The synthesis of serotonin at CNS level is influenced by diet. Moreover, insulin resistance is associated with lower serotonin levels. Visceral obesity, strictly linked to hepatic steatosis is specifically associated with mild to severe somatic affective-depressive symptom clusters. Previous data support the view that depression involves serotonergic systems, reflecting low levels of urinary 5- hydroxy-3-indoleacetic acid (5-HIAA). The 24-h urinary excretion of 5-HIAA was evaluated in 76 dystimic/depressed, obese/overweight females, divided into two groups, i.e., on a hyper-caloric diet, associated with a life style characterized by leisure time sedentary behavior (LTSB, 35 women), or on a normo-caloric diet, assisted by program-based strategies aimed at promoting physical activity participation (PAP, 41 women). Beck Depression Inventory (BDI) was carried out to score the severity of dystimia/depression. Anthropometric measures, metabolic indices, severity of hepatic steatosis at sonography and HOMA were studied. Urinary levels of 5-HIAA in controls and PAP groups were comparable with a great overlap, while in the LTSB group the urinary excretion of 5-HIAA was significantly reduced in respect to that of the PAP group and obviously compared to that of the control group, 3.4±1.4 mg/L versus 6.2±2.7 mg/L and 6.4±2.6 mg/L, respectively, ANOVA test, P= 0.001. Among metabolic indices, cholesterol, HDL-cholesterol, triglycerides and uric acid were not able to predict urinary concentrations of 5-HIAA, which were not associated with hepatic steatosis; vice versa, ferritin levels, and mainly HOMA values, were independent predictors of the urinary excretion of 5-HIAA (β=0.235 and 0.45, respectively). Dystimia/depression severity was negatively predicted by urinary 5-HIAA levels in the sense that the highest BDI values were forecast by the lowest values of urinary 5-HIAA (β= -0.72).The importance of measuring the 24-h urinary excretion of 5-HIAA in follow-ups could rely on a method simultaneously mirroring the well-being status, the adherence to physical activity, which leads to improved insulin sensitivity, and the eating habits acquired by dystimic/depressed overweight/obese patients. In contrast, the significance of the urinary 5-HIAA is reduced in evaluating the severity of hepatic steatosis, likely because it is a structured process.