‘The (food) industry is geared to over-stimulating the senses of the consumer so that they can eat more. It is activating parts of the brain that are susceptible to being conditioned to find the product desirable and wanting more of it.’ Gordon Shepherd, Professor of Neuroscience and Neurobiology,
Yale School of Medicine1
WHILST STROLLING ALONG the street, your eye is suddenly caught by the sight of a Starbucks on the other side of the road. Even though you had not, until that moment, felt hungry, you are suddenly seized by the desire for a coffee and chocolate cake. Images of a steaming latte and a slice of mouthwatering gateau flash into your mind. You can almost smell the aroma of freshly brewed coffee and taste the rich, dark cake. A few seconds later, you are opening the door of the shop and stepping inside.
It’s not that you have a physical need for food, but rather that the familiar Starbucks mermaid logo has created a psychological want for it. It cued a memory of just how much you enjoyed coffee and cake the last time you had them. The same might be true of any number of other logos, the ‘golden arches’ of McDonald’s evoking the memory of a delicious burger or the blue and red square of Domino’s Pizza reminding you of the last time you indulged in a feast of melted cheese.
‘Those kinds of cues’, comments Kent Berridge, Professor of Psychology and Neuroscience at the University of Michigan, ‘have the power to evoke the desire to take that thing again.’2
Food cues are all around us. At home, we watch TV programmes and commercials discussing, describing and promoting a vast range of foods and beverages. We read newspapers and magazines filled with recipes and articles about growing, selling and consuming food. Away from home, we are bombarded with the sights, smells and tastes of foods. Billboards and advertising hoardings carry images of food and drink. Pavements are lined with cafés, bars, bistros, fast-food eateries, and fine dining restaurants. There are shops and vendors selling virtually every kind of snack from chocolates and sweets through to soft drinks, crisps, cakes, buns, pasties and hot dogs. For anyone living in a town or city, as soon as the desire to eat arises, it can be easily and instantly satisfied.
Central to this problem is what we might term the ‘see food – eat food’ dieting paradox. Those who most want and need to lose weight are the ones most sensitive to food cues. Their greater vulnerability, of which they are not usually consciously aware, arises for one main reason: they have learned to overeat.
During the early 1980s, Harvey Weingarten of McMaster University in Ontario, Canada, trained rats to eat on command. He did this by pairing the introduction of food into their feeding trays with either a light or a musical tone. The rodents quickly cottoned on to the fact that these cues indicated that lunch had been served. The rats had been ‘conditioned’ to associate a cue with eating. The interesting thing was that when Weingarten then allowed his rats to eat their fill at any time they wanted, the conditioning remained; even if they were completely satiated, if a light flashed or a tone sounded, the rats scuttled obediently to their feeding trays and gobbled up everything on offer.
‘The results demonstrate that cues that have become signals for food can subsequently initiate a meal,’ Harvey Weingarten comments. ‘Once such an association has been learned, stimuli retain their ability to influence feeding for protracted periods and even under a state, satiation, that might have been expected to minimize the impact of such events.’3
Humans, too, can quickly and easily be conditioned to consume anything from food and drink to tobacco and drugs. All that it takes is for an association, at both a conscious and unconscious level, to be established between the stimulation of reward centres in the brain (as described in Chapter 7) and specific cues, or triggers, in the environment. These may be a place, a situation, an activity or a symbol. Some smokers, for example, light up almost without thinking about it when getting behind the wheel of their car, drinking coffee, opening a newspaper or in response to a tobacco advertisement. It’s the same with those primed to respond to food cues. The sight of a logo on a shop front, or an advert flashing up on the television screen can create an impulse to snack on the associated food that is acted upon almost automatically.
