Geo,
Hello! Good questions.
Well, I would have to say that the eating of candy bars and whatnot is okay, as long as it isn't contrary to temperance. I certainly don't eat them solely for their nutritional value. Even St. Teresa of Avila, as Michelina once shared with me, throughly enjoyed a certain bird, saying, "Penance is penance, pheasant is pheasant."
It really is a matter of conscience as to whether or not one is indulging beyond right rule of reason. For example, at weddings you may have wonderful foods and at times of celebration partake of a good meal, and harty company. Even the Book of Ecclesiastes mentions the goodness of a table partaken of with thanksgiving, and with good manners befitting a man in control of his appetites. It is when food becomes an end, and not a means, that a disorder takes place.
If I may go on a personal note, all my life I have been practically indulged to the point of thinking that almost every irrational craving I have for food is a need; now I am more discerning regarding my hungers, trying to offer them up for God, and saying in my heart, "Lord, I will give up these good things to love you. You are the food of my soul." So even though having a brownie after dinner isn't bad, there are different means for different souls. A Priest, Brother of Sister may be able to observe more rigorous abstinence then say a lay person, because of their state in life.
I hope this answers your question.