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We understand your concerns
I went through your details. I suggest you stick to the fasting methods. Almost every people in your religion do the fasting and none of them are asking these questions. Even if they does, there is no perfect answer. Fasting is good for health and it cleanses your system. You cannot eat stomach full of food before sunrise and after sunset. The dietary juices would have become weak to digest it. That is the requirement of fasting.
As you asked, whole grain and fibrous food are the best which can last long inside the stomach. But none cannot last more than 6 hours. Believe in god and he will take care of you while fasting.
You might need psychological counseling
. I can help you through telephone. Please do contact me through customer care of www.healthcaremagic.com for a telephonic consultation session.
Hope this answers your query. Available for further clarifications.