People who believe they have eaten a large meal feel less hungry for hours after the meal, irrespective of the actual amount they consume, say researchers.
The study – published in PLoS One – suggests that people who think they have eaten a large meal have increased feelings of satiety for several hours after consumption of the food.
Led by Jeffrey Brunstrom from the University of Bristol, UK, the research team showed volunteers either a small or large portion of soup just before lunch, but then manipulated the actual amount of soup they consumed by means of a covert pump that could refill or empty a soup bowl without the eater noticing.
The team found that the level of hunger reported by the volunteers was proportionate to the amount of food they had eaten immediately after they ate, however 2 to 3 hours after lunch, volunteers who had been shown a larger portion of soup reported significantly less hunger than those who had seen the smaller portion.
Brunstrom and his colleagues said their results demonstrate the independent contribution of memory processes to feelings of satiety after a meal.
"This study is exciting because it exposes a role for cognition in the control of hunger - appetite isn't governed solely by the physical size and composition of the meals we consume,” said Burnstrom.
"Opportunities exist to capitalise on this finding to reduce energy intake in humans,” the researchers suggested.
The authors noted that while certain studies have suggested psychological and neurobiological evidence to implicate memory processes in the control of hunger and food intake, it currently remains unclear whether ‘memory for recent eating’ plays a significant role in neurologically intact humans.
“Before lunch, half of our volunteers were shown 300 ml of soup and half were shown 500 ml,” explained the researchers, who added that after this half of the volunteers consumed 300 ml while the other half consumed 500 ml.
“This process yielded four separate groups (25 volunteers in each),” they noted – those who had seen a 300ml package and consumed 300ml, those who had seen 300ml but consumed 500ml, those who had seen a 500ml product and consumed that amount, and finally those who had been shown the 500ml product but were given the 300ml product.
Immediately after lunch, the team found that self-reported hunger was influenced by the actual, and not the perceived amount of soup consumed. However, two and three hours after the meal this pattern was reversed.
“Hunger was predicted by the perceived amount and not the actual amount,” said the team. “Participants who thought they had consumed the larger 500-ml portion reported significantly less hunger.”
This was also associated with an increase in the ‘expected satiation’ of the soup 24-hours later, said the researchers, noting that more of these volunteers who had seen the bigger portions believed that the portion of soup they had consumed would satiate their hunger.
“For the first time, this manipulation exposes the independent and important contribution of memory processes to satiety,” said Brunstrom and his team.
“This raises important questions about our own diet and the use of fat substitutes and artificial sweeteners in many manufactured foods,” they added. “The prospect that these foods disrupt our memory for recent eating warrants attention and this represents a natural extension of the work that we present here.”
Source: PLoS One
Published online ahead of print, doi: 10.1371/journal.pone.0050707
“Episodic Memory and Appetite Regulation in Humans”
Authors: Jeffrey M. Brunstrom, Jeremy F. Burn, Nicola R. Sell, Jane M. Collingwood, et al