Good question ... and one that is not addressed in her book. I would say that if you find a protein powder that is high protein, low-carb (not sweetened with fructose, etc.) to go ahead and use it if you are comfortable with stepping away from the plan. Generally, her approach is very much "all-natural" so I would think she wouldn't be fore it. On the other hand, I do know that she is now recommending supplementation so who knows? I think this is very much a YMMV thing... I have successfully used a soy-based protein powder myself throughout.

Lisa