My completely inexpert opinion is that if you're going to fast, then really fast. It's only for a day, or for several hours, depending on how you choose to fast. Water, or unsweetened teas are probably all you need or want. Does anybody really think you can lose much muscle over a single day? (I know a few people here tend to panic if they're not fed with protein circulating through their systems 24/7.) My personal, and uninformed opinion, based on no scientific evidence whatsoever, is that the benefits of fasting due to autophagy (a process of cellular "cleanup") could be far more beneficial to athletes than one more 24 hour period of amino acid loading. Heck, that Martin Berkham / Leangains guy looks pretty good, right? But WTFDIK?