Is Poor Memory Bad for Your Waistline?
Exploring the intersection of cognitive processes and eating behavior.
Posted Sep 10, 2019
When asked what motivates eating, many would give an answer that generally resembles some sort of homeostatic model. The body can detect that it’s lacking nutrients, and thus it signals one to be hungry and consume food. Then as we eat, the body detects that too and sends a signal to stop eating. There is certainly a lot of evidence that this kind of feedback system exists in most animals and there have been tremendous advances in our understanding of the physiology and neural processes that govern this system.1 That said, many researchers have begun to question the efficacy of this model particularly as it pertains to obesity. That is, if we are wired to eat because we are lacking nutrients and stop when we obtain them, why do people overeat, eat when they’re not hungry, or eat when they’re not lacking nutrients? Clearly, there appear to be other factors at play that are causally related to eating.
One such factor that has gained traction of late is that memory is important for moderating eating. This idea was birthed from studying patients with severe amnesia. First, it was noted that their hunger levels were not well correlated with the time since their last meal. More strikingly, a patient could be served the exact same meal over and over again if spaced out properly, because they would forget the previous eating event.2 This suggested that the memory of one’s most recent eating event influences eating behavior at a subsequent meal. Similar patterns have been found in healthy adults using better controlled and more experimental methods. In these studies, some sort of manipulation is utilized to diminish the memory of an eating event, such as having participants watch TV or play video games while eating. As a result, their memory for how much food they consumed during the meal is worse compared to a control group that ate the same amount of food but not while being distracted. Moreover, in a snacking task several hours later, participants who had the poorer memory of eating, because of the distraction, end up eating more food.3 In a recent study, a team of researchers from Georgia State University used optogenetics, a neuroscientific tool that allows researchers to effectively turn on or off specific brain regions, to turn off memory-forming regions of the brain immediately after rats consumed a meal. In doing so, the rats were not able to fully form a memory of that eating event, and as a result, they initiated their next meal sooner and ate more at that meal than rats who ate the same first meal but had an intact memory.4,5
These findings are, of course, concerning, because many people, myself included, often eat our meals in front of a television or computer screen. In fact, we have an entire genre of food (i.e., TV dinners) dedicated to this style of eating. The empirical evidence strongly suggests that this kind of distracted eating can cause greater subsequent eating, which may be a contributor to obesity.
Related to this, it has long been known that obesity and memory deficits are highly intertwined. For instance, rats put on a so-called ‘junk food diet’ not only show a significant increase in weight gain, but also almost immediately show impairments in memory-related tasks.6 Conversely, rats with a lesion to the hippocampus, a brain structure critical to the formation of memories, will overeat and become obese compared to rats with sham lesions.7 This bidirectional relationship of memory processes and obesity is also evident in humans. Individuals with higher BMI (body mass index) demonstrate poorer episodic memory performance on certain tasks compared to individuals with normal BMIs8 and children and adults with obesity show reduced grey matter in brain areas pertinent to memory formation, such as the hippocampus and prefrontal cortex.9 It is, of course, important to note that this seemingly strong correlation between obesity and worsened memory performance provides a bit of a causal conundrum. Are individuals gaining weight because of their poorer memory abilities or is weight gain causing deficits in memory? While there appears to be stronger evidence that obesity causes these memory deficits, some have proposed that these two associations can work in tandem to create a vicious cycle of obesity and cognitive decline.10 According to this model, a Western diet and excessive food intake decreases hippocampal function, which, in turn, prevents memories of recent meals from adequately moderating current food consumption. This leads to excessive food intake, thus resulting in a vicious cycle.
So far, I’ve painted a somewhat bleak picture of our understanding of memory processes and eating behavior. To answer the question posed in the title, yes, it does seem that poorer memory is associated with increased weight gain, although the causal mechanisms that underlie this relationship are still unclear. That said, there are empirical demonstrations that illustrate ways of using this knowledge to our advantage. While, distracting participants as they eat reduces meal memories and causes greater subsequent eating, some manipulations that increase memory of a meal have been shown to reduce future food consumption. This includes instructing participants to focus on sensory aspects of their meals11 or by manipulating the food items so that participants are forced to chew for longer.12 Similarly, having participants simply recollect their most recent meal before initiating a subsequent meal has been shown to decrease consumption of that meal.13 Practically speaking then, if a person wishes to reduce how much they eat, they should strive to make their meals memorable. This includes cutting distractions while eating and could also include recording details of the food consumed at each meal and frequently consulting said records before initiating their next meal. Likewise, as the obesity epidemic continues to grow and burden society, identifying the factors that influence the formation of meal memories will be of critical importance and a worthy quest for researchers interested in both memory and eating behavior.
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2) Rozin, P., Dow, S., Moscovitch, M. & Rajaram, S. What Causes Humans to Begin and End a Meal? A Role for Memory for What Has Been Eaten, as Evidenced by a Study of Multiple Meal Eating in Amnesic Patients. Psychol. Sci. 9, 392–396 (1998)
3) Higgs, S. & Spetter, M. S. Cognitive Control of Eating: the Role of Memory in Appetite and Weight Gain. Curr. Obes. Rep. 7, 50–59 (2018).
4) Hannapel, R. et al. Postmeal optogenetic inhibition of dorsal or ventral hippocampal pyramidal neurons increases future intake. eNeuro. ENEURO.0457-18.2018 (2019). doi:10.1523/ENEURO.0457-18.2018
5) Seitz, B.M. Remembering to Eat: Inhibiting Hippocampal Neural Activity during the Postprandial Period Increases Future Food Intake. eNeuro Blog. (2019).
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10) Davidson, T. L., Sample, C. H. & Swithers, S. E. An application of Pavlovian principles to the problems of obesity and cognitive decline. Neurobiol. Learn. Mem. 108, 172–184 (2014).
11) Robinson, E., Kersbergen, I. & Higgs, S. Eating ‘attentively’ reduces later energy consumption in overweight and obese females. Br. J. Nutr. 112, 657–661 (2014).
12) Higgs, S. & Jones, A. Prolonged chewing at lunch decreases later snack intake. Appetite. 62, 91–95 (2013).
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