Why do you need to eat to lose fat?

The yo-yo effect explained

Many people start playing sports or doing regular exercise because of their weight. A lot of them try to eat as little as possible (or nothing at all) when starting regular training, saying that first they want to lose excess fat. But they realise within a short time that the effect is just the opposite: after a drastic diet their scales show they are heavier. This is very discouraging!

The reason for that is our system's surviving mechanism. If consumption is reduced, the system switches over to energy saving. Judging from internal signs, your body's system draws the conclusion that it will get less nutrition in the future, so it reduces the fat burning so as to save the energy stored in fat. The level of metabolism will also drop. Your system will even use the protein of the muscles as a source of energy. Meanwhile it will send messages continually to the brain: "There is danger, we must eat! We must eat high calorie content food! We must eat!" The brain will win over the body; and the final result will be eating. As the weight of your body reduces, your system cannot burn nutrition with the same efficiency, so it stores fat. The final result is 5 kg more fat.

In order to lose weight efficiently, meaning burning excess fat reserves, we need to keep a net body weight and not lose muscle tone.