I do sometimes sleep, actually.  On the subway back and forth from
work.

It would be surprising that protein concentrations did not vary
somewhat (perhaps not significantly) during a feeding, but I have
never heard of any studies that demonstrated this.  This may be why
you did not get any answers.

There are problems in measuring protein in biologic fluids.  Nitrogen
content was an early way protein content was measured and, I think,
still is sometimes measured.  However, there is up to 30% of nitrogen
in milk which is not in protein.  This leads to confusion and
incorrect results.

Jack Newman, MD, FRCPC