Brain Fact # 13
Food for Thought
If you were to inject a blue dye into the blood stream of an animal, tissues of the whole body would turn blue – except the brain and the spinal cord. This is due to the presence of the blood brain barrier which prevents some materials in the blood, such as bacteria, from entering the brain. The blood brain barrier works to maintain a constant environment for the brain while allowing the movement of essential molecules into it.
Two essential molecules that are allowed into the brain are oxygen and glucose. The brain’s energy requirements are far out of proportion to the 2% of the body’s total weight that it represents. The brain receives 15% of the cardiac output, and consumes 20% of total oxygen and nearly 20% of total glucose utilization. This means that the brain extracts approximately 50% of the oxygen and 10% of the glucose from the arterial blood. These are incredible number considering the small size of the brain.
Glucose, a form of sugar, is the brain’s source of fuel. Because brain cells cannot store glucose, they depend on the bloodstream to deliver it. Glucose in the blood comes mostly from carbohydrates, that is the starches and sugars that we ingest in the form of grains, fruits and vegetables and dairy products. These complex carbohydrates are broken down slowly and delivered to the brain. Simple carbohydrates (most processed and sugary foods) break apart quickly and are rapidly released into the bloodstream and they rapidly raise your blood sugar level and give you a quick brain boost. The effect is short-lived however, because the hormone insulin signals cells to pull the excess glucose from the bloodstream and store it for later use. Neurons are unable to store glucose however and so they quickly deplete their fuel.
Our brains need glucose to function and there are different ways to get it with some foods (mostly natural ones) providing a better, slower and more constant source of fuel than others (processed and high sugar foods). This has important implications for brain performance as eating a healthy diet is an important factor in brain functioning.