Weight maintenance occurs when we are in something called energy balance. Energy balance simply means:
Calorie Intake = Calorie Expenditure
Calorie Intake is simply all the calories you eat and drink daily.
Calorie Expenditure is a factor of three different things:
- Basal Metabolic Rate (BMR)
- Physical Activity
- Thermic Effect of Food
BMR: This is the amount of calories your body burns at rest daily to do all of its normal bodily processes. BMR accounts for 60-75% of your entire calorie expenditure. Muscle is more metabolically active than fat, therefore men have higher BMRs than women. The BMR decreases 3-5% every 10 years after the age of 30. Starving or fasting also decreases the BMR.
Since everyone’s metabolism is different, the only way to very accurately measure it is through something called indirect calorimetry. These are breathing machines that are able to calculate your personal BMR. I do this in my office and find it is an invaluable tool for weight loss purposes.
Physical Activity: This is the amount of calories your body burns while being active (not necessarily formal exercise), it accounts for 15-35% of your entire calorie expenditure. The factors that influence how many calories you burn during exercise are: how many muscle groups used (the more the greater calories burned), intensity, duration and body size.
Thermic Effect of Food: This is the amount of calories required to digest, absorb, transport, and metabolize the food we eat daily. It accounts for 5-10% of the total calories burned daily. Protein requires the most energy, and fat the least energy!
Weight Loss occurs when calorie intake is less than calorie expenditure
Weight Gain occurs when calorie intake is greater than calorie expenditure