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Background: Given the growing prevalence of overweight and obesity, weight-management strategies could be developed based on the effect of specific food ingredients on the gastrointestinal system to reduce food intake. Objective: The aim of this study was to investigate the mechanisms by which a vegetable-oil emulsion may exert its effect on satiety by applying a multilumen tube to investigate digestion and absorption of lipids in the stomach and proximal jejunum. Design: We gave 16 healthy, normal-weight subjects (in a doubleblind, placebo-controlled crossover design) a test product (yogurt with a vegetable-oil emulsion) or an equal-calorie control by intragastric administration on 2 separate occasions. Gastric and intestinal samples were collected from the proximal jejunum during 180 min. Results: We observed almost double amounts (P < 0.05) of total lipids, mainly as free fatty acids, from the test product (450 [+ or -] 119 mg) in the proximal jejunum compared with amounts of total lipids from the control product (230 [+ or -] 50 mg), and an over-time difference of free fatty acid concentrations was observed between the products (P < 0.05). To our knowledge, a novel and unexpected finding was the appearance of needle-shaped crystals in the jejunal samples that originated from the vegetable-oil emulsion and consisted of saturated fatty acids. Crystals were only rarely seen in the control samples. Conclusion: The higher amount of lipids in the proximal jejunum and the recovery of crystals in the intestinal samples after testproduct infusion provide a plausible physiologic explanation for the ileal brake mechanism that leads to the increased satiety observed for this test product. doi: 10.3945/ajcn.2009.28941