolonged fasting or low carbohydrate intake, under normal circumstances, glucose is the preferred and most efficient energy substrate for brain activity. Proteins do not serve as a primary energy source for the brain; rather, they are mainly used for repair, growth, and maintenance of tissues. Fiber, while important for digestive health and regulating blood sugar levels, provides no energy in the form of calories.

In summary, glucose is critical for the functioning of the central nervous system and brain, which is why it is considered the main source of energy for these organs.