When it comes to Physical Fitness diet is very important. Imagine a person who eats only fast food but expects to be fit like an athlete. The truth is you can only do so much with exercise alone. The food a person eats is essentially the fuel for a person throughout the day to create energy and get nutrients. Think of a car that needs gasoline and oil. If you pick the wrong kind of oil it can have an affect on the lifespan of your car and without gas the car will not run.