Final answer:
To estimate the calorie needs using the Harris-Benedict equation, consider factors like age and activity level. Calculate energy expenditure via physical activities, such as climbing stairs at 150W with 20% efficiency, to understand how long it takes to burn calories from food.
Step-by-step explanation:
The Harris-Benedict equation helps estimate an individual's calorie needs based on factors such as gender, age, weight, height, and physical activity level. Using this information, alongside knowing the calories in food items and the energy expenditure of various physical activities, one can manage their calorie intake and expenditure to maintain, lose, or gain weight.
For example, if a snack has 250 Calories (kilocalories), and you want to burn this off through exercise at an efficiency of 20%, exercising at a rate of 150 watts (such as moderately climbing stairs), you would need to determine how long it would take to expend that energy. In this scenario, because the body is only 20% efficient, the actual energy used is five times what is produced. Therefore, 250 Calories would take 833 kilojoules of work (since 1 Cal = 4.184 kJ), and at a production rate of 150 watts or 0.15 kJ/s, this would take approximately 5,553 seconds or 1.54 hours of exercise to burn off.
Remembering the thermochemistry of weight maintenance, gaining, and losing is important. To maintain weight, one should balance calories consumed with calories used. To gain weight, one must consume more calories than expended, and to lose weight, one must consume fewer calories than expended, with the conversion being approximately 3,500 Calories to a pound of body weight.