anything (protein, carboydrate, fat) that is in refined form is an unnatural food.
It's easy to understand what refined sugar does (sugar is a carbohydrate). Refined protein also has devastating effects on your body - the effects are not yet in main stream media (I have a PhD in science).

The best food for your body is real food in whole form that has not been tampered with, isolated, refined or modified in any way.

Sugar is not bad if you were eating it raw right out of a sugar cane.