Abstract Background Cancer cachexia (CCx) is a complex and multi‐organ wasting syndrome characterized by substantial weight loss and poor prognosis. An improved understanding of the mechanisms involved in the onset and progression of cancer cachexia is essential. How microRNAs contribute to the clinical manifestation and progression of CCx remains elusive. The aim of this study was to identify specific miRNAs related to organ‐specific CCx and explore their functional role in humans. Methods miRNA patterns in serum and in cachexia target organs (liver, muscle and adipose tissue) from weight stable (N ≤ 12) and cachectic patients (N ≤ 23) with gastrointestinal cancer were analysed. As a first step, a miRNA array (158 miRNAs) was performed in pooled serum samples. Identified miRNAs were validated in serum and corresponding tissue samples. Using in silico prediction, related genes were identified and evaluated. The findings were confirmed in vitro by siRNA knock‐down experiments in human visceral preadipocytes and C2C12 myoblast cells and consecutive gene expression analyses. Results Validating the results of the array, a 2‐fold down‐regulation of miR‐122‐5p (P = 0.0396) and a 4.5‐fold down‐regulation of miR‐194‐5p (P