It all depends who is taking Kuvan. Everyone responds differently to Kuvan. Some people respond alot, some respond a little bit, and some do not respond at all.
I did respond to Kuvan. When I started Kuvan I was allowed 300 mg of phe each day. After I began taking Kuvan my levels dropped so low that we had to add phe into my diet in order to keep my levels in a safe range. I am now up to 1000 mg of phe a day. This still really is not a high enough tolerance to eat meat on a regular basis. I do eat foods such as regular bread and tortillas, but besides that I have not tried a lot of foods. I personally have no interest in trying most foods. Surprisingly I like the low protein stuff better.
This is how I responded to Kuvan, but like I said everyone responds differently. The only way you will know is by trying Kuvan, which obviously is not yet an option for you. Hopefully Kuvan will come your way in the near future.