Calories are your body’s fuel, just as a car runs on gas or electricity. It’s not too farfetched to think of calories as miniature gallons of gasoline. Calories are your body’s source of energy to power your heart, expand your lungs, hug your mom, and walk and move your computer mouse – in short, they’re what your body uses to achieve every single physiological function it’s capable of doing.

Calories come from your food, but your body doesn’t simply take that chicken leg you just ate and throw it into some sort of biological furnace. First, your body must take the nutrients in the food and break them down into their smallest elemental form, a substance called glucose. If your body doesn’t need the energy for an immediate function, the calories get converted into body fat and stored for use later – like a savings account.

Every 3,500 calories that you save for later is the equivalent to one pound of body fat. You can only lose fat by creating a calorie deficit – either eating fewer calories than you use in a day or burning more calories than you eat in food. Once you take 3,500 calories out of your “savings”, the scale will show a one-pound weight loss.