If this kind of eating isn’t really scrutinised by the conscious mind, the concern is that we are even less likely to be able to moderate it. We decided to investigate this. In a London cinema, we watched in fascination as an audience, deeply immersed in a Spiderman movie, ate popcorn like zombies. With large buckets resting on their laps, they munched their way through the snack with a methodical mindlessness. Without their eyes ever leaving the screen, their hands descended into the bucket and fistfuls of puffy white kernels were delivered to their mouths. Teeth and lips closed, jaws began chewing. Before that portion had even been swallowed, the hands began to reach down once more and the cycle was repeated.
So what would happen to popcorn consumption if that ‘mindless’ pattern was broken?
To find out we fitted each member of the audience with an oven glove worn on their dominant hand – the one they would usually use to pick up the popcorn. The results were pretty clear; when obliged to eat with their other hand, using an unfamiliar movement, the amount of popcorn people consumed fell by over a third.4
By slowing consumption and actually thinking about the food you are eating you can significantly reduce the number of calories you consume. Mindful – as opposed to mindless – consumption can prove an effective counter to the power of food cues.
Exposure to stimulus will often evoke subconscious thoughts of a second stimulus. The term ‘priming’ describes the phenomenon of how, for example, the word ‘doughnut’ is recognised faster if the word ‘coffee’ precedes it. Similarly, ‘contextual cueing’, a phrase coined by Marvin Chun and Yuhong Jiang of Yale University in 1998, refers to the way the brain seeks out previously identified patterns in its surroundings to identify new or unfamiliar stimuli. As with priming, the effect occurs in the ‘implicit’ or non-conscious memory. As a result, people remain unaware of the fact they are being influenced by, for example, repeated exposure to fast-food logos or familiar pack designs.
At the University of Florida in 2010, Carol Cornell and her colleagues conducted a study in which they explored the ability of two highly palatable foods, pizza and ice cream, to serve as food ‘primes’ likely to initiate eating and appetite.5 They began by offering participants, young men aged from sixteen to twenty-eight, a free lunch and encouraging them to eat until they felt comfortably full.
After consuming around 1,000 calories each, the participants pronounced themselves satiated. They were then separated into two experimental groups and a control group. Those in one experimental group were asked to taste a mozzarella pizza and those in the second a bowl of vanilla and chocolate ice cream. Those in the control group were not given any food to taste. Members of both the experimental groups were instructed to take just one mouthful of the food in order to assess its appearance, flavour and aroma. Once this tasting had been completed, all participants were subsequently invited to eat as much as they wanted of the remaining pizza and ice cream.
The results were intriguing. Those who had tasted the pizza ate more pizza than ice cream, while those tasting the ice cream consumed more ice cream than pizza. On average they consumed an additional 300 kcal each, despite having reported only fifteen minutes earlier that they ‘couldn’t eat another thing’. This strongly suggests that everything further they ate was in response to a ‘want’ rather than a ‘need’. Their preferences were the result of priming (by taking a single mouthful) and cueing (via the obvious availability of the foods).
‘If you have a small taste of something, that can trigger overwhelming desire for that food. Our central problem is that appetite is a function of the circuits in the brain associated with reward; that circuit doesn’t have a particularly strong “stop” signal,’ explains Kent Berridge. ‘So, in our world that circuit can be turned on and left on indefinitely. For some, that leads to issues with controlling our appetites.’6
In the previous study the participants, although left in the dark about the true purpose of the experiment, were otherwise aware of what was going on. However, priming need not always be so obvious. It can, in fact, occur without our ever being aware of the fact.
During the summer of 1957, Picnic, a movie starring William Holden and Kim Novak, was doing roaring business for a cinema in Fort Lee, New Jersey. Billed as a love story between two people ‘electrically attracted to each other’ the film attracted more than 50,000 during its six-week run and won six Academy Awards. A couple of weeks later, a 42-year-old market researcher named James McDonald Vicary announced to journalists that those movie goers had been his unwitting ‘lab rats’ in a mind control experiment which secretly manipulated their desire to eat and drink. Vicary explained how he had installed a device of his own invention in the cinema which projected two advertising messages, one reading ‘THIRSTY? DRINK COCA-COLA’ and the other ‘HUNGRY? EAT POPCORN’ onto the screen as the film was showing.
