Day One!
I've wondered about the variety myself. I didn't have to change my diet as far before surgery as most did because I already followed a high protein low carb lifestyle for about 2 years... it is second nature to me now... but there are some with radically different eating habits that will be told to start the high protein low carb sooner... then the pre-ops... no clue why they vary... my doc told us it's 2 days because then it cleans out your system pretty well and gets the tummy good and empty which leads to less complications/gas/etc...
HUGS, hope that it helped... I'm 2 hrs from no liquids... YIKES... I feel thirsty all of a sudden! LOL... gonna go take my meds and have a good night's sleep so I can be cut open while in good spirits tomorrow... I'm looking forward to this!
HUGS
Rachel