It’s exceedingly difficult to deal with the box day in and day out when your body lacks fuel. And from experience I can tell you that extended fasting is all but impossible. After 2 days without food you may be able to complete the Wod, but by day 3 you will be useless. A tough pill to swallow if you are a competitive type like most cross fitters are
Granted that a lot will depend on the programming of your coaching staff, but even relatively light Metcons will suck royal donkey dick if you are post 24 hours since your last meal. Let alone some shit like Fran, Murph, etc.
Your OLY lifts will also become an even bigger struggle than normal, along with just about anything else that requires power and explosiveness (like thrusters)
Of course, you can likely track all of this yourself if your box uses an app like Wodify. Make a notation of your fasting status when you complete your workout. Over time it will be clear as day
OMAD or less is really your only reasonable option, and have your coaching staff give you feedback for meal planning. Though with OMAD the volume your going to need to put away, especially of protein is going to be daunting. Better start buying those huge 20 pound bags of frozen chicken breasts from Sams or Costco
While I don’t follow CrossFit properly. I do work really hard at the gym day in day out.
Sometimes you just gotta listen to your body.
My schedule is yoga at 3am. Weights at 8 3-4 days a week. Cardio after weights or on the non weight days. Electrolytes are critical when fasting and working out aggressively.
When going longer than OMAD I have to plan my workouts. In fact I find OMAD to be harder because I end up over eating in the window. I do better with 18:6 or 20:4.
While I have smashed a PR at 36 hours into a fast, I don’t plan on it. I program around having a light or easy day on day 2. I don’t maintain my workouts and even try to go past 48. I’m completely drained at 48 hours and recovery takes a whole day and I need a mid week rest day.
I know CrossFit programs 2 rest days a week usually. I would try to target day 2 of a fast a test day. Don’t push PRs. Just push for completion and SUBSTITUTE ELECTROLYTES EARY.