[MJS]

Here's the story: My dad's hobby is bodybuilding. He takes a lot of supplement protein drinks. Lately he has taken to giving about 2 ounces of a chocolate whey protein drink to our dog every night in spite of my protests. My dog has chronic recurring stiffness/soreness in his rear legs and hips. The pads of his feet are also very sensitive and susceptible to bad cuts.
Lately his problems seem worse than usual and he is also very easily fatigued. He is only 5 years old, but acts a lot older.
My question is, how can I explain, to a non-macrobiotic person like my dad, that the drink is not helping and could be causing some of our dog's problems.
He knows about theobromine and how it is toxic in large enough quanities, but insists that such a small amount is harmless. I counter that substances accumulate in the blood. Also, our dog eats a mostly processed dog food diet with very little vegetable matter. It seems like the extremely yang quality of his diet would make it harder for him to discharge a toxin like theobromine.

Am I right to worry? Can anyone give me some facts to help convince my dad I am right?
Thanks for your help. Mara