This must be for me
Depressed people tend to eat alot of refined carbohydrates, which spurs a heavy release of insulin, insulin causes you to not piss so much.
Anorexica, I suppose fits this budget. I remember them being low on potassium, so maybe they would piss so much, to conserve it.
Insulin takes up other amino acids, thereby leaving the transporter molecule for tryptophan, to makes its way into the brain for serotonin production. Fat cells make gamma interferon, an inflammatory cytochine, that degrades trytophan, which could have been used for serotonin production. That doesn't mean loose all your fat, it means don't be having too much hanging around.