Zinc has important effects on metabolism, and on the thermoregulation of obese individuals. The aim of our investigation was to evaluate the serum zinc levels in obese patients before and after severe hypocaloric diets and to evaluate its correlation with the body mass index (BMI). Patients followed a severe hypocaloric diet (737 Kcal) for 60 days. Serum Zn levels and BMI were evaluated. Zn levels in obese patients were significantly (p < 0.01) lower than in controls, whereas the BMI values were significantly greater. At the end a severe hypocaloric diet, serum Zn and BMI levels returned to normal values. Our data show a possible relationship of the serum Zn levels with the anabolic and catabolic mechanisms in obesity, although the exact metabolic role of this bio-element remains unclear.