thats a tricky one isn't vinnd because the body doesn't handle fast stoppages of hormones the way it can vitamin supplements. i reckon the best option would be to continue taking the HRT but via a lozenger placed under the tongue during the fast so the hormones enter the blood stream without entering your fasting stomach. but if thats not an option for you, then i wouldn't make any fast changes and just keep taking them and perhaps 'gradually' lowering the dose if it becomes a long fast.