Hi mindful, sorry for the late response but I'll do my best to sum up why Mormon's fast.
Mormon's believe that fasting will help strengthen us spiritually while maintaining control over our physical bodies. During the fast, we may focus on a particular issue in our lives that needs resolution, pray for guidance, or express gratitude to our Savior. We are also believe that as part of our fast we are to consider and care for the poor.
A Mormon fast typically consists of abstaining from food or water for two meals or 24 hours. There has been no direction (that I know of) given for abstaining from anything other than food, such as sexual relations. On the first Sunday of every month Mormons' worldwide engage in a fast, although we may choose to occassionally fast on other additional days for personal reasons. and donate the money saved from abstaining from the two meals to the church in the form of fast offerings. The church then uses these fast offerings to distribute to those who are in need, most often the recepients are fellow Mormons.
As you may have gathered from this thread, the biggest challenge of fasting is preparing ourselves mentally to deal with the physical challenges. If you have any more specific questions, please feel free to ask.
On another note, I saw this article a few years ago and I thought you may enjoy it. It is about a Police Chief in San Jose, California who is Mormon. Because of the great number of Muslic citizens in his community, he joined them in Ramadan.
http://sfgate.com/cgi-bin/article.cg...AG7P9QRAM1.DTL