I notice that when I get paranoid about my weight creeping up and suddenly eat less for several days, my general mood improves considerably.... I wonder if the chemistry described in these (admittedly more extreme) experiments on rodents done by Lutter et al. is what is going on. The experiments deal with the orexin neuropeptides, which can stimulate food seeking activity in mice and decrease anxiety-like behaviors in helplessness and social defeat model of stress. (Decreased levels of orexin-A have been reported in the CSF of suicidal patients with major depressive disorder, supporting chronic social defeat stress as a model of major depression.) The title of the article is "Orexin Signaling Mediates the Antidepressant-Like Effect of Calorie Restriction" Here is the abstract:
During periods of reduced food availability, animals must respond with behavioral adaptations that promote survival. Despite the fact that many psychiatric syndromes include disordered eating patterns as a component of the illness, little is known about the neurobiology underlying behavioral changes induced by short-term calorie restriction. Presently, we demonstrate that 10 d of calorie restriction, corresponding to a 20–25% weight loss, causes a marked antidepressant-like response in two rodent models of depression and that this response is dependent on the hypothalamic neuropeptide orexin (hypocretin). Wild-type mice, but not mice lacking orexin, show longer latency to immobility and less total immobility in the forced swim test after calorie restriction. In the social defeat model of chronic stress, calorie restriction reverses the behavioral deficits seen in wild-type mice but not in orexin knock-out mice. Additionally, chronic social defeat stress induces a prolonged reduction in the expression of prepro-orexin mRNA via epigenetic modification of the orexin gene promoter, whereas calorie restriction enhances the activation of orexin cells after social defeat. Together, these data indicate that orexin plays an essential role in mediating reduced depression-like symptoms induced by calorie restriction.