Think about a car. What does a car need to make it run?
It needs the right fuel, it needs to be used (not stuck in a garage or on a drive) and it needs looking after (Tyres checked, water and oil checks etc.).
What would happen if, instead of petrol, we filled the car up with Cola? Sand? Alcohol?
It simply would not work.
Our body is like a car. To stay healthy we need the right combination of food and exercise to keep us healthy.