By taking an honest look at nature, we will observe that:
1) Nature follows definite laws
2) These laws are not subject to opinion or variance
3) Every aspect of life is reflected by nature
4) Nature is governed by the law of Cause and Effect
If we violate a natural law, we create a Cause, for which we will suffer an Effect.
Our ignorance of the Laws of Nature doesn't change these laws.
There are two reasons for disease, or lack of health:
There are a few good rules to follow to achieve health.
1) Follow the Laws of Nature
2) Let Truth be your authority, not authority your truth.
One of the Laws of Nature is that the innate intelligence of the body strives to keep the body alive, regardless of the cost.
The "cost" is what we call "disease". Disease is the effort of the body to keep us alive.