Although these appeared continually throughout the movie, no one in the audience consciously saw them since they were flashed up for just three-thousandths of a second. Vicary reported that Coca-Cola sales had risen by 18% and popcorn by 58%. His claims created a storm of public outrage and universal condemnation by the media.7 A few years later Vicary confessed it had all been a hoax, a PR stunt to drum up business for his near bankrupt ‘subliminal projection’ company.
For decades after this admission, advertisers vehemently insisted that they never had and never would employ such unethical tactics, while the majority of psychologists dismissed the possibility that subliminal messages could have any effect on behaviour.8 But recent research has shown this confidence to be misplaced; in fact, subliminal cues can exert a significant influence over consumer choice and behaviour.
In one such investigation to determine whether unconscious priming could manifest itself in behaviour, scientists examined participants’ reaction to emotional facial expressions and how much they drank after seeing happy versus angry faces.9
After asking whether or not they were thirsty, researchers instructed the participants to pour and then drink an unfamiliar beverage. They next completed a task that involved identifying whether a face on the computer screen was male or female. The expressions on these faces were either happy or angry.
Immediately after viewing the faces, participants were asked to rate their mood, and were then given the unknown beverage to drink, which was actually pleasantly flavoured with citrus. Both their self-reported mood, and how much of the beverage they consumed was recorded. While there was no detectable difference between participants’ self-reported feelings, those who saw a greater number of happy faces consumed significantly more of the drink.
So it seems you can subconsciously prime people to drink or eat. If that is the case, is it also possible to influence exactly what they choose to eat or drink?
In 2006, Johan C. Karremans and his colleagues in the Department of Social Psychology at Radboud University, Nijmegen, set out to see whether it was possible to persuade thirsty volunteers to favour one beverage, Lipton’s iced tea, over another, mineral water, by using subliminal priming.10
Participants watched a computer screen on which a string of capital letters, such as BBBBBBBBB appeared. Every so often, a lower case letter would occur, for example, BBBBBBbBB. The job of the participants was to detect such differences. After completing this task they were given a salty local sweet, known as a ‘dropje’, to suck, and asked to try and identify a letter embossed on one side with their tongue. In fact this was just a cover story. The true purpose of the salty sweet was to increase their thirst. Next they were offered a choice of two thirst-quenching drinks, either a can of Lipton Ice Tea or a bottle of Spa Rood, a local brand of mineral water.
What those who had asked for the tea did not know was that they had been subliminally primed. While watching the strings of letters flow past them on the computer screen, either the words Lipton Ice or else nonsense control words containing the same number of letters, (e.g. Npeic Tol) had been flashed up for 23 milliseconds. Amazingly, 69% of those who had been subliminally exposed to the brand name chose Lipton Ice Tea, while only 25% of those presented with the control word did so.
‘Our findings suggest that consumer choices may be influenced by subliminal primes,’ comments Johan C. Karremans. ‘Subliminal flashes of “Lipton Ice” on a television screen . . . may alter one’s choice to order Lipton Ice.’
It’s impossible to say whether subliminal advertising is currently being used to prime unknowing consumers to choose a particular brand of food or drink. While we have heard rumours that the technique has occasionally been tried, there is no firm evidence to support such claims. Nor is there any real need for this. Psychologists have demonstrated that behaviours can be just as effectively influenced by cues which, while visible to all, are rarely noticed by anyone.
While subliminal cues are presented too briefly for the conscious mind to be aware of them, supraliminal cues are easily seen, provided anyone attends to them. Supraliminal cues are simply items that you can register consciously, from the irritating jingle on the radio to the packaging colour of your favourite chocolate bar. If the item registers within consciousness, it is referred to as a ‘supraliminal cue’. However, all the research evidence indicates that on most occasions people fail to register supraliminal cues, simply because their attention is elsewhere.
