Food Choice I Lecture - PDF

Food choice I The broader problem and innate factors Based upon Logue Ch.5 Appetite: The psychology of eating and drinking 1 1 What dictates human food choice? • In the next three lectures we will examine the factors that dictate what foods we choose to eat • Before we start, some definitions -...

Food choice I The broader problem and innate factors Based upon Logue Ch.5 Appetite: The psychology of eating and drinking 1 1 What dictates human food choice? • In the next three lectures we will examine the factors that dictate what foods we choose to eat • Before we start, some definitions - liking and preference – Preference is relative (would you prefer to eat a stale bread crust or a deep fried spider?) – Liking is absolute (you would probably like neither) • To get a sense of the specific questions we need to ask about human food choice we will start by looking at the broader problem, which I have illustrated on the next slide 2 2 1. There are around 0.5 M species of plant and 2 M species of animal… 2. Probably the majority (80%) of plant and animal species are edible, and many fungi and algae etc too 4. One class of biopsychosocial factor are the innate systems that guide our food choice. 5. These innate systems help us select what is safe (i.e., they help determine B.) and they influence what our culture calls food (i.e., C.), as well as our individual food choices (i.e., D.). 3. Yet only around 2-400 species of plant and animal are eaten - limited historically by availability, and now by commercial imperatives, but most importantly by biopsychosocial factors. 3 Omnivore’s problem = which subsets are safe to eat? 3 Why study food choice? I • Why is it important to study human food choices? – Dietary choice has a major effect on health • Obesity/overweight increasing at 1% per year – 40% of ALL Australians currently overweight or obese, 60% for adults impact on mental health - quality of diet – Estimated that 1 in 3 Australians will be obese by 2025 and correla4on to depression • Avoidance of dietary related cancer and heart disease – Processed meats [colon cancer], saturated fat [heart disease] – Consequently, we need to know if and how we might alter peoples preferences and how we can generate healthy food choices • Apart from better health, one consequence of this would be to save substantial sums of public money currently spent on diet-related diseases (about 1 billion$/year in Australia) • And understanding food preferences is also vital for making money… 4 4 Why study food choice? II • To create new food and drink products, or to increase sales volume, you need to understand • What people like • How to make them like it • How to make them like it more • The food business is big business in Australia • Processed food manufacture in Australia had a turnover of 74 Billion dollars year over the last decade • Fast food sales alone in 2015 were worth 17 Billion dollars • Food and liquor sales account for nearly half of all retail spending - a whopping 112 Billion dollars • Food exports are worth 30 Billion dollars to Australia each year – around 11% of our exports – and processed food is both the largest growing sector and the most profitable • Remember this, because the food business has the government’s ear 5 5 Innate preferences • Although it is simpler to split our discussion into genetic vs environmental influences, be aware that they generally interact – Bitter sensitivity moderated by parental influence • Our focus here is on food preferences that are primarily influenced by genes • We will examine five cases – Sweet – Milk - Salty - Bitter - Personality factors (but neophobia in L2) • Note, however, that our predisposition to learn from our and other peoples experience with food is the most important genetic disposition capacity to learn about food 6 6 Sweet • In almost every animal studied (excepting certain carnivores, where the sweet receptor gene is dysfunctional), a sweetened food will be taken in preference to a non-sweetened one • Why? In the environment, a sweet food usually signals calories (energy) and sweet foods are typically quite rare (being honey, honey ants, fruits) • Our liking for sweet foods has had many effects • • • • It was a significant impetus for African slavery (sugar cane) It is indirectly responsible for the current dictatorship in Fiji 20%+ of daily energy intake in US adults from added sugar Sugar sweetened soft drinks are a key factor in obesity – The body can not properly measure energy in a liquid, so minimal compensation, and no feeling of fullness 7 7 Is it in our genes? • One obvious place to look for innate preferences is in newborn babies – Maone found that even premature babies preferred sucking a sucrose impregnated nipple to a plain one – Steiner found that day old neonates and even babies with cortical damage (hydrocephalus) showed an ‘ingestive facial expression’ when given sucrose 3. Similar to rats 1. Baby with hydrocephalus 2. Babies after tasting sucrose 8 8 Any role for experience? • Perhaps experience exerts a more subtle effect on our preference for sweetness… – Amniotic exposure – And such exposure is powerful (vanilla breast milk formula; garlic, aniseed) but no evidence to date – Pre-lacteal sucrose (prior to a milk feed to get them to suck) – These babies prefer sucrose to those who have not had it, but the effect wanes rapidly (neophobia?) • However, rat studies suggest no effect on preference for early exposure – Rat pups given 0%, 12%, 48% sucrose (matched for energy) – Later all the pups preferred the 48% solution suggesting that experience had little effect on preference – Context - sweet is good in some foods but not in others (e.g. bacon & maple syrup vs. steak & maple syrup) – Context experiment on kids (tofu presented as sweet, salty or plain – the kids got to like the one they were exposed to and disliked the others on test) 9 9 Other evidence? • We might expect that if experience affected sweetness preference, then such preference should increase with age (exposure) as it does for chilli pepper and alcohol – Yet sweet preference actually decreases with age, with a peak at around 15 • If then there is not much evidence favouring an experiential explanation of this preference, how might the body ‘build it in’? 10 10 Physiology • The tongue has one type of sweetness receptor, all of which pass their signals to the chorda tympani nerve • This nerve has more fibres dedicated to‘sweet’(i.e., more labelled lines) than to any other taste • These fibres pass via the NST to several areas of the brain that seem to drive our liking for this taste – Periaqueductal grey and the nucleus acumbens shell • These are both brain reward areas (rats will bar press for electrical stimulation in these locations) • These areas are rich in endogenous opioids, which is why… – Rats fed sucrose can endure more pain on the hot plate test, a phenomenon that is naloxone sensitive – Sweet tastes in children reduce pain during circumcision and injections – Naloxone reduces sweet liking in adults – And ‘opiate-like’ withdrawal syndrome in mice – Brain stem ingestive areas • Drive reflexive ingestive expressions and behaviour 11 11 Genetic evidence I • First, the continued consumption of sweetened foods in fructose intolerance – Fructose intolerance is caused by an inability to move fructose across the gut wall – It makes the person quite unwell (abdominal pain, diarrhea, bloating, nausea) if they consume it – Even with these consequences many people with this condition continue on occasions to eat sugar rich foods • Second, the failure to find any difference in sucrose consumption/liking between MZ’s & DZ’s – There was such strong selection pressure for liking sweet things most of us are quite similar in this regard (i.e., as an extreme example, imagine the concordance between MZ and DZ twins for no variability number of eyes) 12 12 Genetic evidence II • Third, preference for sucrose can be bred in, at least in rats – Most of us (and rats) have an inverted U shaped liking response to sucrose as a function of its concentration – The concentration of peak liking can be shifted upwards by selectively breeding the rats who like very sweet things • Fourth, sucrose liking is reduced in‘supertasters’ – They have more sweetness receptors so they need less sugar to get the same ‘hit’ as someone with fewer receptors • Fifth, all cultures to which sweet food has been introduced have readily consumed it and continue to do so (Eskimos) • In conclusion – we are ‘hard-wired’ to like sweet things, although the environment can modulate this somewhat (i.e., context) 13 13 Salt • Many animals (and people) will go to great lengths to obtain salt, which is not always readily available in the environment – During Idi Amin’s reign in Uganda the appearance of salt in Kampala markets triggered riots, as salt was hard to come by after he had expelled many Asian shop keepers – Salt was a UK government monopoly in India and formed the basis for Gandhi’s greatest political demonstration with his visit to Dandi to make salt – 80,000 people followed him, Gandhi was imprisoned to massive international media coverage, much to the embarrassment of the UK authorities • Salt is an essential part of our diet and lack of it is fatal – This is reflected in the origins of the word salary which derives from the Roman word for salt ration • So what happens if we become salt deprived? 