Counting Calories - In and Out

This is a fairly simple concept but it is worth explaining. Imagine your body is a car. You put in fuel, oil and water and off it goes. Occasionally you have to have it serviced, top up the battery or change a tyre, but generally speaking, as long as you keep adding fuel, oil and water, it will keep on going. It's a straight forward equation too, so many gallons of fuel will get you so far, not so far if you drive aggressively or overly fast. But for the purposes of this exercise, let's say, on average, you get around 600 miles out of your tank of fuel. You put the fuel in, and 600 miles later, you need to refill the tank. Simple.