Objectives
This paper aims to study the features of colloidal species in the lumen of the upper small intestine of two healthy adults at fasted state by means of electron microscopy.

Methods
Samples were aspirated from a location near the ligament of Treitz 30 min (volunteer no. 1, Aspirate30min sample) and 60 min (volunteer no. 2, Aspirate60min sample), after administration of 240 ml of an aqueous solution in the fasted state.

Key findings
In the Aspirate30min sample micelles coexist with multi-, oligo- and unilamellar vesicles. Tubular structures and long structures were frequently visualised. In the Aspirate60min sample micelles, few unilamellar vesicles, long structures and tubular structures were the dominating structural features. In both samples, multivesicular structures and faceted vesicles (previously visualised at fed state) were absent. Structural features of both samples bear similarities with previously studied samples from the lower intestine in the fasted state. Micelles and unilamellar vesicles observed in both samples closely resemble morphological characteristics of those found in fluids simulating the colloidal species in fasted upper intestinal environment.

Conclusions
Features of colloidal species in contents of fasted small intestine have similarities with fluids simulating the contents in fasted upper small intestine and with contents of lower intestine in the fasted state.