14 14 Salt deprivation - physiology • Salt deprivation results in two things… – Dehydration (the body expels water to boost blood salt concentration) • This triggers the kidney-renin-angiotensin system, which induces a desire to consume salt – Sensory change – Salt deprivation results in no change in the taste nerve’s sensitivity to lowere sensi*vity to high concentra*ons (want more) salt, but a lower response to high concentrations – The same also occurs for certain brain neurons • The effect of this is too make the animal/person prefer a higher salt concentration than before 15 15 Salt craving in humans I • Babies may not be initially sensitive to salt (so no faces data) – Babies have readily consumed high salt formula after mixing errors, they just can not taste it • However, by four months they readily consume and react to salt – Interestingly, mothers who were dehydrated during pregnancy have children who show a preference for higher salt concentrations than controls • This might be another example of epigenetic changes, in which the expression of particular genes is changed in the foetus based upon the environmental conditions that the foetus may face when born (c.f. Danish starvation study & thrifty phenotype) 16 16 Salt craving in humans II • What evidence do we have in humans that salt craving is under direct physiological control? – Wilkin & Richter, 1940 - Adrenal tumour patient • …At 18 months he was just starting to say a few words and salt was among the first ones. We had found that practically everything he liked was salty, such as crackers, pretzels, potato chips, olives, pickles, fresh fish, salt mackerel, crisp bacon and most foods and vegetables if I added physiological changes leads to intense salt cravings salt… – Salt preferences peak in adolescence suggesting hormonal influence – Salt ingestion (greater preference) in cold climates and blood pressure (mice study on frostbite) – Exercise and salt preference (participants add more salt to soup for up to 12hrs after vigorous sweat-inducing exercise) 17 17 How much do we need? • A preference for salty food is a good thing when it is in short supply • Recommended daily allowance in adults is 6g – roughly equivalent to the salt in one slice of pizza • Most adults consume around 12g/day, which exerts an upward effect on blood pressure, increasing risk of stroke and other diseases • Can experience exert any effect over preference/liking for salt? • Yes. Several longitudinal studies indicate that low salt diets reduce preference for saltier – Parallel examples seem to exist for fat (going from normal to low-fat milk) and sweet • Food labeling – Note that if you wish to calculate salt content from food nutritional labeling multiply the ‘sodium’ value by 3 to give the quantity of salt present. Is this deliberate obfuscation? Some believe it is, because it appears to reduce the quantity of salt in food. 18 18 Salt in food • Although reducing salt intake would have a clear effect on population health via reduced blood pressure and its impact on strokes and kidney disease this is difficult to instigate • The main reason is that most of our excess salt consumption occurs passively in processed food – It is added as a bulking agent (often to processed meats) as this allows a food to contain more water (cost reduction) – It is a useful preservative – It provides the flavour to many processed foods (notably breads) 19 19 Evolution and salt craving • Cystic fibrosis is a common genetic disorder, which affects the intestines and airways • Around 1 in 30 Caucasians carry one copy of the abnormal gene (you need two copies to develop the disease) • Carriers of the cystic fibrosis gene excrete far less salt (via faeces) than non-carriers, which could be life saving if you experience diarrhoea (e.g.,—> from cholera etc) excrete far less salt —> would not get dehrydated • This is called a ‘heterozygote advantage’ and may explain why this deleterious mutation has been retained in the population 20 20 Bitter (and ditto for sour) • Just as neonates find sweet tastes appealing they demonstrate facial expressions indicative of disgust when given bitter tastes • These expressions are nearly identical to those obtained in animals and in children with cortical damage, suggesting an innate origin • Why should this be so? • Primary reasons is that most plant alkaloids (e.g. nicotine, atropine, solanine) are poisons and most taste bitter (poisonous animals bitter and colourful too) • So it is a useful‘safety-net’ to reject a food if it is bitter 21 21 Experiential effects • Exposure does appear to affect preference for bitter foods, even if that preference is initially governed by our genes - for example – The Aymara of Latin America will reject bitter tastes at much lower concentrations than other groups, though not differing in sensitivity • Their diet is heavily dependent on potatoes • Potatoes can contain dangerous levels of solanine and chaconine – Tamarind consuming peoples (e.g., from the Karnataka region of India) will accept levels of bitterness that are not tolerated by most Westerners, again with equal sensitivity – Babies fed protein hydrolysate formulas (which are bitter) come to prefer them to normal formulas 22 22 Milk • Being a mammal is synonymous with the consumption of milk in infancy • Milk is slightly sweet (7% lactose) and so its ready consumption by infants is perhaps no surprise • As no animal consumes milk into adulthood, the puzzle is why Northern Europeans (and their lineage) can and do • The‘can’ question we will address here, the‘do’ question we will examine later (would you drink dogs or human breast milk for that matter?) 