11 Sep 2017 --- 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. This is the key finding of research, funded by the Rural and Environment Science and Analytical Services at the Rowett Institute, led by Steven Brown from Sheffield Hallam University. It was presented on 6 September at the annual conference of the British Psychological Society’s Division of Health Psychology.
Previous studies had investigated the link between how filling we expect liquids (for example, drinks) – or semi-solids (for example, smoothies or soups) to be, and people's feelings of hunger up to three hours later.
These initial expectations have also been shown to be an important factor in deciding 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 (in this case, an omelet) and that the influence of those expectations is still present after a longer period (four hours later and the total day's calorific intake).
“Many behaviors are accounted for by conscious, effortful actions (in the context of food, dieting would be an example),” study author Brown tells NutritionInsight of the future implications of the study. “However, more and more evidence suggests many decisions are driven by subconscious cues. We want to try and take advantage of those cues to help people maintain or lose weight without the potential consequences of the more effortful, conscious actions, that can actually have adverse and unforeseen consequences (e.g., dieting can lead to binge eating and weight gain) and often require conscious food restriction.”
Expectations lead to fuller feeling A total of 26 participants took part. Over two visits, participants believed they were eating either a two- or four-egg omelet for breakfast. However, both of the omelets contained three eggs.
When the participants believed that the omelet 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 omelet.
“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,” Brown says. “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,” Brown continues. “As part of the study, we were able to take blood samples from participants throughout their visits. Having analyzed 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.”
Brown believes that the results give a better impression of why expectations for a meal have an effect on hunger: “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.”
“There are other areas where this type of subconscious cue could influence eating behaviors, so there are a many interesting avenues,” Brown adds of potential future studies. “In terms of this particular research, some of the questions that remain are: [Firstly,] what is the response to other macronutrients? We used high protein (eggs) and high fat (cheese) in the omelet but what would happen if it was a high carb food, for example? My suspicion is that this could have an even greater effect as carbs tend to be less satiating than protein and, therefore, the response to them may be more open to psychological influence.”
“[Secondly,] do people learn over time?” Brown continues. “It needs to be demonstrated that expectations remain influential in terms of intake over a length of time (e.g. repeatedly for at least a month). If people were to learn after four or five occasions that, despite their expectations, they were not fuller or hungrier when they thought that they would be, you would see the data converge.”
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