Recommended serving size leads to reduced consumption

Larger portions and packages are an important cause of the increase in the number of people with overweight and obesity. How can this portion size effect be prevented? Behavioural economist Iris Versluis conducted research on a number of measures for her thesis. Among others, it emerged that placing an image of the recommended serving size on the packaging had the desired effect. Versluis will obtain her doctorate on Thursday, 21 April 2016 at Erasmus University Rotterdam.

People have the tendency to eat more if they are served food in larger portions or packages, which is often referred to as the portion size effect. A notable feature of this phenomenon is that people will even eat more if serving sizes are so large that they wouldn’t be able to eat the smaller portion, let alone the larger one. This is why the trend towards increasingly larger portions and packages is considered to be an important cause of the growing number of people with overweight and obesity.

The first thing Iris Versluis set out to do for her thesis was to better understand the portion size effect. According to her, one of the reasons why this effect occurs is because the portion size gives an indication of what would be the proper amount to eat. It is a social norm. People are reluctant to be seen as overeaters and clearing one’s plate is seldom viewed as overeating. The result? The larger the serving, the greater the amount eaten.

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But Versluis also wanted to find ways to prevent the influence of the portion size effect. To do this, she conducted a series of experiments where test subjects were exposed to large or small serving sizes of various snacks.
Versluis concluded that reducing the influence of portion size and package size is difficult, but not impossible. People have the ability to control themselves, but they need a little help. They have to be encouraged in different ways to not base their eating behaviour on the serving size presented or to do so to a lesser extent.

One way to do this is to place an image of the recommended serving size on the packaging. This recommendation provides a good indication of what is the proper amount to eat and encourages people to moderate their consumption. In her experiments, Versluis exposed participants to snacks in packaging where some packages displayed the recommended serving size while others did not. As expected, the test subjects that saw a package featuring the recommended serving size wanted to eat less, but what was also significant was that the recommendation only appeared to be effective if presented in the form of an image. If only the number of grams was given without a visual aid, people found it difficult to correctly determine the indicated amount.

Reminding people of their dieting goals is another way to reduce the influence of portions. It had already been established that people who regularly diet are better able to control their food consumption if they are reminded of their dieting goals. A diet reminder of some kind can also prevent the portion size effect. Participants who from time to time viewed dieting product advertisements while eating from a large bag of M&Ms ate noticeably less, thus neutralising the influence of the portion size.

Iris Versluis (1984) studied Economics at Erasmus School of Economics where she obtained her BA and MA diploma cum laude. 

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