23 23 Lactase • The ability to produce the enzyme necessary for digesting milk (lactase) is lost at the age of 2-3yrs in most humans • Is then the ability to tolerate milk in Northern Europeans a consequence of exposure (i.e. continued consumption) or of a genetic ability to produce lactase? – Exposure to milk in adult lactose intolerant individuals does not increase lactase production – However, no one has tested whether early exposure immediately following weaning is important but animal studies suggest this will probably not work either 24 24 Genetic control of lactase I • The ability to produce lactase into adulthood appears to be genetically based • There are two evolutionary arguments: – First, in pastoralist societies a famine meant death unless you could digest milk – Second, Vitamin D assists absorption of calcium, but Vitamin D production is reduced in more northerly latitudes, so less calcium is absorbed • Lactase assists the absorption of calcium from all foods, including milk • On this basis pastoralists from cloudy regions would benefit from being able to produce lactase 25 25 Genetic control of lactase II • The pastoralist account is supported by the presence of lactose tolerance in: – A north-south gradient in Europe (i.e., correlates with average cloud cover) – In all pastoralist societies (e.g., Tuaregs in Africa) • Genetically, lactose tolerance is dominant, so it can spread fairly rapidly into new populations 26 26 Personality • Personality traits are quite strongly heritable (we will deal with neophobia in the next lecture) • Several such traits can influence food preferences – The ‘big five’ • Conscientiousness is associated with higher fruit and veg intake • Ditto for agreeableness and openness to experience • Sensation seeking (which is closely related to openness to experience) is associated with preference for hot and spicy foods, and foods that may be risky to eat (raw meat, shellfish) – Impulsivity • Impulsivity is associated with excess weight gain and obesity • More specifically it is linked to consumption of fast foods, processed foods, and soft drinks 27 27 Genes - Conclusion • There are strong genetic influences on our preference for sweet, salty and bitter foods, in our ability (or not) to drink milk, and in the way our personality shapes our food choices • However, the most important genetic influence is our capacity to learn about what we and others eat • And learning is the main focus of the next lecture 28 28 Food choice II Biology, Experience and Development Based (roughly) on Logue Ch.6 Appetite: The psychology of eating and drinking 29 29 Food choice II • There are three things we are going to address in this lecture – The first is to examine a biological theory of food choice • In essence this theory states that our bodies drive us to eat particular foods so as to meet specific biological needs – The second (and our main focus) will be to examine the contribution of experience to the construction of our food likes and dislikes • As you will see many experiential factors can influence our food choice – The third - which relates to both of the above - will be to consider how babies go from consuming just milk to having a full range of adult food likes and dislikes • People have attempted to answer this developmental question both via the biological needs model and through the experiential and innate factors studied today • We will also see how the innate factors inter-lock with experience-based mechanisms, which is why I have deferred discussion of neophobia (an innate factor) into this lecture (more below) 30 30 A biological needs model of food choice • Many people believe that our food likes and dislikes – and what we eat on a day-to-day basis - may be shaped by our biological need for specific micro and macronutrients, so for example… – If your body is deficient in iron then you might desire iron-rich foods – If you have eaten too much fat, then your body may drive your preference for low fat foods – Perhaps your body is short of a specific B group vitamin, then you might crave foods rich in this • This model then suggests that if we could freely choose from all available foods, we would select a diet that perfectly meets our bodily needs • This is termed “The wisdom of the body” and is a biological theory of food choice – but is it true? 31 31 Wisdom of the body I • The idea that our bodies can naturally select a nutritionally complete diet developed between 1900-1960 • A key human finding was Clara Davis’s