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Body composition is influenced by a range of factors, making diet, physical activity, genetics, age, and hormonal balance critical components in determining how much fat versus lean mass is present in an individual’s body.

Genetics plays a foundational role by determining body shape, metabolism, and muscle fiber composition, which all contribute to one's predisposition toward gaining or losing weight. Diet is essential as it provides the necessary nutrients and caloric balance to either promote fat loss or muscle gain. Physical activity directly impacts body composition by influencing energy expenditure and muscle development. Age also matters, as metabolic rates typically decline with aging, affecting how the body processes food and stores fat. Lastly, hormonal balance—including hormones like insulin, cortisol, and testosterone—affects body fat distribution and metabolic processes, leading to variations in body composition.

Other options, while they may influence aspects of health or fitness, do not encompass the comprehensive array of factors that significantly impact body composition. For instance, focusing solely on diet and exercise neglects the genetic and hormonal factors, which are equally pivotal. Similarly, weather conditions and geography are not primary determinants; they may affect exercise routines or food availability but do not inherently alter body composition in the way the listed factors do.