1. If you spend more calories than you take in, you will lose weight. Just like your bank account, if you spend more than you put in, your bank account or, in this case your body, will shrink.
2. Adding (more) exercise, and not changing your diet at all, will cause weight loss only if you are burning more calories than you are taking in (as it states in rule 1). So if you are exercising enough to push the equation over to the deficit column (where you are basically in the red with calories - spending more than you are taking in), then you will begin to lose weight.
3. Reducing your food/caloric intake and not adding exercise will result in weight loss only if you have reduced food intake enough to tip the energy balance to the negative, whereby you are taking in less than you are expending.
4. Obviously, adding exercise, and reducing your caloric intake, will make it more likely that your equation will swing over to the negative – the weight loss side. And of course, the greater the difference between intake and expenditure, the faster the weight loss (or gain, depending on which way the equation swings).
