Anorexia is a frequent and complex symptom occurring physiologically in older persons and during acute or chronic pathology. It's an adaptable physiological response to stress. It must be respected as such, as long as it's quickly reversible. The study of anorexia requires evaluation of oral intakes, causal aetiology and nutritional repercussion on body composition, different systems function and quality of life. Early artificial nutrition is recommended for adult patient who severely diminished oral intakes for 7 to 10 days after the beginning of acute pathology. Artificial nutrition is also indicated with chronic pathology associated with a significant weight loss. Faced to the impossibility of treating anorexia and its all causes, we have to treat at least anorexia repercussions and prevent undernutrition with an adequate artificial nutrition.