Digestion and Absorption of Tube‐Feeding Emulsions With Different Droplet Sizes and Compositions in the Rat

Assimilation of lipid nutrients depends on the efficiency of emulsified fat hydrolysis by digestive lipases. As shown in vitro, the activity of preduodenal and pancreatic lipases is governed by the physicochemical properties of emulsions. Thus the aim of this study was to evaluate in the rat how emulsions are digested and assimilated depending on their droplet size or solute composition. Fasted rats were intragastrically tube fed emulsions with different median droplet sizes (0.6 μm, fine; 22 μm, coarse) or solute composition (0.8 μm, complex fine) containing 14 C‐triolein and 3 H‐cholesterol. Two and 5 hours after feeding, fat‐droplet size was measured in gastric and duodenal contents, and lipids were radioactively quantified in different compartments. In the stomach, the droplet size of the fine emulsions significantly increased to values (13 μm to 24 μm) comparable with those of the coarse emulsion (35 μm to 36 μm). In the duodenum, the droplet sizes of the three emulsions were in the range of 14 μm to 33 μm. After 2 hours, gastric triglyceride hydrolysis was significantly higher with the fine than with the coarse emulsion and was lower with the complex fine emulsion. Gastric emptying of fat was significantly different, with the following decreasing order: coarse, fine, and complex fine emulsion. In the small intestine, the fine and coarse emulsions were processed comparably, whereas the assimilation of the fine complex emulsion was significantly delayed. Calculations indicate that ingested fatty acids were distributed in the peripheral tissues at different rates with the same decreasing order. The fate of a lipophilic nutrient, cholesterol, was also markedly altered by the type of emulsion. These data support the concept that tube‐fed emulsions with different droplet sizes and solute composition are digested differently and thus are metabolized differently. ( Jourual of Parenteral and Enteral Nutrition 18: 534–543, 1994)