The organism may survive to few weeks starvation. During acute illnesses, stores are rapidly consumed. Consequences of malnutrition are multiple, the most relevant being immunodeficiency and therefore infection risk. Prevalence of malnutrition is high during chronic diseases, cancer, disease of the nervous system and in acutely ill situations. In French hospitals, as in the world, this prevalence is observed in 20 to 60%; it is more than 50% in elderly population. Malnutrition increases morbidity, mortality, decreases quality of life and has therefore a high economical impact.