An evaluation of unabsorbable markers in the study of fat absorption.

The validity of using water-soluble unabsorbable markers in the study of fat absorption was investigated. Nine subjects were fed a finely emulsified test meal containing carbohydrate, protein, fat, and the water-soluble unabsorbable markers, polyethylene glycol, and/or phenol red. The ratio of fat to marker in recovered gastric contents was significantly different from that in the test meal. This was due to the dissociation of the meal into two phases, a solid phase rich in fat and poor in marker and a liquid phase poor in fat and rich in marker. The liquid was preferentially emptied from the stomach and also more readily sampled by a small bore tube. When this artifact is disregarded samples obtained from the proximal small intestine would erroneously indicate an extensive and rapid absorption of fat in the duodenum and proximal jejunum.