I believe that it’s the mind. After all, much of how we feel (physically), how we view ourselves, how we motivate (or not) ourselves to achieve optimum ‘physical’ fitness, and our general approach to life is directed by our thoughts, our minds.
I recently produced a short documentary film on the benefits of strength and conditioning for female athletes, and while the primary focus was on the physical benefits, a very interesting (and expected) additional benefit was the building of mental strength, confidence and positive outlooks that came from this as well.
I could write much more on this subject, but will leave it with my simple answer that in my opinion, it’s the “mind” that is the first area to optimum fitness and health from a holistic point of view.
I hope that this helps.