"This Kind" Moves on Fasting And Prayer

If we have heard one time, we have heard it three times how fasting and prayer moves unclean spirits. Sounds simple, so why not lay off the chips and dip for a day or two, most of our stomachs could use the rest anyway. But praying and fasting is not as easy as it seems. In addition to other issues, the evil spirits seem to have a hold on our appetities. Why can't we leave food alone even in a spiritual crisis?