Hunger Is Based on Perception of Meal Size and Length of Time Between Meals

--by Julia Haskins

The Gist 

Hungry? It might all be in your head, depending on how large you recall your last meal being. The study "Episodic Memory and Appetite Regulation in Humans" shows that the hippocampus, the part of the brain that controls memory functions, plays as important a role in determining hunger levels as having actually eaten a meal.

In technical terms, hyperphagia, or increased appetite, is associated with amnesia. If we think we've taken part in a large, fulfilling meal, even the false knowledge keeps us full until our next one. 

The Expert Take 

Our memory encoding has the ability to change the way our bodies feel, and so how satiated we are. If a person believes he or she has just enjoyed a satisfying meal, the cravings for a future meal will not be as pronounced. The opposite occurs if the person does not believe he or she has been fulfilled. Two people can enjoy the exact same portion of food, but their perception of the size of the meal will predict how they feel later. 

"The prospect that memory plays an important role in the regulation of food intake is consistent with an emerging literature on 'memory for recent eating' in humans," the researchers said. "In a series of studies, [researchers] have shown that reminding people of a recent meal can decrease the amount that is consumed at a subsequent meal. This effect persists for several hours into the inter-meal interval and, importantly, it is evident only when memory of a very recent meal is recalled."

The study goes on to explain the phenomenon of impaired coding by referencing patients with retrograde amnesia. "Bilateral hippocampal damage is associated with hyperphagia—after eating one meal to fullness, an amnesic may go on to consume further meals and to report no memory for recent eating and little change in hunger." 

Source and Method

100 volunteers took part in the study at the University of Bristol. Volunteers were first shown containers of either 300ml or 500ml of soup. They were then divided into four groups: those who had seen 500ml but eaten 300ml and vice-versa, and those who had both seen and eaten the same amounts.

Soup was added to or removed from bowls using a covert peristaltic pump to manipulate what subjects thought they had consumed. The hunger that participants felt immediately after consuming a larger or smaller bowl of soup was parallel to the actual bowl size, but hours later, those who believed they'd eaten a larger bowl of soup reportedly felt more full. The same line of thinking continued, as nearly 24 hours later, those who had seen a larger portion of soup believed they were more satiated. During the inter-meal interval, those who had seen 500ml of soup were less hungry than those who had seen 300ml.

Appetite was assessed for three hours after the meal, and the expected satiation value of the soup was assessed about 24 hours later. Expected satiation was measured by participants matching photographs of food to the bowl of soup in front of them by choosing the picture of food that would fill them up as much as the bowl of soup they were seeing. 

The Takeaway

For those who are dieting, or just believe in the power of mindful consumption, this study shows that we have more control over our bodies than we realize, which could lead to better weight loss strategies. 

"Opportunities exist to capitalize on this finding to reduce energy intake in humans," the researchers said. Dr. Jeffrey M. Brunstrom of the University of Bristol adds, "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." 

Other Research

Suzanne Higgs, Eric Robertson, and Michelle Lee took the aforementioned study further by researching multiple factors that contribute to overeating in their study, "Learning and Memory Processes and Their Role in Eating: Implications for Limiting Food Intake in Overeaters." In addition to memory episodes, the researchers explored other culprits of overeating, including the significance of food cues in choosing what we consume.