If the cancer is in your genes and your body is weak to prevent it, you will become cancer at some point. Everyday our body produces cancer cells and destroy them quickly. However, if you are weak, vulnerable your body can not fight with the cancer .You can delay it.Maybe, if you can protect yourself; you can avoid it for many years.However about your question ,you must do all of these things ''drinking enough water,eating a low fiber diet, avoiding tobacco'' etc, You can add so many things into that list. Stay away from stress, don't drink alcohol or stay away from to much radiation.
One way in determining your fitness level is trying to do a Full Sprint Run and holding your breath for as long as you can. That way you can determine your cardiovascular capacity and lung capacity. On improving your fitness levels you should do swimming, jogging and of course a balanced diet.
