Most of the time, nutritional yeast should be okay. It may not work in someone who has developed cross-sensitivity to yeast or yeast products. I don't find that nutritional yeast is always problematic in someone who has candida. As one researcher put it, the two organisms can be "millions of miles apart" when it comes to similarities. In other words, one species can vary quite a lot from another, and cross-reactivity may not be present.