SCOPE: We have tested the hypothesis that high fat foods such as chocolate induce reduced rates of gastric emptying in comparison to lower fat foods and that this can impact uptake of allergens and subsequent reactions in allergic patients. METHODS AND RESULTS: In four volunteers, magnetic resonance imaging was used to measure gastric emptying of a series of nine doses of either dark chocolate bars containing 35% fat or a chocolate dessert containing 8% fat. Analysis showed a mean rate of decrease in gastric volume with an 8% fat dessert was 0.33 ± 0.09 mL/min compared to an average rate of increase in gastric volume of 0.09 ± 0.10 mL/min for the chocolate bars. In parallel, eight allergic patients were challenged for either peanut or hazelnut in the same two matrices and doses using a standardized protocol. A statistical analysis of the objective symptoms in the allergic patients showed that the chocolate bars gave a significantly higher threshold for objective symptoms than the dessert. CONCLUSIONS: Chocolate bars induced lower gastric emptying rates and in food challenges with allergic patients gave a higher threshold of elicitation for objective reactions than a dessert.