I am close to your stats and activity level now and for the last two months I have been doing 72 hour fasts with the refeed being 1 part sirloin steak (say 6-8 oz) to 2 parts veggies (type varies but just a Walmart frozen bag). I am not exact on the weight of either I just eyeball it.
Body will consume fat over muscle if you continue (lite)training(don’t come near over exertion). Maybe you’ll lose a little bit of muscle.
Steak is perfect… Eat slowly and be mindful of your stomach and notice how your body reacts to the food, some people have adverse reactions when re-introducing.
Some people, like myself, the body depletes electrolytes too fast, and training will deplete electrolytes rapidly. so keep that snake juice nearby or else you’ll find yourself craving desperately. Consider supplementing magnesium. That’s it!