study of toddlers in 1935, which was an extension of similar work done in animals – 15 toddlers from 6-11 months reared in hospital – Stayed in hospital until aged 4-5 years – They were offered at every meal a range of nutritious foods (milk, fruits, meats, vegetables etc) – Although children‘binged’on particular foods, in the longer term they appeared to select a fairly balanced diet 32 32 Wisdom of the body II • Two major concerns have been raised about Davis’s work – Modeling • We know (and see later) how social interaction has a very powerful effect on food preferences • Under circumstances where the child has persistently fed on cheese, would there really be no pressure from the nurse to change diet? – Restricted range • The children tended to prefer the sweetest foods. Imagine what the results might have been if coke, biscuits, crisps and sweets had been included • Davis herself concluded “Self selection can have no value if the diet must be selected from inferior foods” • She was well aware of the limitations of her study but secondary sources have obscured this critical caveat 33 33 Wisdom of the body III - animals • Setting aside salt, the strongest claims for the ‘wisdom of the body’ theory in the animal literature come from studies examining thiamine deficiency in rats • It has been suggested that rats can select a diet rich in thiamine (vitamin B), if they have been thiamine deprived • However, this effect may result from the rats developing an aversion to the thiamine deficient diet – That is the rats come to associate the thiamine deficient food with illness – Even this analysis is controversial because some claim there is no evidence for thiamine selection at all 34 34 Wisdom of the body IV - animals • A broader look at the animal data is not very compelling (again setting aside salt) • Early studies often lacked statistical analysis • A meta-analysis of dietary choice studies and specific nutrient studies in animals found no overall effect – That is in many cases animals could not self select a healthy diet or one that remedied a particular nutritional deficiency • When more palatable alternative are available animals eat them (in preference to ‘healthy’ food) and can and do become obese – just like people • If people or animals are ill, they do not seem able to tell the difference between pathogen induced illness and illness resulting from nutritional deficiency – as exemplified by the history of scurvy… 35 35 Wisdom of the body V - scurvy • Scurvy is caused by a lack of vitamin C (see pictures on the opening slide) – The gums swell and bleed, wounds do not heal, the body becomes spongelike and fatigue is soon followed by death • Scurvy was the curse of European Navies, killing more men than enemy action in the 17/18th century and was often thought to be syphilis • It took nearly 200 years to discover that lime juice could guard against its development and this was only established experimentally – That is it took the world’s first clinical trial to identify the link between diet and this nutritional deficiency disease • If the body was so ‘wise’ why were not all involved, drawn to the appropriate dietary solution? • Indeed, this has been the case with the other micronutrient deficiency diseases in human (and animal) medical history 36 36 Wisdom of the body VI - conclusion • We do not show much ‘wisdom’ for micronutrient choice – Salt is the exception and may be so because it is a critical need, and also it can be directly perceived - and even then we eat too much of it! • We do not show much ‘wisdom’ for macronutrients either – However, we are tuned by natural selection to cope with periods of famine and plenty, and this may be why we like and over-consume sweet and fatty foods – There is also a suggestion that we may be tuned to eat a particular ratio of carbohydrates to protein • So the idea that biological need for specific nutrients drives our food choice (and indeed food cravings) is not well supported 37 37 Experiential factors • There are a large number of mechanisms that affect food likes and dislikes – validated in and out of the laboratory – that rely upon our experience with a food • There are two overarching themes here – Mechanisms that assist us in selecting what is safe – Mechanisms that assist us in finding and choosing foods that are energy-dense • We will also, in passing, look at some of the mechanisms that cause shorter-term changes in what we like (i.e., within a meal) 38 38 Back to genes - neophobia • Any experiential mechanism has to conquer food neophobia! • Food neophobia is a reluctance to try unfamiliar foods • Food neophobia has several characteristics – – – – It is seen in rats (bait shyness) as well as people It varies from person to person just like other personality characteristics It is a stable trait Babies around weaning seem to mouth anything, but as they are initially exposed to foods, they