Hi, I think that’s great that your interested in helping your friend. My name’s Breanna, I’m 15 and like your friend I have PKU. As of right now it may not be a problem for your friend but it will get to be, after awhile your friend could experience things like headaches, vomitting, tremors or shakes, loss of balance, more irritable, harder to concentrate, lower IQ, harder to follow simple instructions and over all poor health. nAlso if your friend has a child in the future and isn’t doing good with her diet and gets pregnant it can cause issues. If a woman has a baby while either off diet or having poor blood levels (not sure how much you know about your friends pku) it can result in a miscarriage, or the baby could be premature, be mildly to severly retarded and could have heart problems. So yes your friend being off of the diet or doing poorly with the diet can effect her. If you really are interested in helping her it might be a wise idea to talk to her parents or siblings if she has any. Basically someone with PKU eatting poorly can be just as intoxicating as getting extremely drunk. nBreanna Oh if you have any other questions I’ll be happy to answer them.