Food Choice

Question 1

What is the difference between preference and liking?

Answer 1

– 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)

Question 2

What is the omnivores paradox?

Answer 2

The omnivores paradox: there’s an enormous range of foods out there but only a subset is fit to eat. Our problem is determining what is fit to eat
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
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.
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 and they influence what our culture calls food, as well as our individual food choices.

Question 3

Why study food choice? (5)

Answer 3

– Dietary choice has a major effect on health
– 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
• 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

Question 4

What affects our innate preferences?

Answer 4

Genetic and environmental influences generally interact
Our predisposition to learn from our and other peoples experience with food is the most important genetic disposition

Question 5

What is our preference for sweet food?

Answer 5

• 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

Question 6

Is our preference for sweet in our genes?

Answer 6

– Premature babies preferred sucking a sucrose impregnated nipple to a plain one
– Day old neonates and even babies with cortical damage (hydrocephalus) showed an ‘ingestive facial expression’ when given sucrose

Question 7

Does experience have a role in our preference for sweet? (5)

Answer 7

• Perhaps experience exerts a more subtle effect on our preference for sweetness
– Amniotic exposure: 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

• If experience affected sweetness preference, then such preference should increase with age (exposure)
– Yet sweet preference actually decreases with age, with a peak at around 15

Question 8

What is the physiology behind our preference for sweet?

Answer 8

• The tongue has one type of sweetness receptor, all of which pass their signals to the chorda tympani nerve
• This nerve has more fibers dedicated to ‘sweet’(i.e., more labelled lines) than to any other taste
• These fibers 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
• 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

Question 9

What is the genetic evidence for our preference for sweet? (5)

Answer 9

• The continued consumption of sweetened foods in fructose intolerance
– Fructose intolerance is caused by an inability to move fructose across the gut wall
– Even with the consequences many people with this condition continue on occasions to eat sugar rich foods
• 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
• 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
• 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
• All cultures to which sweet food has been introduced have readily consumed it and continue to do so
• In conclusion – we are ‘hard-wired’ to like sweet things, although the environment can modulate this somewhat (i.e., context)

Question 10

What 3 physiological effects does salt deprivation have?

Answer 10

• 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 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

Question 11

Do babies like salt?

Answer 11

• Babies may not be initially sensitive to salt
– 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

Question 12

What evidence do we have in humans that salt craving is under direct physiological control? (4)

Answer 12

– Adrenal tumour patient; altered kidneys capacity to retain salt, body loses salt, kid liked salty food
– Salt preferences peak in adolescence suggesting hormonal influence
– Salt ingestion (greater preference) in cold climates and blood pressure
– Exercise and salt preference (participants add more salt to soup for up to 12hrs after vigorous sweat-inducing exercise)

Question 13

How much salt do we need?

Answer 13

• 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

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)

Question 14

Can experience exert any effect over preference/liking for salt?

Answer 14

• 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

Question 15

Can babies taste bitter (and sour) and why?

Answer 15

• 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

Question 16

Can experience affect our liking of bitter tastes?

Answer 16

• Exposure does appear to affect preference for bitter foods, even if that preference is initially governed by our genes - for example
– The Aymara 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 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

Question 17

How does our production of lactase change with age?

Answer 17

• The ability to produce the enzyme necessary for digesting milk (lactase) is lost at the age of 2-3yrs in most humans
– 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

Question 18

How is lactase genetically controlled?

Answer 18

• The ability to produce lactase into adulthood appears to be genetically based
• There are two evolutionary arguments:
– In pastoralist societies a famine meant death unless you could digest milk
– 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
• 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
• Genetically, lactose tolerance is dominant, so it can spread fairly rapidly into new populations

Question 19

How does personality affect our food choices?

Answer 19

• Personality traits are quite strongly heritable
• 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

Question 20

What is the biological needs model for food choice?

Answer 20

• 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

Question 21

What is the evidence for “wisdom of the body”?

Answer 21

• 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
• Two major concerns have been raised about Davis’s work
– Modeling
• We know 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”

• 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

Question 22

What is the evidence against the “wisdom of the body”?

Answer 22

• 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

Question 23

What experiential factors affect our food choice? (3)

Answer 23

• 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
• Mechanisms that cause shorter-term changes in what we like (i.e., within a meal)

Question 24

How does neophobia affect our food choices?

Answer 24

• 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

Question 25

How can we conquer neophobia?

Answer 25

Mere exposure
• We prefer foods we are familiar with, so perhaps just mere exposure to an unfamiliar food might increase preference and liking
– Leaning that it is safe (explicitly or implicitly)
– Perceptual fluency (the ‘warm glow’ of the familiar)
• 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
• Thus unfamiliar foods can be introduced within the context of an already familiar flavour

Question 26

What are the 3 time frames of exposure?

Answer 26

– 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

– Very long-term (weeks)
• Monotony reduces liking
• This can also be important in advertising as some research suggests that over-exposure can breed dislike

Question 27

How do we learn likes? (4)

Answer 27

• 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
(2) Associating a food flavour with sweetness
(3) Medicine effect
(4) Drug-flavour learning

Question 28

How do we associate food flavours with calories?

Answer 28

• 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)

Question 29

How do we associate food flavour with sweetness? (3)

Answer 29

• 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

Question 30

What is the medicine effect?

Answer 30

• Associate flavour of a medicine with its power to make you feel better
– some animal evidence, but no convincing evidence in humans

Question 31

What is drug-flavour learning?

Answer 31

• 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)

Question 32

How do we learn dislikes?

Answer 32

– 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
– Can be persistent (but not unchangeable)
• But only because of reluctance to reconsume
– Occur irrespective of conscious awareness

Question 33

What is social learning?

Answer 33

• 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
• Babies tended to shift preference for juices dependent upon the preference of the carer
• 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

Question 34

How do social cognitive effects affect our food choices?

Answer 34

• 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

Question 35

How does advertising affect our food choices?

Answer 35

• Of all the forms of social learning TV advertising is by far the most potent, especially in children
• 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 and greater likelihood of purchase by the parent
• Food ads work

Question 36

How do we get from milk to adult-like food preferences? (4)

Answer 36

• 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