Abstract : Metabolic disorders, especially obesity, type 2 diabetes and metabolic syndrome, are frequently associated with depressive symptomatology, including severe depression. In fact, there is a two-way relationship : metabolic disorders could promote depression and depression could favour metabolic disorders, which may lead to a vicious circle. The reasons for this astonishing relationship are diverse : a genetic predisposition, shared biochemical abnormalities including low-grade inflammation, bad habits that combine unhealthy food and excessive sedentary life-style, poor therapeutic compliance. Medications that target metabolic disorders may positively impact depression, with recent promising, yet preliminary, data with glucagon-like peptide-1 receptor agonists. Moreover, antidepressants may also influence metabolic disorders, depending on the type of medications : their respective metabolic effects will be analyzed in a next article.