The causes of chronic systemic diseases are found among other things, not just nutrition metabolism.
First and foremost, there are diseases that affect the digestive system, but also Gelenkerkranungen, hypertension, arteriosclerosis, allergies, obesity and cancer be "wrong food" get chronic.
Causes absorbed. "poor diet":
Genetic predisposition for example (gluten / lactose intolerance)
food intolerances / allergies
incorrect composition of the diet,
too much on food,
poor eating habits,
bacterial, parasitic, viral infections / fungal infections
deficiencies in vitamins, intestinal bacteria