Schizophrenia, Bipolar and the other conditions you mentioned have basically only corellational evidence for them being biologically based. And the research connecting them to early trauma is abundant. So if fasting is beneficial for those than it will be profoundly benefiical for PTSD. I think however that it would be misguided to assume that fasting will heal trauma alone. You definitely need to be doing emotional work and trauma healing during your fast.