Nutrition refers to foods, nutrients, and other food substances important to health. Nutrients are food substances used for growth and maintenance; some nutrients are made in the body but others (or their precursors) are obtained from food. Besides being socially and culturally important, food is a basic need throughout the life span, providing energy and food substances that sustain life, health, growth, and development. Poor nutrition (malnutrition) can be inadequate or excessive energy and nutrients or some of both. This entry summarizes the role of nutrition in development across the life span.