One of the first people to comment on this was the Hungarian neurologist and psychiatrist Resö Bálint. In 1907, he noted that: ‘It is a well-known phenomenon that we do not notice anything happening in our surroundings while being absorbed in the inspection of something; focusing our attention on a certain object may happen to such an extent that we cannot perceive other objects placed in the peripheral parts of our visual field, although the light rays they emit arrive completely at the visual sphere of the cerebral cortex.’11 In short, it’s possible to look at something without consciously seeing it.
The ability of supraliminal cues to influence behaviour has been demonstrated by Esther Papies and Petra Hamstra from the University of Utrecht.12 In their experiment they attached a modest-sized poster, displaying a recipe described as ‘good for a slim figure’, to the glass door of a butcher’s shop. On the counter inside the shop they placed a tray of meaty snacks with a sign inviting people to taste as many as they wanted. One of the researchers stood nearby and surreptitiously counted how many snacks were eaten. The customers were then asked to complete a short questionnaire about their eating habits and say whether or not they were on a diet. After the poster had been up for a couple of days it was removed, but the snacks remained, and customers were still asked to complete the questionnaire.
Papies and Hamstra found that customers who were on a diet had seemingly responded to the ‘slim figure’ recipe – on the days it was up, dieting customers consumed fewer snacks than those not dieting. However, on days when the poster did not appear on the door, they ate significantly more than the non-dieters. The researchers reported that they believed their little poster, although seldom read or even glanced at, had: ‘Overruled . . . the tendency to overeat on the presented snacks.’ As David Kessler, former commissioner of the US Food and Drug Administration comments: ‘Cues can gain power even if we’re not consciously aware of them.’13 Unfortunately, cues that help people lose weight are far less common in the modern world than those encouraging them to gain it.
We’ve mentioned just a few of the many studies demonstrating the power of subtle cues, of which we may not be consciously aware, to influence what and how much we eat. Even if this only involves us deciding to have a second helping of dessert, a bar of chocolate mid-morning, a doughnut with afternoon tea, or a snack when commuting, the calories quickly mount up. An extra 100 each day, the amount in a chocolate bar, will add 16 pounds of fat over a year.
Using functional Magnetic Resonance Imaging (as described in Chapter 7), scientists found that when shown images of high energy-dense foods, the brains of lean and obese individuals responded rather differently. The latter showed greater activation in regions associated with taste information processing (anterior insula and lateral orbitofrontal cortex), motivation (orbitofrontal cortex), emotion (amygdala) and memory (hippocampus).14
Food cues trigger activity within what is called the brain’s ‘appetitive network’, comprising four major areas (described in Chapter 7): the amygdala, hippocampus, striatum, and orbitofrontal cortex. If the food cue is a visual one, a logo, billboard or TV commercial, for example, our eyes will send this information to the visual cortex at the back of the brain. From there, signals are sent to the hippocampus and the amygdala, regions responsible for memory storage and emotions. The hippocampus can simultaneously evoke a powerful memory and direct the individual towards a food reward, while the amygdala can endow that reward with powerful and extremely pleasurable emotion. Ingestion of hyper-palatable food will also excite activity within the striatum, the location of the nucleus accumbens, the brain’s ‘hedonic hotspot’. Once food high in sugar and fat is ingested, dopamine fires within two parts of the brain, in essence from the ventral tegmental area to the nucleus accumbens. It is this reaction that accounts for the hugely pleasant feeling we get when we eat hyper-palatable food. Finally, the orbitofrontal cortex (OFC) provides feedback, direction, and guidance for conscious action, leading us towards consumption or restraint from highly pleasant food. By the way, this entire process is happening almost below conscious awareness, simultaneous with the conscious pleasure of the ‘Mmmm’ when we bite into a delicious burger, or the, ‘Those biscuits look nice,’ when we pass them in the supermarket.
