Protein powder in your carry on?
If there is any doubt, why not just put it in your luggage? Surely you can survive the flight without protein powder. Just make sure it is in the center of your clothes protected from all sides. Baggage handlers are not known for finess. Another thing you might consider is somehow making a copy of the label from the powder and putting it in the bag visible to whomever might see it. I usually put the whole label in there. The side with the product name, and the side with all the nutrition info too. I do this with my vitamins too. I put all my daily packs in one big zip lock with a list of everything that's in there. I've never had a problem.
DS on 04/17/13