Hello,
The reason a low protien diet is recommended is cats with Hyperthyroid disease are also prone to kidney disease. Too much protein can affect the Kidneys and cause Kidney failure. It is not because of the Medication that you have to change the diet, but because of the Hyperthyroidism. To prevent this we keep the cats on a low Protein diet. Joan Jav917
http://thyroid.about.com/cs/catsdogspets/a/hyperthyroidcat.htm
Vet. Tech
I have been a Vet, Tech. for over 30+ years. Working with Large Cats as well as house cats