Protein converts to glucose with 58% efficiency. Whey protein digests very quickly, which means it can convert to glucose quickly. This will elicit an insulin response, and knock or keep someone out of ketosis temporarily. Theoretically. Ketosis is a hard thing to gauge. So long as you're getting under 100 grams of carbs per day, you will be producing ketones to some degree.
i just saw a picture of ceebs over at another board. i think she knows what shes talking about,