A healthy adult eats about a tonne of food a year. ‘Why eat?’ explores the need for food and the uses to which it is put in the body. We eat because we are hungry, but why have we evolved complex physiological and psychological mechanisms to control hunger, satiety, and our appetite for different types of food? Why are meals such an important part of our life? There is an obvious need for energy from food to perform physical work. Fats, carbohydrates, protein, and alcohol all provide metabolic fuels. In addition, the body requires two groups of nutrients—minerals and vitamins—but most important is the need for water.