The extra calories are what's working. For a natural such as yourself taking far more protein than your body can process just puts an unnecessary strain on your kidneys.
To my knowledge there has yet to be a study that shows any evidence to prove kidney strain. There is one study, but it was done on dogs. And the canine in question already had kidney problems to begin with.
With humans, there is not a great amount of evidence-studies or otherwise- to prove this.