I know very little about Buddhism but in Celtic traditions fasting or prayer fasting is a type of vision quest. Normally for a period of 3 days and 3 nights you would abstain from food and isolate yourself. The old druidic view of this act is that the power of fasting affects the shamanic reality of things, the soul energy of a person begins to influence the shape of the world. By ignoring the body, you raise your consiousness and see things that ordinarily you would have missed.