Thanks for your contribution. I agree with you that diet alone does not cause PTSD, but rather that our stress reactions either to environmental triggers or stressful thoughts tend to produce an overreaction, when we are afflicted with a metabolic disorder, that can be treated nutritionally.
The criticism against nutritional therapy is often misinterpreted to mean that diet alone causes a mood disorders. As you rightly pointed out it is usually a combination of "stress-producing thought patterns" AND a metabolic disorder that causes us to overreact.
Thus yes, meditation and other forms of psychotherapy can reduce our overreactions, but generally if we do not deal with the underlying biochemical abnormalities first, the psychological forms of therapy will have no lasting effects.