The clinical use of direct calorimetry for measuring energy expenditure.

Energy output measurements are an actual problem since the 18th century. Together with the technical development very good solutions for direct calorimetry are available. Vienna Whole Body Calorimeter is a measuring system in which man can live 24 and more hours under defined activity and well known diet. Utilisation of ingested food energy is discussed and unmeasured energy shown during overfeeding. Beside increasing energy content of body mass gaining weight costs 1969 kcal/kg. Comparison of direct and indirect measurement is necessary to define energy need in different catabolic situations.