start to demonstrate neophobia – Males are generally more neophobic than females – Neophobia decreases with age • High neophobes think they will dislike a new food more than low neophobes. Although contentious, hedonic ratings for the target novel food may not differ much when both groups actually taste it 39 39 Conquering neophobia – Mere exposure I • We prefer foods we are familiar with, so perhaps just mere exposure to an unfamiliar food might increase preference and liking - and it does… – Fruit juices in the lab (guava, mango, soursup - liking problem) – Donut eating in an Alaskan fish cannery (consumption measure overcomes liking problem) – And children too (kiwi, papaya, lychee, palm - only exposure to flavour works) – Amniotic flavour exposure (vanilla, aniseed) – Lacteal exposure (garlic, vanilla - ketchup study, alcohol) • How does it work? – Leaning that it is safe (explicitly or implicitly) – Perceptual fluency (the ‘warm glow’ of the familiar) 40 40 Mere exposure II • It may be quite difficult to get people (especially the most neophobic) to try all of the foods available within a particular culture • Human society has developed a neat trick to get round this • Particular cultures tend to use particular combinations of flavours, for example… – Tomato and oregano in Italian cuisine – Soy sauce, rice wine and ginger in Chinese cuisine – Fish sauce, limes and chilli in Thai cuisine • There are many such culture specific ‘flavour principles’ (and you can see lots of them in Elizabeth Rozin’s Flavour principle cook book) • Thus unfamiliar foods can be introduced within the context of an already familiar flavour 41 41 Mere exposure III • When thinking about exposure effects we also need to think about the time frame – Short-term (within a meal) • In this case liking is reduced - sensory specific satiety – This is an important mechanism for encouraging variety within a meal and limiting consumption of one specific food – For example the nurses sandwich study (4 flavours vs 1) – Buffets, choice, eating more and obesity – Mechanisms may differ [habituation] – and neural basis understood – Long-term (between meals) • Preference for the exposed food grows to a peak • Demonstrated and discussed on the previous page – Very long-term (weeks) • Monotony reduces liking • This can also be important in advertising as some research suggests that over-exposure can breed dislike 42 42 Learned likes I • Associative learning (i.e., linking two events) represents a well studied means of changing liking for a food and it may occur in several different ways – (1) Associating a food flavour with calories • Hi-cal food paired with flavour 1 and Lo-cal food paired with flavour 2 (only flavour differs) and test by liking ratings or consumption • Many laboratory studies support this process in humans and animals • Its main impact may be on liking for the sight of the target food or its smell as this can then help the person (or animal) choose/find that energy rich food in the environment • A significant problem NOW is ecological validity – Multiple foods in a meal, so multiple potential causes of energy, so how does the body know what to associate with what? – Perhaps this was not a problem in the ancestral past, where single foods were eaten to repletion (and how do we know – studies of hunter gatherers) 43 43 Learned likes II (2) Associating a food flavour with sweetness • • • • Tea flavour experiment (and liking for tea and coffee?) Relationship to odour-taste synesthesia Can generate dislike (too sweet; and bitter and sour) Again assists in identifying foods via sight and smell that probably taste good – and good (i.e., sweet) signals energy! • Similar caveats about ecological validity as for (1) (3) Medicine effect • Associate flavour of a medicine with its power to make you feel better – some animal evidence, but no convincing evidence in humans (4) Drug-flavour learning • Humans and animals can come to associate flavours with particular drug-related effects, with this demonstrated most convincingly in humans with caffeine (we like flavours associated with caffeine delivery, especially if we have missed our morning coffee) 44 44 Learned dislikes • What about learned dislikes? – Many of us report having conditioned taste aversions (or perhaps more properly it should be conditioned flavour aversions) – These typically occur to unfamiliar foods or to foods of animal origin – Long delay between ‘cue’ and ‘consequence’ • As sickness may be delayed (up to 24 hours) – Specific to gastrointestinal symptoms which is the best example of biological preparedness in the learning literature • Bright noisy water experiment – Animals associate flavour with sickness and noise/light with footshock, but not flavour with footshock or noise/light with nausea – Can be persistent (but not unchangeable) • But only because of reluctance to reconsume – Occur irrespective of