Energy, often referred to as the calorie content of a food, is derived from the carbohydrate, protein, fat, and alcohol found in foods and beverages. Although vitamins and minerals are essential to the body, they provide no energy. The human brain is metabolically very active and uses about 20 to 30% of a person's energy intake at rest. Individuals who do not eat adequate calories from food to meet their energy requirements will experience changes in mental functioning. Simply skipping breakfast is associated with lower fluency and problem-solving ability, especially in individuals who are already slightly malnourished. A hungry person may also experience lack of energy or motivation.