OBJECTIVE Weight loss improves the metabolic syndrome (MetS) features and related clinical abnormalities in obese subjects. The aim of this study was to assess the effects of a non-surgical therapeutic program on the MetS in severely obese patients. METHODS Sixty-four extremely obese patients were involved in the therapeutic program, which consisted of two alternating phases: the three-week therapeutic fasting or semi-fasting in hospital conditions and the low calorie diet with dosed physical activity in outpatient conditions. At the baseline we measured: anthropometric parameters, blood pressure and lipid profile. Subjects underwent an oral glucose tolerance test and insulin resistance/sensitivity was evaluated by the homeostasis model assessment and the oral glucose insulin sensitivity. After weight reduction by at least 10%, all mentioned assessments were repeated. RESULTS None of the patients had significant adverse effects. Forty-one patients aged 43.0±11.5 years completed the study. The mean weight loss was 27 kg or 18% of the initial weight (p<0.01), which was followed by a significant decrease of the insulin resistance, the overall prevalence of MetS (32%) and all MetS parameters, without the significant change in high-density lipoprotein. This weight loss pogram substantially improves the MetS in extremely obese patients. CONCLUSIONS The tailored alternating either fasting or semi- fasting should be considered as an optional approach to manage extreme obesity and related metabolic abnormality.