My experience is that fasting helps the immune system. You don’t get sick as often. And when you do, you get well faster. Certain types of injuries heal better (sprained ankle healed fast as compared to similar injury few years earlier).
I attribute it to a combination of autophagy and gut biome improvements afforded by long term fasting lifestyle (I’ve eaten OMAD for over 3 years).
I can’t speak so much for starting the fasting after an injury or illness. I know seriously ill do sometimes try fasting in hopes of having the body heal itself. But not sure what a 72 hour fast would do after an injury. All I can say is try. Don’t think it would hurt. And might have a beneficial effect.
I’m certainly not a doctor, but I think in the very short-term when an injury is new, fasting wouldn’t necessarily help. For me, fasting has helped to reduce inflammation everywhere, which I imagine would help a ton for lingering injuries. I would think that in the short-term, the inflammation around an injury is maybe necessary or at least helpful in the healing process?