So, food cues alter activity in almost every part of the brain associated with motivated action. ‘There is significant overlap with the regions in the brain that are associated with motivation and appetitive drive,’ comments Kent Berridge. ‘Once you initiate appetitive networks, in certain individuals you may also trigger motivational action. Since nice tasting food is almost everywhere, this can be a really difficult issue for people who struggle to turn the switch off.’15
In essence, seriously overweight individuals are far more sensitive to food cues than the majority. Not necessarily because they were born that way, but rather through a course of life-long learning. As with Harvey Weingarten’s rats, mentioned earlier in the chapter, they have become conditioned to respond to even subtle food cues with an almost overwhelming desire to consume HED foods.
Kent Berridge and Terry Robinson, from the Department of Psychology at the University of Michigan, have investigated the differences between wanting food and feeling hungry, what we termed homeostatic and hedonic motivation in Chapter 7. 16
As we have explained, when we eat high energy-dense foods, dopamine and opioids flood the brain’s reward centres, establishing or reinforcing powerful memories of the pleasurable experience. These can be stored as ‘explicit’ memories, of which we are consciously aware, but also as ‘implicit’, or subconscious, memories that can only be deduced from our behaviour. Whenever possible, advertisers and marketers seek to embed priming memories as deeply into the subconscious as they can. When they are able to do this, responses to their food cues become more reliable, since it is our implicit motivations – the ones of which we are not consciously aware – which are most intimately linked with our behaviour as consumers, as opposed to our explicit conscious ideas of what we should like.
‘Liking’ refers to explicit preference, the way we might say we like the colour blue. Liking tends to be a relatively innocent expression of preference. It is ‘wanting’ that causes so many issues with appetitive behaviour. While liking sets the stage for our actions and decisions, wanting determines our degree of motivation to buy something, or to eat it. Wanting is generated by the emotional centres of the brain, which include the nucleus accumbens and amygdala. For example, stimulation of the nucleus accumbens produces a voracious appetite in laboratory animals, especially for high sweet, high fat, foods.17
So it is clear that psychobiological factors affect our appetite. It’s not simply that we think some foods ‘taste nice’, but rather that some foods, such as those high in sugar or fat, elicit a psychological, emotional feeling of pleasure. Both ‘liking’ and ‘wanting’ have an explicit, conscious aspect and implicit unconscious one; it is the implicit side which is the most problematic, tied up as it is with craving. As all dieters know, consciously deciding to go on a diet is the easy part. Resisting cravings is where things start to fall apart.
According to Berridge and Robinson: ‘Wanting is a motivational, rather than an affective component of reward’, which is to say that we may not be aware of how much we ‘want’ something until we feel that burn of craving it. It ‘transforms mere sensory information about rewards and their cues (sight, sounds, and smells) into attractive, desired, riveting incentives.’18
It is known, for example, that repeat exposure to drugs can powerfully affect ‘wanting’ while ‘liking’ remains unchanged.19 Within a very short space of time the ‘wanting’ can become so intense that it overwhelms any attempts at self-control. In the case of both drugs and food, this results in increasingly irrational and health-destructive behaviour.20
As scientists strive to make sense of this complex set of interactions, an important focus of obesity research is likely to be the hormones that act in concert with dopamine. This may, in time, lead to more effective ways of targeting overeating behaviour – perhaps even with the development of a weight-reducing pill. At the time of writing, new drugs that feature ‘opioid agonists’, such as naltrexone, have just been approved for use by the Food and Drug Administration. Naltrexone blocks opiate receptors, making highly palatable food less rewarding. While such pharmacological efforts have yet to have a significant impact in the battle against obesity, researchers remain hopeful of coming up with an effective drug.21
In summary, food cues contribute to triggering the motivational chain of events in the brain related to acquisition and consumption of food. Thus, they play a central role in explaining why it is that some people are more vulnerable than others to our ‘obesogenic’ environment. What precisely these food cues are and how they trigger the desire to overeat will be explained in the next chapter.