Despite eating the same breakfast, made from the same ingredients, people consumed more calories throughout the day when they believed that one of the breakfasts was less substantial than the other.
The research, funded by the Rural and Environment Science and Analytical Services at the Rowett Institute, is the key finding of research led by Steven Brown from Sheffield Hallam University which is being presented today at the annual conference of the British Psychological Society's Division of Health Psychology.
Previous studies have investigated the link between how filling we expect liquids (e.g. drinks) or semi-solids (e.g. smoothies/soups) to be and people's subsequent feelings of hunger up to three hours later.
These initial expectations have also been shown to be an important determinant of how much people eat at a meal provided a short time later. The current research shows that a similar effect can be seen when using solid foods (i.e. an omelette) and that the influence of those expectations is still present after a longer period of time (four hours later and the total day's calorific intake).
A total of 26 participants took part. Over two visits, participants believed they were eating either a two or four egg omelette for breakfast. However, both of the omelettes actually contained three eggs.
When the participants believed that the omelette was smaller they reported themselves to be significantly hungrier after two hours, they consumed significantly more of a pasta lunch and, in total, consumed significantly more calories throughout the day than when the same participants believed that they were eating a larger omelette.
Steven Brown said, "Previous studies have shown that a person's expectations can have an impact on their subsequent feelings of hunger and fullness and, to a degree, their later calorie consumption. Our work builds on this with the introduction of solid food and measured people's subsequent consumption four hours later, a period of time more indicative of the gap between breakfast and lunch.
"We were also able to measure participants' consumption throughout the rest of the day and found that total intake was lower when participants believed that they had eaten a larger breakfast.
"As part of the study, we were able to take blood samples from participants throughout their visits. Having analysed levels of ghrelin, a known hunger hormone, our data also suggest that changes in reported hunger and the differences in later consumption are not due to a differences in participants' physical response to the food.
Therefore, memory for prior consumption, as opposed to physiological factors, may be a better target for investigating why expectations for a meal have an effect on subsequent feelings of hunger and calorie intake."
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