Many, many years ago everyone was strong and healthy. They ate a very varied diet, and especially loved fruit, vegetables, and fish. Everyone took daily exercise, and they enjoyed themselves playing and leaping about. The earth was the healthiest place you could imagine, and it was clear that both adults and children were full of joy and good moods. All that made the dark witches furious. They only ever wanted to do harm and make problems for people. The worst of all of these witches was sourface; she was evil, and could be relied on to come up with the nastiest ideas. She suggested that all the witches combine their energies to invent a potion which would take away people's desire to live happily. So, one night, all the witches gathered down in the swampy forest and worked together on that evil spell. The spell was so powerful, and would need so much energy to cast, that when one of the witches got one of the words wrong, there was a huge explosion. So big was the explosion, that it completely destroyed the forest. It turned all those evil witches into tiny little creatures, like germs, and left them trapped in a green liquid inside a small glass bottle, which lay lost in the swamp. There they were trapped for centuries, until one day a little boy found the bottle. Thinking it contained some kind of soft drink, he drank the lot. The evil, microscopic witches took advantage of this situation, and even though they were tiny and couldn't hurt anyone, they soon learned to change the little boy's likes and dislikes in order to get him to do what they wanted. In a few days, a funny feeling in his mouth and tongue meant the boy no longer wanted to eat vegetables, fruit, or fish. All he wanted to do was eat ice cream, pizza, burgers, and candy. Then a nibbling feeling all over his body meant he no longer enjoyed playing and running about with his friends. All that stuff tired him out; he now just wanted to stay in the house, sitting or lying about. So, his life got more and more boring, he started feeling ill, and before long he had no desire to do anything. The evil potion had worked! And the worst thing of all was that the witches learned to jump from one person to another, like a virus. They managed to turn the influence of the potion into the most contagious of diseases: the disease of wasting your life. It was a long while before, with the help of his microscope, doctor fitton-helthie discovered that the little witches were causing all this disease. There was no vaccine or cough mixture to get rid of them, but the good doctor discovered that the witches could not stand joy and good humour. It turned out that the best cure was to make a strong effort to live a healthy, joyful, and happy life. When a person became healthy, the little witches would leave that body as soon as they could, riding off on a sneeze. From then on, the best remedy was not pills or injections, but just a little bit of effort to eat some fruit, vegetables, and fish, and to do some exercise. And whoever came to see doctor fitton-helthie, and took his advice, ended up totally well, being cured of the waste-of-life disease. 
Although you have to make some effort to live a healthy and happy life, it pays to eat a little of everything, and do some exercise. 