If you take in whey protein during your fasting phase, you are NOT FASTING. Simple as that. You are "very low calorie, high protein dieting". This will damage you quicker than fasting.
Read Mark's extensive blog post series on IF and focus on the areas that explain why it is muscle sparing. What you are doing to yourself is unnecessary and cannot be recommended.
Pure protein during a fast is unproductive and even dangerous. You're better off eating pure fat, quite honestly. In the distant past, the OptiFast diet plan killed patients with protein exclusively (no fat, no carbs) in the context of a very low calorie diet so you know it isn't how your body was ever designed to function.
Last edited by GrokON; 04-28-2012 at 02:23 PM.
5'6" Female, 29 Years Old, 260/195/120
"Discipline is choosing between what you want NOW, and what you want MOST!"