Memory May Play A Big Part In Telling Us When To Stop Eating

When it comes to meal planning, most of us are accustomed to certain portion sizes and we assume we stop eating because we know when we’re full. However, there are a few factors in defining meal size that might surprise you.

In volume, the average adult human stomach holds about the equivalent of one liter of food. But it can also stretch to hold up to about four times that amount, similar in size to a one-gallon water bottle, so no wonder it feels full after a big meal. Unlike many regions in the world, most of us in the west have access to abundant food on a regular basis. Our challenge is not finding it, but regulating the amounts we eat for optimum health. So how do we really know how much to eat and when to stop? Apparently it’s more complicated than you’d think. Over the years, there have been a few studies concerning human hunger and satiety. The results have been informative and sometimes surprising. 

Professor Paul Rozin and others conducted a small but significant study in the 1990s based on a hunch he had about the role of memory in eating. The results were reported in the journal Psychological Science and in an article in the New York Times. He worked with three patients with severe amnesia. The participants had such short memories that they barely recalled anything that had occurred more than a minute in the past. He fed them all a meal and then, after waiting ten minutes, they were happy to accept a second meal. After another ten minutes had elapsed since the second meal, he fed them a third. Each subsequent meal was received as eagerly as the first. After the third meal, one of the study’s subjects said that he planned to “go for a walk and get a good meal”. 

Professor Rozin’s team repeated this experiment on three separate occasions and observed the same results each time. They concluded that the participants’ memories played a large part in their willingness to eat yet another meal. When the part of the brain that controlled memory diminished in ability, it seems that the ability to feel satiety went along with it. So when they didn’t remember the meal itself, they didn’t feel full from it. Rozin wrote that memory was possibly “a substantial contributor to the onset or cessation of eating a meal”. “We’re just not very good at remembering what we’ve eaten previously”, says David Just, a professor of behavioral economics at Cornell, “And even when we are, we’re not very good at compensating for it”. 

Our eating patterns can vary from day to day depending on our circumstances. We evolved to survive in times of feast or famine, so it doesn’t do us much harm if the amounts we eat daily vary considerably. As long as we adjust for overeating as well as fasting, we can keep going pretty well. However, the long-held idea that we have an inbuilt regulatory system to control appetite needs reevaluation. As shown in studies, sometimes we can experience satiety just based on anticipated portion size and our expectations about whether the food will satisfy us or not.

A few other factors can affect portion sizes. For example, the dimensions of the plate you use and even the size of the table you eat at. Both these variables affect your perception of the amount of food served in any given meal. 

Also, the presence and behavior of other people can influence how much we choose to eat. A recent study showed that when served by overweight waiting staff, diners tended to order and eat more food. The size of one’s dining companion can affect the amount of food can affect not only the amount of food eaten but its healthiness too. “The people around us greatly influence how much we eat”, according to Professor Just. “We know, for instance, that when people go through a buffet line, they are very reactive to the person in front of them. If the person in front of you takes a lot of food, not only do you feel you have a license to do the same, you actually feel like it’s expected, like you need to do the same or that you’ll look strange if you do something different.” After all, we are social creatures and we want to fit in.

When it’s convenient to eat, we are more likely to continue, and not feel full until we have stopped, according to Traci Mann, who teaches psychology at the University of Minnesota and is the author of “Secrets From the Eating Lab”. The book examines diets and why they don’t work. “The easier it is to eat, the more you’re going to eat” she says, “If you’ve just gone grocery shopping, you’re going to eat more; if you’re at a buffet, you’re going to eat more; if food is sitting within arm’s reach, you’re going to eat more.” When food and snacks are easy to see and reach, we are therefore likely to consume more of them. Storing them in the refrigerator or cupboard out of sight is a simple but effective way to reduce unplanned and unnecessary eating.

Other than making it inconvenient to eat, how else can we allow ourselves food only when we’re truly hungry? Simply drinking a glass of water before a meal can fill us up a little and can reduce the amount of food we’re likely to eat when we sit down to the meal. We can also develop a more mindful connection with the act of eating and the food itself. As it’s precious nourishment entering our bodies to sustain us, it’s hardly surprising that so many spiritual practices include some kind of blessing before eating. Many people eat their evening meal while watching television, but it is actually much more satisfying to eat undistracted, chew slowly and enjoy a sense of community with friends or family if possible. Being fully present for the meal also establishes it in the memory, a factor that ties in with Professor Rozin’s study results.

When we eat clean, natural, nutrient-dense food, we’re more likely to have our hunger satisfied. When the food tastes better, it’s simply more fulfilling. David Just puts it well: “When things are more delicious, you tend to eat less be cause you’re satisfied more quickly. Whereas when something is acceptable but doesn’t taste all that great, you’ll end up eating more to achieve the same level of satisfaction. There is ample evidence for this.” 

So, a lot of our assumptions about appetite may prove to be inaccurate if something as basic as memory can play a large part in how much food we eat. If Professor Rozin had continued to offer meals to his amnesiac patients, how many times would they have eaten? That would likely have been an unethical approach, so we may never know. But considering many of our household pets are opportunistic feeders requiring strict portion control, we could do worse than take the same approach to our own food intake. Then memory and these other factors would not even be an issue.

Original Study:

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

Paul RozinSara DowMorris Moscovitch

Suparna Rajaram