Benton,D., (2015) Critical reviews in food science and nutrition 55:988-1004 10.1080/10408398.2012.679980
OBJECTIVE: To explore the effect of portion size and associated factors on energy intake, and to outline the current gaps in knowledge.
DESIGN: Narrative review.
SETTING: Various.
PARTICIPANTS: Various.
MAIN OUTCOME MEASURES: Evidence that portion size has increased; compensatory changes in the diet; short-term response to portion size in adults; influence of unit bias (number of items available to be consumed); influence of expected satiety and satiation; impact of portion size in children; mechanisms.
RESULTS: There has been a trend for portion size to increase but this is not universally the case. The concern is that the supersizing of portions changes perceptions of ‘normal’ amounts to eat.
Various studies have investigated the influence of portion size on subsequent energy intake, but as this is influenced by many factors such as timing of meals, macronutrient composition, day of the week etc, there are many reasons to question the generality and interpretation of longer term studies under laboratory conditions.
Laboratory or controlled real-world studies have produced the fairly consistent finding that where participants are provided with larger portions, they consume more. However, these data require careful scrutiny as studies consider portion size in isolation which may exaggerate its role. A variety of different factors influence consumers’ response to portion size such as: ‘unit bias’ which encourages higher consumption when larger unit sizes are presented; the expected satiation of a food which reflects prior knowledge, learning and adaptation - some evidence suggests that high energy foods are expected to be less satiating.
There are fewer studies in children some with poor designs. Some data from the USA have shown that whereas average portion sizes consumed by under 2-year olds have not changed, the portion size of drinks for 2+ year olds has increased.
Mechanisms discussed include visual cues, size of packaging, labelling, plate size and perceived value for money. Labelling a food “low fat” or “organic” may lead to the assumption that it contains fewer calories and can be eaten in larger quantities. There is a presumption that using a smaller plate is beneficial but this has been the subject of little systematic study.
The single most important objective of future research is to establish the importance of portion size relative to the range of other variables that influence food intake. More free-living studies are needed with freely chosen diets in contrast to laboratory studies.
CONCLUSIONS: A multitude of factors impinge on what a person purchases/chooses/serves in terms of portion size. The interest in portion size reflects the increased incidence of obesity and will ultimately only prove to have value if it results in a practical and successful means of intervening. It will need to be demonstrated that interventions are beneficial in well-controlled long term trials. For example it needs to be established that the response to a description of a small portion size is not to increase consumption of that item, or another component of the meal.
Note to Readers: Any opinions expressed in the recent research abstracts are those of the authors of the original scientific papers and may not reflect the views of Sugar Nutrition UK