He responded respectfully and apologetically. I don't think the concept of less fat not always being desirable quite permeated his bodybuilder worldview, but he seemed to get the part about different students having different priorities and the importance of his ability to recognize their goals and support them as an instructor, which is functionally what I wanted to accomplish. And he complimented the tone of the e-mail, which makes me feel good about my ability to employ tact when necessary. That's never been one of my strengths. :P