Final answer:
Calories needed to maintain weight is determined by factors such as a person's age, activity level, and sex/gender. A basal metabolic rate and level of physical activity are both crucial in calculating total daily energy needs. Blood type does not affect this calculation.
Step-by-step explanation:
The options that determine the number of calories needed to maintain weight include a person's age, a person's activity level, and a person's sex/gender. A person's blood type does not play a role in determining caloric needs. The basal metabolic rate (BMR), which is influenced by age, sex, and body composition, is a critical component in figuring out an individual's calorie requirements. In addition, the overall level of physical activity significantly impacts how many calories a person should consume to maintain weight. It's the combination of BMR and physical activity that will determine the total daily energy expenditure (TDEE), defining how many calories a person needs to maintain their current weight.
Calorie needs are not static and may change over time due to factors like aging, changes in muscle mass, hormonal shifts, and adjustments in activity levels. To maintain weight, one must aim for a caloric intake that is equal to the calories used by the body for basal metabolic functions and physical activities. Any significant discrepancy between caloric intake and energy expenditure would lead to weight changes, whether it's weight gain or loss.