BMR

You use energy no matter what you're doing, even when sleeping. Your BMR (Basal Metabolic Rate) is an estimate of how many calories you'd burn if you were to do nothing but rest for 24 hours. It represents the minimum amount of energy needed to keep your body functioning, including breathing and keeping your heart beating. Easiest ways in which you could calculate your BMR is by using the bmr calculator available here. Your BMR decreases as you age. Likewise, depriving yourself of food in hopes of losing weight also decreases your BMR, a foil to your intentions. However, a regular routine of cardiovascular exercise can increase your BMR, improving your health and fitness when your body's ability to burn energy gradually slows down.