New research, published in the American Journal of Clinical Nutrition, highlights the benefits of the food industry changing food product portion sizes in order to make healthier eating more normal.

Historical increases in the portion sizes of commercially available food products are known to cause 'passive' overeating and have been linked to the emergence of the worldwide obesity crisis. One idea that public health bodies are currently promoting is that the food industry needs to reduce the portion sizes of the products they are selling.

Research from the University's Institute of Psychology, Health and Society, led by Dr Eric Robinson, aimed to establish whether reducing a food portion size "renormalizes" perceptions of what constitutes a normal amount of that food to eat and results in people selecting and consuming smaller portions of that food in the future.

Experiments

During the first of three experiments participants were randomly served either larger or smaller portions of the same meal (quiche and salad). The participants were advised the experiments were part of a 'food, mood, and reasoning' study as to not alert them to the real aim of the experiment which could have a detrimental effect.

During the second experiment, which took place the following day, participants were advised they could serve themselves whatever they wanted to eat from the same type of food provided in the first experiment.

In the third experiment, the participants were asked what their preferred portion size of the food was a week later.

The results from all three experiments showed that being served a smaller portion of food resulted in participants changing their perception of what a normal portion size was and this resulted in participants choosing to eat less food in future.

Recalibrating perceptions

Dr Eric Robinson, said: "There have been suggestions that shrinking the portion size of commercially available food products could be one approach to reducing overconsumption and tackling population-level obesity.

"The present findings indicate that if portion sizes of commercially available foods were reduced, these smaller, more appropriate portion sizes may recalibrate perceptions of what constitutes a "normal" amount of food to eat and, in doing so, decrease how much consumers choose to eat."

Dr Inge Kersbergen, said: "It is unclear from our research how long the effect would last for. The effects we observed were larger when we examined food intake the next day in the laboratory than when we looked at portion size preference one week later.

"Based on the idea that our immediate environment influences our perceptions of what a normal portion size is, it is likely that the effect would only last if we encounter smaller portion sizes more often than supersized portions."