Malnutrition and sarcopenia are consequences of life-threatening gastroenterological diseases such as liver cirrhosis, chronic pancreatitis and short bowel syndrome and are associated with a poorer clinical outcome and a reduced quality of life. The diagnostic criteria of both conditions differ, as do the consequences for adequate nutritional therapy. Nevertheless, malnutrition and sarcopenia are often discussed in confusion in the literature. In addition, the underlying mechanisms of malnutrition and sarcopenia can differ in the various diseases. The aim of the study is to compare nutrition-associated parameters from patients with liver cirrhosis, chronic pancreatitis and short bowel syndrome, to characterize the disease-specific phenotype of malnutrition and sarcopenia of the examined diseases and to obtain information on mechanistic relationships. The pathophysiological understanding of the clinical settings as well as the development of malnutrition and sarcopenia is important for choosing specific nutritional therapies. For this, malnourished and non-malnourished patients of each examined disease are compared with controls from patients with non-specific, abdominal symptoms and healthy control subjects. Data on food intake, physical activity, body composition and anthropometry as well as muscle strength and muscle function are recorded. Clinical and chemical blood parameters, the plasma metabolome as well as transport and barrier proteins of the intestine are also examined.