We prefer that you stick to one type of flour per starter for the first 15 feedings; but after you submit your data, you can feed your starter whatever you like. As with so many other questions, there hasn’t been any formal research into the effect that a “change in diet” might have on the microbial community or behavior of a sourdough. But, anecdotally, many bakers have shared that the same sourdough starter might act differently when fed different types of flour.