But instrumental fasting is all but impossible to find in the pages of the Bible and is rarely reflected in ancient Judaism or the rabbis. Instead of an instrumental approach, the genius of the Bible is its focus on the whole-body response of a human being to grievous, severe conditions. Fasting means a human being refrains from food or water, or both, for a limited period of time in response to some sacred, grievous moment.— Sermon on the Mount, pages 193, 194
Scot wrote a whole book on fasting, developing this thought even further. Do yourself a favor and read it!