These results are complementary to data obtained in elderly humans showing a positive effect of the pulse protein feeding pattern on nitrogen balance (5). (academic.oup.com)
There's no reason to reduce the amount of protein you feed your older dog as long as he doesn't have any kidney problems. (dogfoodinsider.com)
Since the idea that protein is bad for your kidneys, liver, bones, etc. they also conducted a basic metabolic panel to track changes over the high protein feeding study. (sciencedrivennutrition.com)