Synesthesia, or cross perception, is a condition in which a person perceives stimuli not only with the sense for which it is intended, but with others as well. For example, a synesthete may see musical notes as color hues or feel flavors as different textures on the skin. Experiments have determined that the linking of the senses occurs because of some unique physical condition in the brains of these people. For example, blood flow to some parts of the brain, normally increased by sensory stimuli, decreases in synesthetes.

There are six essential nutrients: carbohydrates, fats, proteins, water, vitamins, and minerals. Energy nutrients are those that provide the body with the majority of the energy needed for daily metabolic reactions. Carbohydrates, fats, and proteins are energy nutrients.