This is called "yo-yo" dieting - which is a common result of many ordinary diets.

The fact is, the more you "yo-yo" diet, the harder it is to lose weight once you put it back on. Plus, yo-yo dieting can be very dangerous, whether you're 15 years old or 50 years old. Putting your body through a constant state of change can be very hard on your vital organs, and disruptive to your body's systems.