I just noted a comment on an old blog post - found here - that dealt with fasting and Luther's noting that eating or not eating is fine as long as sin or righteousness isn't attached to it.
A few days later Chad Myers asks as follows:
Then what is the point of fasting? Jesus himself said this was necessary in some circumstances (when he came down the hill after the Transfiguration and told the disciples that some demons can only be driven out through prayer *and* fasting.
AFAIK, Luther advocated fasting as well:
"Of fasting I say this: it is right to fast frequently in order to subdue and control the body. For when the stomach is full, the body does not serve for preaching, for praying, for studying, or for doing anything else that is good. Under such circumstances God's Word cannot remain. But one should not fast with a view to meriting something by it as by a good work" (What Luther Says, St. Louis: Concordia Publ. House, Vol.1, 1959, p. 506).
I think this hits to the point of difference between a Roman and a Lutheran understanding of Good Works. To the Lutheran, the point of works are not that if we don't do enough God isn't pleased, or that we must earn up the brownie points with God. Good Works for a Lutheran are simply things that flow out of the Christian life that end up being beneficial (for the neighbor or for the self).
Take for example fasting. Again - do not fast so as to think you are meriting salvation for your fast. Rather - it is good for self-discipline. It is good for the tending of others (I'd say fasting goes along with casting out of the demons because in many ways to deny the self is to deny the prince of this world who would try to rule over you with your passions and desires). It is good -- it just doesn't cause or add to salvation. It is a benefit now in this temporal life.