What if the fuel your brain uses could influence how clearly you think, how well you focus, your mood, and even your long-term brain health?

The human brain is metabolically flexible. It can use two main fuels for energy: glucose, which comes from carbohydrates, and ketones, which are made from fat by the liver (or body fat).

Because most people eat carbohydrates regularly throughout the day, their bodies rarely produce significant amounts of ketones, so glucose becomes the brain's main fuel by default. However, during fasting, prolonged exercise or by reducing dietary carbohydrate, the body begins producing ketones, providing the brain with an alternative source of energy.