As your body takes on fat, your fat cells grow in size, and if your caloric intake is extreme, you can even develop new fat cells. When you lose fat, cells shrink, become unhappy, and fight to regain their lost fat. The shrinking fat cell will cause a decreased breakdown of fat and an increase
in fat storage. Because of this metabolic phenomenon, appetite for fat foods usually increases.Further, extra fat cells created by weight gain never go away. The number stays constant even with a large weight loss. That's why it's so difficult to maintain the weight loss. 

The body defends its fat as if filled with unhappy cells demanding attention. Your weight loss strategy must not only include reducing the amount of food you eat, but also an exercise program. Exercise fires up your metabolic engine and forces the fat cell to give up its fat. With exercise the body's system to preserve its fat stores is overridden by its need to provide an energy source for the increased activity.

What is the message? Don't overeat, limit the fat intake, and exercise. Did you get the last point there? EXERCISE. Remember, your fitness center is there for you, so don't make those fat cells smile!