It can be done. I was off-diet from age 3 until about 32. In a sense, I did go back on-diet slowly, but that was just a matter of trying to determine what my optimum level of dietary protein and formula was. Now, I’m on Kuvan and eating 45g of protein from food, and pretty stable with my level staying around 6. How difficult being on-diet is varies, for me it’s not a big deal (partially due to the fact that I have such a high tolerance, particularly on Kuvan). It takes discipline, but it can be done.