I was trying to show that the average protein recommendation for a 7-12 month old with the addition of 20% (since this is the average we as moms of CF babies are told to shoot for unless it isn't working for weight gain goals) is 16.2 grams/day. This is how they figure it out so I don't see the issue here. This might be a good starting point, along with the advice of a nutritionist, to determine how much is appropriate for this age. An adult male who has been dealing with CF for 20+ years is not comparable to an 11 month old.
If a child isn't having weight issues and is given too much protein, especially in a form that is difficult to digest, it can and does tax their system (especially the kidneys). There are medical studies that show this and CF doesn't have anything to do with it... it is how the body works. I believe we all, myself included, can do much of a good thing in an effort to feel better about weight gain. I know I had myself spinning my wheels many a time to "get more into him" when all it did was make him poop more (even with increased enzymes). It is a balancing act, one only a mom can observe and adjust to. We all have to be aware and try things, knowing our little ones are all different.
These drinks were not developed specially for a baby (not much less a CF baby), they are based on adult vitamin and protein requirements. Unless a qualified nutritionist or doctor is saying this level of protein, in addition to the formula or breastmilk the infant is receiving, is appropriate, I would not do it. THis is my feelings. Toddlers and above, different story.