The portion size you get served strongly determines how much you eat

More children are becoming overweight worldwide. For example, in the Netherlands, about one out of eight children in the age-group of 0-9 years is overweight. Being overweight is not only caused by not getting enough exercise on a daily basis, but also an important reason is that we have gotten used to eating bigger portion sizes of particularly energydense food. Numerous studies have shown it again and again: larger portion sizes, serving devices and packages lead people to eat more, often without them realizing it. In the last decades, the portion sizes of many, often relatively unhealthy foods increased. An example is the family bottle size Coca-Cola that was introduced in the Netherlands in 1954 which contained 0.75 litres. Now a family bottle size contains double this volume or even 2 litres. This portion size phenomenon can also be observed in slices of cheese, potato chips and chocolate bars. Consumers traditionally want ‘value for money’ and food companies and restaurants have appealed to these wants by providing larger portion sizes over the years. Unfortunately, as human beings, we are not good at recognizing feelings of fullness in the stomach and determining appropriate portion sizes accordingly. More than 90% of what people serve themselves is eaten. Research has also shown that people usually do not compensate for the increased intake by eating less later on in the day. As a result, scientists agree that this so-called ‘portion size effect’ is a large driver of the overweight problem globally.

Using the portion size effect ‘for the good’

But what if we use this ‘portion size effect’ to encourage children to eat more vegetables? Vegetables contain vitamins, fibre and are naturally ‘light’, but most children, like many adults, do not eat enough of them. The question is: do children unknowingly eat more when served more or do they stop eating? These questions were, in short, the reason for the ‘cucumber study’ in which 255 children of two primary schools in the Netherlands participated. The study was conducted by Ilse Bruggers, Emely de Vet and Ellen van Kleef of Wageningen University.
Getting children to eat more snack vegetables In this study, we investigated whether portion size could be exploited to entice children to eat more snack vegetables. Cucumber was chosen as a generally familiar and well-liked vegetable among children. We expected consumption in children to increase when portions are doubled. We served children (aged 8-13) cucumber during the morning break and presented the study to them as a taste test. Each class got the cucumber in a different way. In some classes, each child got two third of one cucumber and in other classes they were only served one third of a cucumber. We also varied the size of the pieces of cucumber; some were given small slices and others an unsliced piece. Children ate as much or as little as they wanted and filled in a questionnaire. Leftover cucumber was weighted afterwards to calculate the grams of cucumber eaten. All children participated enthusiastically in the study. ‘It was delicious and fun to do! Can you come back with strawberries next time?’ a 9-year-old girl wrote on the questionnaire.

Offering larger vegetable portions, preferably in smaller pieces

On average, children ate 115 grams of cucumber. Interestingly, children ate 54% more cucumber when served a large portion compared to a smaller portion. As such, intake of cucumber increased with 49 grams to about 139 grams, which represents about two-thirds of the recommended daily intake of vegetables in the Netherlands of 150 to 200 grams. Pre-slicing the cucumber did not influence how much children ate. Smaller sizes were, however, considered to be more convenient to eat.

The present study has some implications for the development of nutritional advice and interventions to encourage consumption of fruit and vegetables. The key message is to offer larger portions, preferably cut in smaller pieces. For example, presenting children with larger bowls of cucumber, carrots or other raw vegetables and fruit could encourage greater consumption. In this way, children will eat more without verbal encouragement or ‘pushing’ them to eat.

Based on: Van Kleef, E., Bruggers, I, and De Vet, E. (2015). Encouraging vegetable intake as a snack among children: The influence of portion and unit size. Public
Health Nutrition, 18(5), 2736-2741.