Final answer:
Age is the factor that affects resting energy expenditure (REE) among the options provided, with BMR generally decreasing as age increases.
Step-by-step explanation:
The factor that affects resting energy expenditure (REE) among the options provided is age. Numerous elements influence basal metabolic rate (BMR), including body temperature, age, sex, hormones, and body composition. Among these, age is known to affect energy expenditure; as we age, our BMR typically decreases.
Additionally, factors such as body surface area, which relates to height and weight, and total body weight also have a significant impact on BMR. Weight especially plays a role because heavier individuals tend to have a higher BMR. Athletes may have an increased BMR due to a higher amount of lean muscle mass, which burns more calories than body fat.