Portion size markings on snack packaging influence how much people eat

Men eat fewer crisps and women eat fewer chocolate biscuits when portion sizes are clearly marked on packaging, according to new research by the ESRI’s Behavioural Research Unit. The researchers conducted two controlled behavioural experiments to test this.

In both studies, funded by the Department of Health, representative samples of consumers received the same snacks but the packaging was varied at random. Half of the packs had portion size and nutritional information in a table, as normal. The other half had additional white stripes that marked out where one portion ended, and the next one began, with a label reading ‘1 portion’ between them. The food inside was not altered.  

People ate less of the snacks when portion sizes were marked by stripes on the outside of the packs, but the effects differed by gender. In the first study, which used cans of crisps served at a venue, men ate less. The effect was large, with a 33 per cent reduction in the number of men consuming more than the portion size recommended on the packaging.

In the second study, households received gift packs containing packets of chocolate biscuits and received a follow-up survey a few days later. Where a woman received the package, the portion size markings led to a 26 per cent drop in the number of households eating more than the recommended portion. Households with children were also less likely to open packs with portion size markings.

Two findings were consistent across both studies. First, the markings reduced consumption among people inclined to consume the most. Second, consumers were far more likely to notice the markings than the portion size written in the standard nutritional information table.

The research also found widespread confusion about where portion size information comes from. Many consumers believe it is a health recommendation from the government. In fact, portion sizes are determined by the manufacturer.

“Changes to the format of information can change how it is perceived”, said Dr. Deirdre Robertson, lead researcher on the study. “Displaying portion size information as highly visible stripes influenced how much attention consumers paid to it and how much they ate. Controlled experiments like these can provide objective evidence about how people understand, attend to and act on nutritional information.”

The research was funded as part of the Department of Health and the ESRI’s Research Programme in Healthcare Reform. It was informed by the Department of Health’s Obesity Policy and Action Plan, which recommends a suite of measures and cites portion size control as one method to implement as part of food product reformulation to help reduce levels of obesity.