**Abstract**

Sugars such as glucose or sucrose are considered hazardous foods because their intakes lead to obesity, further causing diabetes mellitus (DM), or cardiovascular diseases. However, glucose is needed for many brain functions such as memory and emotion among others. Glucose induces the secretion of insulin, which is needed for transportation of tryptophan from the blood to the brain. Serotonin, which is converted from tryptophan, is important for mood stability, control of emotion, and feeding is inhibited by serotonin in the hypothalamus. We discuss transportation of glucose from the blood to the glia cells. After glycolysis of glucose in the glia lactic acid is transported to cells such as glutaminergic neurons. After the release from neurons glutamic acid is taken up into glia cells and further to neurons again. Sucrose is degraded into glucose and fructose in the intestine thus intake of sucrose increases plasma levels of glucose. We show that intake of sucrose enhanced memory measured by Morris maze in rats and improved the working ability in humans. Roles of glucose and sucrose intakes are discussed together with the function of serotonin in feeding.

**Keywords:** sucrose, glucose, feeding, glucose transporter, glutaminergic neuron, Morris maze, working ability, glycolysis, astrocyte, serotonin, hypothalamus
