Eat enough protein and don't overtrain...you will not lose muscle. If you want to look like a bodybuilder, it's about training more fast twitch IIb fibers for increased size and glycogen loading. Plenty of lean people have more strength and explosiveness and don't need to look like a BB to perform.
Heidi you have asked this question before, so my advice is see a local professional physician if you feel you are losing muscle tissue while still eating a ton of protein/calories. There may be other health issues going on. Don't continue using the IF approach if it is NOT working for you, that defeats the purpose. Unless you can monitor all variables routinely and find what works, don't just guess and make no changes and continue down a road of ill-health