Prospective single arm, single center observational study to assess the nutritional status and the nutrient supply during hospitalization for elective gastrointestinal surgery.

Inclusion Criteria:

• patients undergoing elective surgery of the upper or lower gastrointestinal tract
• mental and verbal ability to understand, read and write in German language
• written informed consent for study participation

Exclusion Criteria:

• age <18 years
• inadequate ability to be compliant with the study protocol or to complete documentation for the Food frequency questionnaires

Elective surgical patients