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 hr 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.
Alex’s Notes: The eating environment is always interesting. How subtle things around us can influence how and how much we eat is fascinating work. While the title of this study already gives away the bottom line, it is still worth looking at to explore how meal size effects bite size, eating rate, meal duration, and deceleration rate.
Thirty-seven healthy women aged 18–60 (avg. 43) years with a BMI between 25 and 35 (average 29) kg/m2 were recruited to participate. Only women were chosen because of differences in eating behavior between men and women.To avoid alterations in normal eating behavior due to knowledge of the true study aims, the study was advertised as “investigating the influence of the eating environment on meal satisfaction”.
The participants attended five study visits (each separated by 2-20 days) at lunchtime between 11:30 am and 2:30 pm, standardized for each individual and following a 3 h fast. The experimental conditions consisted of five different portion sizes of a main meal presented in random order.They were asked to consume their usual breakfast at home at the same time on each study day, to avoid alcohol, and to keep evening meals and activity levels similar the morning of and the day before each visit. Upon arrival they completed pre-meal appetite ratings and then presented with one of the portions of the test meal and asked to consume it in full. They could take as much time to eat it as necessary and immediately after eating, the participants completed another set of appetite questionnaires.
The lunch meal consisted of chili-con-carne sauce with rice, provided in portion sizes of 229, 303, 400, 529, or 700 grams, with the ration of sauce to rice remaining constant.The largest and smallest portions represented a 75% increase, and a 43% decrease, respectively from the average portion of a chili-con-carne main course (400 g). That 75% increase appeared to be a little too much for some of the women, as three left more than 100g (15%) of the meal in the largest portion condition, and a fourth subject left more than 30% (351 g).
Be Damned Title that Gives Away the Punch Line
Overall, for every 100g increase in portion size, bite size increased by 0.22g, meal duration by 22.5%, and deceleration rate by 20%. On the other hand, eating rate only increased with portion size up to about 540g, after which point it decreased.
At first look, 0.22g doesn’t seem like a huge increase in bite size. However, this actually represented a 2-3% increase above the average bite size observed in our study (8-9g); and a 3-4% increase of a typical bite size reported in the literature (5-8g). Regarding the observations in eating rate, the authors suggest that portion sizes greater than 540 g are particularly large (35% larger than the national reference portion), and since the participants were required to consume the full portion, this may have encouraged them to artificially ‘pace’ their eating rate throughout the meal, relative to a more naturalistic context. Conversely, the speed of eating was more consistent (i.e. did not decrease so quickly) with larger portions, and the authors suggest that it is plausible that deceleration may be related to a priming effect of the food that is left on the plate, whereby the participants took longer to slow down their eating speed with larger portion sizes because they continued to be exposed to a large quantity of food for longer relative to the smaller portion size conditions.Therefore they maintained their initial eating speed for longer in an attempt to finish the meal more quickly to satisfy a pre-defined hunger goal.
There, so despite the title giving away the bottom line, hopefully there was still some information to be learned from digging in a little more. Notably that this was a controlled experimental study in overweight women and the results may not be generalizable to other groups and free-living conditions where the participants are eating freely.