MRC Elsie Widdowson Laboratory

Findings from the Eating environment and meal satisfaction study

Study purpose

The environment in which food is eaten may affect how much we eat and the way we consume the food. An important environmental factor to this respect is the amount of food that is placed on our plate (portion size). This study looked at how being exposed to different portion sizes of the same food affects the way in which we eat a meal. The main purpose was to investigate the way in which small and large portion sizes affect how much food is loaded on the fork (known as bite size); how fast the food is eaten (known as eating speed); how the eating speed changes over the course of the meal (known as deceleration rate); and the overall duration of the meal. Because knowing this information beforehand can unconsciously affect the way in which we eat, the participants in our study were initially informed that the study was investigating the relationship between eating environment and meal satisfaction, but were debriefed of the true purpose of the study at the end of the last session.

Participants

A total of 37 overweight women took part and completed the study between June 2012 and February 2014 in Cambridge. The mean age of the group was 44 (± 11) years and the mean body mass index was 29 (± 3) kg/m2. The majority reported being of White ethnic background.

Method

eating stationParticipants attended a training session followed by five lunch sessions at the MRC Human Nutrition Research to consume a meal and complete a number of brief questionnaires. On arrival participants were asked to drink a glass of water and complete a questionnaire on the computer asking about their hunger and fullness levels. Participants were then served a lunch made of a single course of chilli-con-carne with rice while seated at the eating station (depicted right).
The portion size of the chilli-con-carne meal varied between 229 g (about 8 ounces) and 700 g (about 24 ounces) and provided between 300 and 900 calories (depicted below).

chilliAfter completing the meal participants filled in a third questionnaire asking about their enjoyment of the meal and their hunger and fullness levels again. On the last study visit participants filled in an additional questionnaire asking about their eating habits and were debriefed about the main purpose of the study.

Study findings

Participants ate differently when exposed to the larger compared with the smaller portions of the chilli-con-carne meal. Specifically, participants loaded more food on their fork, ate faster, and continued to eat at the same speed for longer, when served the larger portions, compared with the smaller ones. So compared with the smallest portion of 229 g, the average bite size increased by 0.22 g for every 100 g increase in portion size, and the change in speed of eating (deceleration rate) went down by 20%. In other words, participants continued to eat quicker for longer and put more on their fork at each bite with the larger portions. Participants also took longer in finishing the largest meal compared with the smallest one (11 vs. 4 min on average).

The smallest portion size corresponded to about half of a standard portion size (a standard portion size is what is normally included in a commercial ready meal); while the largest study portion represented 75% more than the standard portion. This study showed that varying the portion size within this range affects the way in which we eat the food, in particular the speed of eating. Related research[1] has shown that we tend to eat more energy when we eat faster. Taken together these results suggest that larger portion sizes have the potential to make us eat more by altering the amount of food we load on our fork and how fast we eat it. Interestingly we did not observe a marked increase in hunger after the smaller portion sizes, and we also know that reducing the speed of eating does not increase hunger necessarily1. We can conclude then that strategies leading to portion control via a reduction in eating rate could be sustainable and help individuals eat less in the face of large portions.

Conclusions

This study showed that being exposed to large portions makes us eat quicker and load more on our fork. The changes in the speed of eating and amount loaded on the fork may explain why large portion sizes lead to increased energy intakes. While excessive portion sizes persist in the environment, strategies to reduce how much we load on our fork and that reduce the speed of eating may provide individuals with coping strategies to reduce the risk of overeating.

Additional information:

The results of the study have been published in the journal Physiology and Behaviour and are accessible at:

http://www.sciencedirect.com/science/article/pii/S0031938414005599.

[1] Robinson E, Almiron-Roig E, Rutters F et al. A systematic review and meta-analysis examining the effect of eating rate on energy intake and hunger American Journal of Clinical Nutrition, 2014. 100: p. 123-151.