Objective Larger food portions lead to increased intake but the mechanism behind this effect is unclear. We investigated the effect of portion size on bite size, eating rate, deceleration rate, and meal duration. Design and methods Thirty-seven overweight women attended 5 visits after a 3 h fast and consumed a 229, 303, 400, 529 or 700 g portion of a lunch meal in random order. Meal eating parameters were measured with the Sussex Ingestion Pattern Monitor. Data were analyzed with mixed effects models. Results Average bite size increased by 0.22 g for every 100 g increase in portion size (p = 0.001); portion size had a non-linear effect on eating rate, increasing with portion sizes up to about 540 g (p = 0.01). Deceleration rate (reduction in speed of eating) decreased by 20% (p < 0.001) and meal duration increased by 22.5% for every 100 g increase in portion size (p < 0.001), relative to the smallest portion. Conclusions Increasing portion size led to a larger bite size and faster eating rate, but a slower reduction in eating speed during the meal. These changes may underlie greater energy intakes with exposure to large portions. Interventions to reduce bite size and slow eating rate may provide individuals with strategies to reduce the risk of overconsumption
