Body composition refers to the relative proportion of body fat to lean body mass. Genetics, growth, diet, and exercise influence an individual's body composition. Essential body fat plays important roles like adapting to temperature changes, protecting organs, and storing energy. Healthy body composition, with body fat percentages within recommended ranges for teens, provides benefits like improved health, appearance, and longevity. Excess body fat increases risks for diseases such as cardiovascular issues, diabetes, and certain cancers.