How hungry we feel may depend on how much we think we've eaten, not on how much was actually on the plate, researchers suggest.
Several new studies have explored the link between the mind, perception, and various aspects of health. Medical News Today have, for example, covered research that tied physical fitness to the perception of one's own activity levels and a study suggesting that feelings of pain may often have more to do with the mind than the body.
A new study led by Dr. Steven Brown, of Sheffield Hallam University in the United Kingdom, now explores the way in which the mind may influence our states of hunger and fullness.
Previous research had already looked at the relationship between what we think about what we eat and how much of that food we are likely to consume.
For instance, an existing study led by Dr. Brown and team suggested that "expected satiety" - that is, how full you expect to be after a meal - plays a significant role in how full you will actually feel.
In the previous study, the researchers used fruit smoothies to test their hypothesis, influencing the participants to think that they had consumed either more or less "filling" beverages.
Now, Dr. Brown and team are building on this, and similar, research to learn more about if and how our mind influences how much we eat. This time around, however, they have used solid food to see if they can replicate previous findings.
"My latest work [...] introduc[es] a solid food, lengthening the time over which participants' responses were measured (4 hours so it would be more like the time between breakfast and lunch), adding a behavioural measure (how much people ate at lunch)," Dr. Brown told Medical News Today.
In the current study, Dr. Brown also investigates whether or not levels of the "hunger hormone" ghrelin, which helps to regulate our sensation of hunger, play a role in this equation.
He told us that taking blood samples from the participants allowed him and his team to "investigate whether any differences were related to participants' ghrelin response," making this "a far more comprehensive investigation."
Perception matters, not size
Twenty-six individuals participated in the study. On two different occasions, participants were served breakfast, and their feelings of hunger and satiety, as well as their behavior at the subsequent meals, were monitored throughout the day.
On the first occasion, the participants were told that they were eating a two-egg omelette, whereas on the second visit they were told that it was a four-egg omelette. However, both times they were served omelettes containing three eggs.
What the researchers found was that when people thought they had eaten a smaller breakfast, they reported feeling hungry after only 2 hours. They also ate more for lunch and had a larger calorie intake throughout the day than when they thought they'd had a larger breakfast.
"We were [...] 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," explains Dr. Brown.
Memory 'a better target for investigation'
The researchers also collected blood samples from the participants on the two occasions they worked with them. Dr. Brown and team were interested in analyzing the participants' ghrelin levels, and learning whether they had an important role to play in their sensations of hunger and satiety on those occasions.
"Having analysed [participants'] 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," Dr. Brown notes.
He suggests that this finding shows how the subjects' perceptions of the meal before consumption significantly influenced their subsequent state of hunger, as well as their food intake.
Dr. Brown told MNT that significant differences in the sensation of hunger were typically recorded 2 hours after the meal. However, he was surprised to find that even when no significant shift in the sensation of hunger was reported, the participants still consumed larger lunches if they recalled having a smaller breakfast.
"As it turned out, hunger was only significantly different at the 2 hour point [...] As such, what was perhaps surprising was that there was still an influence over how much food was consumed," he said.
"Even though participants did not report themselves as particularly less full or more hungry, they still consumed more at lunch (on average) and when calories were calculated for the day, they had not corrected for this difference," he told us.
He hopes that this, and further studies, could help to forge a noninvasive pathway for improving people's well-being and dietary habits. As Dr. Brown explained to MNT, "The end goal of this type of research is to find ways in which we can influence people's behaviour in a positive way without having to interfere with day-to-day living."
Dr. Brown also believes that further studies on how our hunger mechanisms work should begin to focus on our minds, rather than our bodies.
"[M]emory 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."
Something else that he would like to explore in the future would be the perception of other types of food than the ones targeted so far. He wonders "what the response is to other macronutrients," and also whether the influence of perception over hunger can "be maintained over a length of time (e.g. at least a month)."
"If people were to learn after four or five occasions that, despite their expectations, they were not fuller when they thought that they would be, you would see the data converge," he explained.