I somewhat disagree with the diet/lifestyle advice for mental illness.
The only thing that diet can possibly change is the chemical aspect of mental illness. There are two theories of “mental illness”: one is chemical, one is neurological.
But I personally believe that mental illness is mostly neurological (electrical). Food (and psych pills which far more effectively alter the balance of the major chemicals that assist in transmission of neural signals) can not alter connections between neurons.
Some other things must be done to alter the neural connections. Something must be done to assist in the creation of new connections, suppression of the use of old connections.
We know in the case of schizophrenia that the actual physical problem is entirely neurological - there are missing brain connections. With other mental illnesses, the evidence for either chemical or neurological causes are hard to get. There are small pieces of evidence on either side.