Memories about how satisfying previous meals were also played a causal role in determining how long they staved off hunger. Together, these results suggest that memory and learning play an important role in governing our appetite.
In the first experiment, participants were shown the ingredients of a fruit smoothie. Half were shown a small portion of fruit and half were shown a large portion. They were then asked to assess the ‘expected satiety’ of the smoothie and to provide ratings before and three hours after consumption. Participants who were shown the large portion of fruit reported significantly greater fullness, even though all participants were given the same quantity of fruit.
In a second experiment, researchers manipulated the 'actual' and 'perceived' amount of soup that people thought that they had consumed. Using a soup bowl connected to a hidden pump beneath the bowl, the amount of soup in the bowl was increased or decreased as participants ate, without their knowledge. Three hours after the meal, it was the perceived (remembered) amount of soup in the bowl and not the actual amount of soup consumed that predicted post-meal hunger and fullness ratings.
The findings, which will be presented by researchers from the University of Bristol at this month’s annual conference of the Society for the Study of Ingestive Behaviour (SSIB), could have implications for more effective labelling of diet foods.
“The extent to which a food can alleviate hunger is not determined solely by its physical size, energy content, and so on. Instead, it is influenced by prior experience with a food, which affects our beliefs and expectations about satiation. This has an immediate effect on the portion sizes that we select and an effect on the hunger that we experience after eating,” said Dr Jeff Brunstrom, Reader in Behavioural Nutrition at Bristol university’s Department of Experimental Psychology.
“Labels on ‘light’ and ‘diet’ foods might lead us to think we will not be satisfied by such foods, possibly leading us to eat more afterwards,” added Dr Brunstrom. “One way to militate against this, and indeed accentuate potential satiety effects, might be to emphasise the satiating properties of a food using labels such as ‘satisfying’ or ‘hunger relieving’.”
The research was funded by the Biotechnology & Biological Sciences Research Council (BBSRC) through its Diet and Health Research Industry Club (DRINC) - a public-private partnership that funds research into how the UK food industry can help towards healthier diets and address serious public health issues such as obesity, as well as investigating the benefits of bioactive ingredients in food.