When you sit down to a meal, how do you decide how much to eat? Perhaps it seems a ridiculous question. Most of us would answer that it depends simply on how hungry we are. That is, we eat less when we are relatively full and more when our stomachs are empty. But there is increasing evidence that physiological hunger is only one of many influences on how much we consume. Some recent research suggests, for example, that meal size depends not just on how full your stomach is, but also on your recall of what you have recently eaten.
There are some very dramatic examples of just how important memory can be in determining how much we eat. These come from studies of individuals whose ability to remember recent events has been abolished by brain damage. In one such study, two brain damaged men ate three consecutive lunches, each separated by as little as 30 minutes, because they had no recall of previously having eaten . But what of the rest of us? Surely we can all recall – more or less – what we had in our last meal, and it is obvious that we recall more recent meals better than those from days earlier. So what actual impact does this have in how much we eat now?
Sometimes, eating is very memorable. For most of us, restaurant experiences – particularly at the high-end of dining – are not an everyday experience, and we want to savour and recall a chef’s ability or creativity. As a result, we pay attention to what we experience because this is crucial to the formation of memories. In contrast, everyday meals are very often anything but memorable. This is not because of their quality, but rather due to the lack of attention that we pay to the food while eating in our usual environment. We eat while watching TV, or reading, or texting. But we now know that attending elsewhere, instead of on the food we are eating, has a number of important consequences.
The phenomenon of mindless eating is familiar to most of us. When distracted by our favourite TV program, we will munch through whatever is at hand – popcorn and confectionary, for example – without any real awareness of how much or how fast we are eating. Such distraction can lead to overconsumption, relative to those times when we are more conscious of eating. In particular, according to one recent study , this can be a problem for regular dieters, sometimes referred to as restrained eaters. Here, groups of restrained and unrestrained eaters were allowed to eat sweets (candies) while watching a TV program containing either food-related or food-unrelated material. The content of the program was relevant only for the restrained eaters who ate more calories while watching the food-related TV program. This, incidentally, is a clear example of the fact that restrained eaters are vulnerable to environmental cues that remind them of food.
But such distraction continues to have an effect even after we have eaten. If we do not recall, through distraction, what we have eaten, then at a subsequent meal we will eat more. Female university students were provided with a variety of sweet and savoury snack foods and drinks, with half watching a TV program at the same time . Those students who had watched TV while snacking ate more of a lunch that was later provided than did their less preoccupied colleagues. Nor did it depend, in this case, on the nature of the TV program since a later study explicitly varied the content between humorous, sad or boring (lawn bowls!). Because the researchers had also asked their student participants to estimate how much of the snack foods they had consumed, they were able to explain these results by showing that those watching TV were less accurate in remembering how much of the snack foods they had eaten – indicating that their attention was on the TV program, rather than the food they were consuming.
In a more direct attempt to determine if paying attention to what you eat enhances memory and influences later consumption, another group of researchers asked their students to focus on the sensory properties – the tastes, textures, and odours - of a simple lunch of sandwiches and crisps as they ate, as compared to other groups eating the same meal who either read a newspaper article about food or did nothing . In this case, a selection of sweet biscuits was available to consume in another session two hours later. Those who had earlier paid attention to their lunch ate fewer biscuits than the other students. Moreover, as in the previous study, this group also indicated that their memory of what they had eaten at lunch was much more vivid.
So clearly memory for what we have eaten is crucial in modulating what we will eat. Why? One obvious explanation is that if we recall how much we have eaten, we consciously limit what we subsequently eat to maintain some sort of overall daily calorie intake. While this is plausible, some sort of calorie calculation does not tell the whole story. Examining the response of the student groups in this last study to the different biscuits though suggests another possibility. The two most highly liked biscuits (both chocolate covered) were eaten far more than the plainer, less liked biscuit …. but only by the groups not asked specifically to focus on the food’s sensory properties. If those who were somewhat inattentive to their earlier lunch were highly responsive to the different degrees of palatability of the biscuits, why wasn’t the food focus group?
An alternative hypothesis is that the influence that memory exerts on subsequent intake is really concerned with the memory of the pleasure of eating, rather than the calories consumed. This is consistent with the fact that, much of the time, we are driven to eat by hedonic (that is, pleasure-based) hunger rather than any real need to replace nutrients.
The influence of “memory for pleasure” might explain some interesting cross-cultural differences in eating. Much has been made of the “French Paradox”, also known as the “how come the French don’t get fat even though their food is delicious and rich” puzzle. The French, it turns out, are far more focused on food pleasure than say diners in the USA  whose concerns are less about pleasure and more about the food’s health consequences. It is this focus on pleasure that underlies the satisfaction shown by French diners with smaller portions and the lack of a need to search for food pleasures – snacks - between meals.
So, from a weight control point of view, the message is simple. Distracting yourself from food pleasures – either via TV or via eating unpalatable food – is likely to leave you searching for the pleasure you have missed or can’t recall.
1. Rozin, P., et al., (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 mulitple meal eating in amnesic patients. Psychological Science, 9, 392-396.
2. Shimizu, M. and B. Wansink (2011) Watching food-related television increases caloric intake in restrained eaters. Appetite, 57, 661-664.
3. Mittal, D., et al., (2010) Snacking While Watching TV Impairs Food Recall and Promotes Food Intake on a Later TV Free Test Meal. Applied Cognitive Psychology, 25, 871–877.
4. Higgs, S. and J.E. Donohoe (2011) Focusing on food during lunch enhances lunch memory and decreases later snack intake. Appetite, 57, 202-206.
5. Rozin, P. (1999) Food is fundamental, fun, frigtening, and far-reaching. Social Research, 66, 9-30.