Seyed Ali Shobayri, Seyed Ali Shobayri is of mixed Iranian and Scottish descent who found the path of the Ahlul Bayt (a) by his own research. He holds a BA in Islamic Studies from Middlesex University through the... Answered 2 months ago

Bismillah, 

Asalamu Alaykom, 

It is makruh to do things which would make one weak while fasting such as giving blood. It still would be permissible to do. 

May Allah grant you success