An increased protein intake is one of the most common approaches to the dietary management of obesity. The authors analyze the issues related to protein requirement in normal-weight and obese subjects, to the use and to the usefulness of high-protein diets in the treatment of obesity. Caution with these diets is recommended in view of their only slight effect on weight and fat loss and owing to the scarce evidence of significant effects on satiety and energy intake. Furthermore, the risks of harmful outcomes may be correlated to an excessive protein intake. Moreover, these diets do not allow patients to adopt those nutritional behavior rules which are essential to maintain the weight and fat loss and, consequently, significantly reduce the cardiovascular and metabolic risks related to obesity.