The gastric tract may be the first site exposed to diet-related oxidative stress. After food intake, dietary iron such as (met)myoglobin, the pigment of meat, oxygen, and polyunsaturated lipids come into close contact. The main goal of this work is the in vitro investigation of lipid oxidation taking place in the gastric compartment and its inhibition by dietary polyphenols. Oil-in-water emulsions stabilized either by bovine serum albumin (BSA) or egg yolk phospholipids (PL) were designed to model the gastric content. The metmyoglobin-initiated lipid oxidation led to the accumulation of lipid-derived conjugated dienes and volatile aldehydes. These reactions were faster in the BSA model than in the PL model, highlighting the influence of the interfacial composition. Quercetin, rutin, (+)-catechin, caffeic acid, and chlorogenic acid proved to be better inhibitors than alpha-tocopherol and ascorbic acid. Emulsions as models of the gastric environment are valuable tools to study the stability of macro- and micronutrients.