Hypothesis: Bile micelles are thought to mediate intestinal absorption, in part by providing a phase into which compounds can partition. Solubilizing capacity of bile micelles is enhanced during the digestion of fat rich food. We hypothesized that the intestinal digestion of triglycerides causes an increase in volume of micelles that can be quantitatively monitored over the course of digestion using small-angle neutron scattering (SANS), and that SANS can enable evaluation of the contribution of each of the components present during digestion to the size of micelles. Experiments: SANS was used to characterize the size and shape of micelles present prior to and during the in vitro simulated intestinal digestion of a model food-associated lipid, triolein. Findings: Pre-lipolysis mixtures of a bile salt and phospholipid simulating bile concentrations in fed conditions were organized in micelles with an average volume of 40 nm(3). During lipolysis, the micelle volume increased 2.5-fold over a 2-h digestion period due to growth in one direction as a result of insertion of monoglycerides and fatty acids. These efforts represent a basis for quantitative mechanistic understanding of changes in solubilizing capacity of the intestinal milieu upon ingestion of a fat-rich meal. (C) 2017 Elsevier Inc. All rights reserved.