In the bible fasting is going without food but still drinking water or juices. Whatever bread you have been feeding yourself (and maybe that bread is radio or tv or junk food snacks) that is getting in the way of God.
When we fast, we use that time to pray and spend time with God. Its not like dieting, which is just as a means to lose weight.
To answer your question how do you know if God is leading you to do something. Good question. Well I know if it comes from above and not myself as I wouldnt have thought of it myself, and nobody else has told me. I will know in my spirit. Perhaps I had prayed about something and then God gives me a scripture to encourage me to act.
Before Jesus started his ministry, he was led by the spirit into the wilderness for 40 days. Was it his own idea to fast or God's? Well in the wilderness he didnt have any food, because there simply wasnt any, and we dont know if he took food on his journey and then ran out, but the important thing was He spending that time with God with no distractions. Because the food we eat while fasting is spiritual.
