[Nutrition alterations in internal medicine. Body composition analysis with bioelectrical impedance]

To determine the prevalence of malnutrition in patients in Internal Medicine. To describe the changes of corporal composition depending on body mass index (BMI). To evaluate validity of the different screening tools for the estimation of body composition.

Prospective observational cross-sectional study of the prevalence of malnutrition in 300 patients (sample 1); these were chosen 136 patients (sample 2), classifying in four groups: BMI < 20: 30 patients; BMI = 20-25: 46 patients; BMI = 25-30: 30 patients, and BMI > 30: 30 patients. In the patients of sample 2, we carried out a protocol of nutritional evaluation with anthropometry, laboratory and bioelectrical impedance analysis.

The prevalence of desnutrition was 9.3% and the obesity was 22.3%. In undernourished patients, the measure of body compartments with bioelectrical impedance, expressed in percentage of body weight, were: fat mass 20.5%, fat-free mass 79.4% and total body mater 58.3%. The body composition in obeses was: fat mass 40.1%, fat-free mass 60.6% and total body water 44.3%. The patients with normal BMI, the meta index (impedance at 50 kHz/BMI) was 25.9 +/- 5.21; in undernourished the index was higher (36.7) and obeses lower (15.5). The meta index (30-20) estimates desnutrition-obesity with high sensibility and specificity. The prevalence of desnutrition varies from 6% to 69% and obesity from 23% to 74%, using different methods and criterions for the estimation of body composition.

In Internal Medicine, the overweight (BMI > 25) is the most prevalent nutritional alteration. The bioelectrical impedance analysis helps for estimation of body composition and meta index is a very useful indicator of malnutrition (desnutrition-obesity).