Formula #1: Calories OUT > Calories IN = Weight Loss
This formula is as basic as weight loss gets. If you exercise more calories than you eat at the end of the day, you will lose weight. Creating a calorie deficiency at the end of a day does not mean you have to starve yourself. In fact, decreasing your calories too much can have an opposite effect on the body and cause what I refer to as CAMEL MODE.
The human body is built for survival and when we receive too few calories and not enough water, we can actually shut down our metabolism to a point where you will not burn fat and store water. So, you will not lose weight, but you could gain weight by the increased water retention.
Obviously the type of calories count. 500 calories of protein and fat have a different hormonal reaction with your body than 500 calories of carbohydrates. Make sure your macronutrients are in a decent balance of each. The 100 calories of a cookie is by no means equivalent to 100 calories of apple slices or steak. Eat smart!