I agree with your conclusion. Unfortunatly your 'study' dosn't prove this;
Your time frame is too short. Given the meal you had, even if fasted, you could still be digesting/absorbing for a couple more hrs.
During the time frame I would not expect much change in rate glucongenisis to occur. Certanly nothing that a capillary sample would detect with much accuracy.
The meal was off mixed compostion.
I certanly would not expect to see a change in urinary protein content.
Its a valiant effort but even using varied biochem methods and calculations in labs its not a simple thing to get right.
Again, I believe your thesis to be correct! There is no arbitary number that needs to be set against the amount of protein that we can absorb from a feed. It's more a matter of 'time' than much else. There off course is a debate about the increase in protein balance that can occur from a single feeding or protein. Protein balance can indeed be at basline inspite of significant concentrations of cirulatory amino acids.