Unaware eating

When was your last memorable meal: last anniversary, birthday, or other special occasion? What about dinner last night at home? While you may actually be able to remember what you ate last night, the details about quantities and how much time you spent eating are likely to be sketchy at best. To a large extent, this is due to the fact that we seldom pay much attention to eating, except perhaps when in a special restaurant, when awareness is part of both the enjoyment and our motivation to maintain a vivid picture of where all that money went. The term “mindless eating” is often used to convey the way in which we consume foods without monitoring the amounts, and has been linked to overconsumption of snack foods and, of course, obesity.

Going back a century or so, Ivan Pavlov was inducing his canine “research participants” to salivate in response to sounds that they had learnt meant that the evening meal was probably on the way. He termed these responses “psychic secretions” to indicate the role of a mental – that is, psychological – process linking the new signal (the sound) to the original stimulus for salivation (the food), rather than an automatic, in-built reflex. At least in humans, it is generally considered that a such learned connections must be conscious – we are not going to salivate to the sound of a bell unless we know that it signals dinner. However, awareness is not an “all or none” phenomenon and it is often the case that, once learning has taken place, we do not pay attention to those cues that induce a desire to eat or that influence what we want to eat or how much we eat.

Two adjacent papers in a recent issue of the journal Appetite show, in quite different ways, how eating can come under the control of cues outside of our immediate awareness. Feel like you are a free agent in your food choices? That you make these choices according to your appetites, or values, or needs? Gaillet-Torrent and colleagues [1] show that pre-exposure to an ambient pear odour induced their participants to more frequently select a fruit-based dessert for their lunch than those who were not exposed to this odour. These researchers argue that the pear odour ‘primed’ a later food choice that was consistent with the odour quality, namely fruit. Consistent with this, there was no impact of the odour on other, non-fruity lunch courses.

Is this a surprise? After all, the smell of chicken roasting obviously influences our desire to consume that chicken rather than, say, a tuna salad. However, the key here is awareness. The odour exposed group showed no indication on questioning that they were consciously aware of the pear odour that had been present in the room in which they waited for the experiment to commence. And the effect was not merely a slight bias towards the fruit dessert. The control group, not exposed to any odour and hence able to provide a measure of the relative attractiveness of the fruit dessert, choose the alternative dessert – a brownie – by a margin of 3 to 1. So the priming odour not only pushed choice towards one dessert but substantially away from one that might have been chosen otherwise.

A tendency to overeat while paying attention to television is well-known as a prototypical example of mindless eating. But it has not been clear why this occurs. Does an engaging TV program simply distract us from actively monitoring what we eat? Lucy Braude and Dick Stevenson [2] studied this phenomenon, asking whether the increased intake was a function of TV interfering with either (or both) the hedonic changes that occur during eating (a decline in liking known as sensory-specific satiety) or the ability to pay attention to our internal cues signaling reduction of hunger or increasing fullness.

The study asked participants to consume either a single snack food or a variety of different snack foods while either watching TV or not. Replicating the already established findings that both watching TV and food variety produced increased energy intake, this study also showed that liking decreased for the food or foods eaten – the effect of sensory-specific satiety (SSS). However, the most interesting aspect of the results was that while, as expected, eating a single food results in a decrease in liking for that food, this decrease only occurred in the no TV condition. In other words, watching TV eliminated the SSS that we would expect to occur. Eating a variety of snack foods, which produces less SSS in any case, was, in contrast, unaffected by TV watching.

While hunger and fullness ratings did not change due to watching TV, intake (as mentioned above) did. Essentially, this means that greater amounts of snack food were consumed while watching TV to produce the same ratings of fullness and hunger as those who did not watch TV. Both this finding and the effect of TV on SSS are interpreted by these authors as reflecting a disruption of our largely automatic monitoring of both sensory pleasure and cues for hunger. Thus, those bits of the mind that watch what we eat are largely absent: true mindless eating.

Both of these studies shed light on the hidden influences that shape what we eat. Overconsumption is a major concern among many populations and the failure of weight-loss diets to work in the long term is well established. It is recognized that part of the problem is that we are constantly exposed to cues (odours, sights, and even sounds) that signal foods and drinks, especially those high in fat or sugar, making it difficult to resist the associated conditioned impulses to eat [3]. Demonstrating that substantial influence over what and how much we consume can be exerted by cues that evade awareness only emphasizes how difficult the process of exerting control over food intake can be. Conversely, of course, active attention to eating ought to be a means of regaining control. The problem is that lifestyles in many affluent countries work against this. It is no coincidence, I think, that my colleagues in France, where for an affluent country there is relatively low levels of obesity, sit down to eat a substantial meal twice a day (see: http://prescotttastematters.blogspot.nl/2012/12/le-topic-du-jour-gout-qui-importe.html). For them, snacking on the run or while watching TV has been relatively rare.

                                                                                                                       

1.  Gaillet-Torrent, M., et al., Impact of a non-attentively perceived odour on subsequent food choices. Appetite, 2014. 76: p. 17-22.

2.  Braude, L. and R.J. Stevenson, Watching television while eating increases energy intake. Examining the mechanisms in female participants. Appetite, 2014. 76: p. 9-16.

3. Ferriday, D. and J.M. Brunstrom, How does food-cue exposure lead to larger meal sizes? Brit. J. Nutr., 2008. 100: p. 1325-1332.