If I Don't Remember Eating It, I Didn't Eat It: Memory and Food Intake

Given the ubiquitousness of weight, obesity, and eating discussions these days, I thought I'd talk about some research that has, for some reason, stuck in my mind since I first heard about it a few years ago. It concerns the relationship between memory and eating. We all know that the desire to eat isn't just about the physiological condition of being hungry. Stress, depression, loneliness, and all sorts of other psychological states can make us want to eat more than we otherwise would. So it should come as no surprise that eating has "psychological" components. It may surprise you to learn, though, that memory may have a lot to do with how much you eat, too.

The study that always pops into my head at strange moments wasn't the first to look at the relationship between memory and eating (earlier studies had been done with the famous amnesiac HM1), but it is the most striking. Rozin et al.2 studied two patients with severe anterograde amnesia, who remembered almost nothing about things that had happend more than a minute before. That means that a minute or so after eating a meal, they would not remember having eaten it. Rozin et al. gave the two patients a large lunch (1000-1500 calories, if I remember correctly), and 10-30 minutes later, they gave them another lunch of the same size. Most of us would still be full, and wouldn't be able to eat the second lunch, but the two patients ate the whole meal. Then, after another 10-30 minutes had passed, they gave the two patients another meal, and again, they began to eat it. The experimenters stopped the experiment there, because they didn't want to hurt the patients, but the effect is still striking. Because they couldn't remember having eaten, they didn't feel full when the second and third meals were given to them, and ate them like they hadn't eaten in hours.

Since most of us don't have amnesia, the role of memory on hunger isn't quite as profound for us; and of course, because these patients had severe brain damage, it could be that there were physiological reasons unrelated to memory that were responsible the excess eating. So in order to look at the effects of memory on eating for those of us who have intact memory systems, Suzanne Higgs conducted a study with individuals who did not suffer from any brain damage3. In her first study, participants (all female) were given a full lunch in the lab, and after 2-4 hours, they were either asked to think about what they had for lunch or told to think about whatever they wanted (control condition), and then given what they were told was an unrelated cookie taste-testing task. The participants who had been asked to think about what they had for lunch ate fewer cookies than those in the control condition, indicating that remembering their previous meal decreased their desire to eat. In her second experiment, participants were given a full lunch, as in the first study, and after 2-4 hours they were asked to either think about that day's lunch (same-day condition), to think about what they'd had for lunch the previous day (previous-day condition), or to think about whatever they wanted (control condition). Participants in the same-day condition ate less than those in the other two, while there was no significant difference in eating between the previous-day and control conditions. Interestingly, participants' ratings of their hunger didn't differ in any of the conditions in either experiment. They simply ate less if they remembered that day's meal.

Obviously, memory isn't all there is to hunger (though the data from amnesiacs shows that it's pretty damn important), but this research does suggest one strategy for reducing the amount of food that we eat. Thinking about what you ate for your last meal can cause you to eat markedly less, even if you don't feel any less hungry when you start eating. It's not going to be the solution to all of your dieting woes, but it can certainly help.

¹Hebben, N., Corkin, S., Eichenbaum, H., & Shedlack, K. (1985). Diminished ability to interpret and report internal states after bilateral medial temporal resection: Case H.M. Behavioral Neuroscience, 99(6), 1031-1039.
²Rozin, P., Dow, S., Moscovitch, M., & Rajaram, S. (1998). 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. Psychological Science, 9(5), 392-396.
³Higgs, S. (2002). Memory for eating and its influence on subsequent food intake. Appetite, 39(2), 159-166.