Since there are so many different PKU mutations doctors can’t really say if all people with hyperphe or all people with Classical PKU will respond. I have classical PKU and I went from being allowed 300 mg of phe (or 20 exchanges) to 1000 mg of phe (or about 68 exchanges). So I responded great! You just have to give it a try and see what happens. Lol, I know what you mean. I’ve been on diet all my life and will never go off but I’m not perfect.