Although a great number of studies have been carried out on the relationship between chronic obstructive pulmonary disease (COPD) and low body weight, the identification of the most suitable warning signs of this wasting condition is still under debate. It has been indicated in earlier studies that body weight alone is of limited diagnostic value concerning this clinical condition in as far as a great number of COPD patients are usually overweight. For this reason, the aim of the current research was to find parameters that take into consideration the fact that body composition should be taken into account instead of weight only, and to assess whether COPD can be considered a "protein wasting disease", defining sensitive and significant indices of lean tissue depletion in relationship to the severity of the clinical symptoms. One hundred and seventy-five stable COPD outpatients with differing degrees of bronchial obstruction and arterial blood gas abnormalities were consecutively recruited: anthropometric measurements and body composition analysis were carried out; 60 healthy subjects with normal pulmonary function, matched for sex, age and anthropometric parameters, were considered as controls. The data obtained showed a lower prevalence (9%) of underweight COPD patients in comparison with normal weight (37%) and overweight (54%) patients. In COPD patients, the phase angle measured by bioelectrical impedance analysis, whose deterioration is a good indicator of protein mass depletion, was altered by 19%, thus allowing the identification of currently malnourished subjects included in the overweight COPD patients group. In addition, significant correlations (p = 0.000) were found between the same nutritional variable, respiratory function and gas-exchange parameters, thus confirming that the more severe the stage of the pulmonary disease, the higher the degree of protein breakdown, regardless of body weight.