From Christianity Today online.

Fasting can train and shape these [subconscious] processes, giving us the ability to exert control over other desires. One study found that students who intentionally practiced good posture for two weeks showed significant improvement afterward on measures of self control. The ability to control our relationship to food is, of course, one of the most difficult of the disciplines. Self control is like a muscle; it can be exhausted by overuse, but it can also be strengthened with exercise.

An interesting piece. Read it all.