The body has an instinctive system which allows it, through senses (notably smell and taste) to know if you need one particular food or not.
How good the smell and taste of something are, is determined by how useful this food is for you and how healthy (full of micronutrients, for example) It is.
The thing is, It only works with natural food, notably fruits, vegetable and nuts. (I don't know about raw animal food).
This is why one particular fruit or veggie can be very attractive at one point, and repulsive at another.
Also why they are less and less tasty as you get full.
Processed food override and abuse this system. They always taste the same = good, so you eat bad things and too much.
