In the past, I found the first week ultra challenging, and the 2nd week somewhat challenging, when transitioning from OMAD (my default) to 47:1. This takes into account that I do everything ‘right’, as in lowering my carb intake a bit in advance, and for me personally also getting a short trip to tanning saloon. (I suspect my vit.D is low because I find 47:1 near impossible to sustain, without tanning a tiny bit, twice a month.)