Will they allow the powder and then you can just mix it with the water they provide?
Good question. There is no formal written guideline yet, which typically takes about 4 weeks. For now, it only applies to liquids and gells (although reports indicate that inspectors have also taken items such as mascara and lip gloss). I'm not so sure that a protein in a powder form would be allowed, given that many lethal substances can be transported in powder form (e.g. anthrax).
In my view, there is a significant chance that carry on luggage will be banned altogether as the process of hand searching every bag for liquids and gells may be too burdensome to work. Stay tuned.