>My question is somewhat academic (somewhat practical, and somehat
>personally relevant - re: Mighty Mouse, who has been on a high protein
>(baby food supplemented) diet for insulinoma - last BG was 96 :), and has
>one failing kidney), but I am academically curious as well.  I know there
>is some "controversy" regarding low-protein diets and renal disease,
>albeit, I haven't researched the nature of the controversy.  My question
>is coming from what I have learned here at OSU.  I will be starting my
>GI/Urinary rotation next week, so this is coming from my 2nd year notes.
>
>What we learned is that while low protein diets can abate the signs of
>uremia, they do nothing to affect/slow the progression of renal disease.
>That being said, phosphorus itself *is* nephrotoxic, *and* it is usually
>found in high concentrations in high protein diets.  Therefore,
>indirectly, low protein diets would be beneficial in that they restrict
>phosphorus intake.
 
Dear X:
 
Let us progress from the fact that normal levels of phosphorus in the
normal kidney are not damaging (or we'd all die a lot sooner).  Evolution
has chosen a level of dietary phosphorus that we can handle, and has
adapted our kidneys to adjust.
 
Research in rats has shown that even doubling and in some cases,even
quadrupling the level of dietary phosphorus in rats with normal kidneys
will not cause any damage.  However, if you remove a kidney (approximately
50% of the renal function) or more (this is how researchers) damage to the
remaining kidney will be seen.  (The end result of this toxicity is the
deposition of calcium phosphorus salts in the kidney and death of affected
segments.)
 
The levels of phosphorus in high-protein diets are still not high enough
to cause a problem in the normal animal, so these diets, or those with
less phosphorus really will have little effect on a ferret who is not in
renal failure.  However, the animal in renal failure, who has less than
50% of functioning kidney left (actually probably less than 66% - which
is when we get our first inklings of renal damage in domestic species) is
more prone to damage from high levels of dietary phosphorus.
 
Hope that helps.
 
With kindest regards,
Bruce Williams, DVM
[Posted in FML issue 3576]