Why are the pounds removed slowly as they return very quickly?

Weight control is based on balance between the consumption of calories and the energy you spend over a day.
The weight control area of the brain is the hypothalamus.

The hypothalamus integrates the signals from the brain and then controls the weight influenced by hunger and satisfaction.

Even after dieting, the body strives to combat weight loss by reducing energy consumption.

When you start losing weight, your body is taught to preserve food, and your metabolic system slows down. So after you stop dieting the risk of weight gain is huge because metabolic is still working slowly.

Only if you continue to maintain a healthy life - style and exercise, can you avoid weight gain.