conscious awareness • Cancer chemotherapy, Gastric flu, Chronic malaise in children and Incidental aversions in infants 45 45 Social learning I • Social learning occurs when we copy other peoples actions or we learn from watching them. This can occur with or without intent • Social learning is pervasive and powerful – It can be readily observed in animals • • • • Rats develop an aversion to food smells associated with dead rats Food smelled on a healthy rat’s coat/breath comes to be preferred Rat pups preferentially feed where there are rat faeces Rat pups preferentially feed where adult rats feed – First observed in humans by Escalona (1940’s) • Babies tended to shift preference for juices dependent upon the preference of the carer (think back to the Clara Davis study!) • Recent studies have confirmed this observation 46 46 Social learning II • Social learning is likely to be an important means by which children develop food preferences – Children come to prefer relatively bland foods (cashews vs pineapple) that are provided by a friendly adult – A child’s peers can also influence food preferences • • • • A young child (the target) is seated at a table with 3 of his/her peers Two types of vegetable are put out to eat The target is known to prefer one type, his/her peers the other The target child soon shifts their preference for the vegetable being chosen by his/her peers – Recall how liking for chilli pepper may develop • Given how social eating is, especially with children, it should not be surprising to learn then how pervasive an influence other people are on what we choose to eat 47 47 Social-cognitive effects • Birch found that if children had to eat a certain (bland) food to obtain access to toys they really wanted to play with they came to like the target food less – This has been termed the‘overjustification effect’ – Children’s cognitions may go something like this “They made me eat it, it must be horrid and so - thus - I don’t like it!” – Think of the implications of this for raising a child on a decent diet – However, the picture may not be so bleak as information can mitigate this effect if it is explained why eating (say vegetables) is necessary • A further effect concerns cognitive dissonance – The Grasshopper experiment - the low renumeration/grumpy experimenter condition produced the largest change in liking for eating a cooked locust (i.e., the participant had to make their attitude consistent with their behaviour to minimise dissonance) 48 48 Advertising I • Of all the forms of social learning TV advertising is by far the most potent, especially in children • In the US, 4.2 Billion US$ are spent per annum on just fast food advertising • Of the 25 biggest advertisers, MacDonalds are 4th and Subway 19th • MacDonalds spends around 960 Million US$ per annum on adverts in the US alone • Kids spend around 3 years of their childhood watching TV and most of the adverts they see are not for healthy foods – 30% of ads in the US aimed at kids are for chocolate/candy, 30% for breakfast cereals and 10% for fast food 49 49 Advertising II • Child orientated ads are most potent when the food or drink is linked with a kids TV character • The research evidence shows overwhelmingly a causal link between watching food TV ads in kids and purchase and consumption of those foods – The foods that children pester their parents to buy are those that they have seen advertised on TV – Viewing such ads produces a preference shift for that food – Exposing children to particular adverts leads to them pestering their parents for that food on a later trip to the supermarket (via hidden tape recorder) and greater likelihood of purchase by the parent • Food ads work and that is why food companies use them! 50 50 Getting from milk to adult-like food preferences • The mechanisms that work to build up an adults repertoire of food likes and dislikes can be seen as the cumulative effect (since childhood) of all of the processes we have just finished reviewing – The primary caregiver initiates exposure to a progressively broader range of foods (mere exposure and social learning) – As the child gets older, they are exposed to more social learning via TV adverts, educational messages and peers – During all of this time they are learning about the energy value of foods and perhaps developing some aversions on the way (initial encounters with alcohol, sickness etc) – All of these influences, combined with a person’s suite of genetic predispositions, shape their adult food likes and dislikes 51 51 Conclusion • As you can now see both innate and experiential factors influence food choice at several levels – What is safe, what can be eaten within a culture, personal preferences • But the most important determinant of what you eat is your culture (see the diagram at the start again) as this defines what is and is not food – this is the focus of the next lecture 52 52