> It's not a healthy way to live, and it's not undertaken by these athletes unless strictly necesssry
That's not the discussion, this has nothing to do with whether fasting destroys muscle mass.
Do you have anything to back up your claim?
They try to rid their body of as much water as possible to lower their weight.
When we say fasting for health it usually means lots of water, but no calories.
It isn't that MMA cutting is healthy, it is that fat is burned first, not muscle. Fasting for a day here and there isn't going to make someone 'lose all their muscle mass'.
When fighters cut just before weight in, they do so to make sure that they make their weight class cut off or they can't compete. This has nothing to do with fasting - they are forced to do it to stay in weight class, but at the very top of it (being as heavy as possible is overall a boon in the ring).
The idea that you think 'fasting' loses muscle mass is an idea that is not backed up by any evidence. Fasting isn't a diet, it is about when you eat.
Also, you didn't source anything. Don't you think maybe the dozen people replying to you might be less likely to be 'making stuff up?'
For 1. you can see MMA fighters cut weight and not 'lose all their muscle mass' so that one seems to have some pretty stark evidence against it. Not to mention that body builders routinely go on bulking and cutting cycles specifically to put on more muscle.