Fat goes first. Saying that a theoretical body builder who isn't even trying to make a certain weight loses 'significant' muscle is not something that's backed up by even common sense. If that were true, how does anyone end up with more muscle after they lose weight?

> 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?