Key factors affecting energy expenditure include basal metabolic rate (BMR), physical activity levels, and dietary thermogenesis. BMR is the amount of energy the body requires at rest to maintain vital functions, and it can be influenced by factors such as age, gender, and body composition. Physical activity encompasses all forms of movement, while dietary thermogenesis refers to the energy used to digest, absorb, and metabolize food. Understanding these factors can help individuals better manage their caloric intake and support weight management goals, leading to improved overall health.