This document provides an introduction to food, including its definition, physiological functions, and social and psychological roles. It defines food as any substance that provides nutrients to support an organism. Physiologically, foods are categorized as energy-yielding (carbohydrates, fats), body-building (proteins), or protective/regulatory (vitamins, minerals). Socially, food connects communities and symbolizes acceptance. Psychologically, food satisfies emotional needs like security, love, and acceptance. The document also notes that foods are commonly grouped according to their nutritional value to aid in diet planning.