I've looked for this quite a bit. Bottom line, I don't think the answer is really known. I feel safer staying firmly in ketosis than slipping in and out. Partially I base that on reading that there a tiny amount of your body taking muscle for glucose in the early stages of the crossover, which then resolves itself before you get into ketosis. I've never heard that this is any kind of problem and have never myself experienced any problems the many times I've slipped in and out but still overall, feel safer sticking to one or the other (mostly just one).I have exactly the same question. Hopefully someone knows the answer.