This is why body weight has very little to do with determining if you are overweight. The increase in metabolic rate with exercise lasts even after the exercise is finished. Dieting without exercise leads to muscle loss. Muscle cells are precious fat-burning factories. You must exercise to lose weight.
Exercise is the key.
If you vigorously exercise before you eat, you will eat less. Most people are not overweight because they eat too much. They're overweight because they're inactive. Weight loss depends on creating a demand for the energy stored in fat tissue. Dieting just won't do the trick, because no matter how few calories you take in, they must be used somehow, or they will be stored.