Lets talk diet. That word just means the food you eat. If you want to be healthy, then put good foods into your body. Your body will tell you what it needs. If you need iron, you will crave iron rich foods. It holds true for all aspects of your diet. The body has requirements. There is a  complete vitamin and mineral list. It tells what the vitamins are and why they are important. But every body is different, and therefore has different requirements. If you think it is one size fits all, then you are sadly mistaken. The good news is, it is easy figure out for yourself. If you want to lose weight, the right diet will easily shed the pounds. If you are not losing weight, then you need to rethink the diet. As with everything moderation, sensibility, and trial and error will help you determine what is best for your body. Yes the body has nutritional requirements, and if you give it everything it needs, then your body will be healthier. And as far as sickness, all sickness, there is a dietary deficiency which is contributing to it. If you think about it, almost all the problems inside you can be traced back to what you put in.
I am still working on the nutrition guide to give you a better understand of the body processes food.