If you have an ileostomy and are fasting during a religious period,bowel habits will become more erratic. Reducing fluid intake may make you become dehydrated and you may feel light headed, thirsty and develop a headache. It may be advisable to discuss observance of these fasting periods with your religious leader.
Feasting/fasting may also effect the way your medicine works or are absorbed by the body. It may be advisable to talk to your GP or local pharmasist as they will be happy to discuss any aspect of your medication or other concerns with you.