I can’t speak on 72 but I’ve been doing three 48s a week since November. The only downside I’ve experienced is the occasional gerd with me needing to drink acv to relieve.
There’s a guy on YouTube who’s been doing 48s for 2 years straight but his meals are like 6k-7k calories.
I think it comes down to your body fat percentage as well as the nutritional density of the foods your eating as well as their adsorbability when you do eat. You’re always eating whether your fasting or not but if your not feeding micronutrients your body will always want more to try and get what it needs.
I’m by no means an expert, I’ve done 18-6 for while now and it works fine.
I’d be curious to understand your reasons why. Are you fasting for weight loss? Is this some kind of challenge? My main concern when I see these types of posts is are people going to develop some kind of eating disorder or have a unhealthy relationship with food when imposing such crazy restrictions long term. As I say, by no means an expert but curious none the less.