I mix a vegan meal replacement in with my coffee and make it like a flavored coffee.
I didnt eat any meats for a long time preparing for this fast. I didnt need it on past fasts at all. I would not do it every day or very frequently. People have died using protien mixes during fasting. So its not something you can just have every day or a lot.
If I just started fasting I would not use them at all. There is most likely no need.