Food taboos

Question 1

What is the most powerful influence over what we eat?

Answer 1

The most powerful influence over what we eat is the culture in which we are raised
• Our culture defines for us all what is and what is not food

Question 2

What are food taboos?

Answer 2

• Nutritious and edible things that a culture does not tolerate as ‘food’ have been called ‘food taboos’

Question 3

What are the 3 categories of food taboos?

Answer 3

– Religious - many contain complex systems of prohibitions
• Islam (Halal vs Haram) & Jewish (Kashrut) – very similar
– Pork, monkey, dog, cat (omnivores & carnivores)
» Kashrut criteria for ‘kosher meat’ are a cloven hoof and chews cud
– Appropriate slaughter (to minimise suffering)
– Avoidance of blood products (contamination)
– Avoidance of carrion
– Limited sea food (scaly things only)
– No insects, except locusts
– The rules are complicated and conflicting, and many Islamic and Jewish scholars devote considerable energy to their interpretation
• Hinduism (Ahinsa - concept of non-violence)
– Around 30% of Hindu’s are lacto-vegetarians
» Mainly in India, location of most of the world’s vegetarians
– All universally avoid beef and all beef products

• Societal - Generally specific to a geographical region (and later to its diaspora)
– Pets are a good example
• Dogs (Korea/China)
• Roof hares (Cats in China)
• Horses (in France)
• Guinea pigs are widely eaten in Peru (around 65 million per year - see L from Cusco cathedral)

• Intra-cultural - Typically to women and children
– Handling of food during parts of the menstrual cycle
– Avoidance of specific foods during pregnancy (danger-related beliefs)
– Avoidance of specific foods during infancy (magical effects – small animals for small children)

Question 4

What are 9 theories of food taboos?

Answer 4

• Aesthetics - Taboo foods are just disgusting
– This may be a consequence not a cause (e.g. insects)
– It is a redescription of the phenomenon not an explanation
– We learn to be disgusted, we are not born that way

• Compassion - Avoidance of harm to animals
– Some specific taboos (notably meat) may have their basis in this
• Moral vegetarianism
– Characterised by disgust to meat and by its resistance to change (i.e., a value)
• Buddhism and Hinduism
– More complicated for Buddhists, where someone else can accrue the bad karma of killing (Buddha and rotten pork) – but all essentially about minimising harm
• Halal and kashrut slaughter
– Speed and painless death are the aims

• Divine commandment - Godly instructions
– Depends upon literalistic interpretation (unassailable)
– However, it is notable that every religious system with food rules has a lot of people arguing over how they should be interpreted
• For example, kashrut allows consumption of locusts. Some view this as a synonym for insect while others regard it as being specific to just locusts

• Ecology – Do not destroy your environment
– Food choices which are driven by ecological necessity which then become culturally enshrined
– This theory is quite promising and can offer an explanation for avoidance of pig and cow meat in particular environments and the presence of cannibalism in others

• Health and sanitation (e.g., Tapeworms)
– Avoidance of parasites and diseases
– Many pregnancy and child-related taboos claim to be of this type

• Ethnic identity – Food defines who you are
– Food styles tend to be resistant to change, along with taboos, and thus define you as a member of that culture – so important for a person’s sense of identity
– This may explain how they are preserved but it is not so good at explaining how they got started

• Natural law – It is just wrong to eat _____!
– A redescription rather than an explanation

• Self restraint/denial – A concept found in many religions
– Taboos result from denying immediate gratification or penance
– Easter (Ash Wednesday & Good Friday), Ramadan, Yom Kippur

• Sympathetic magic - You are what you eat
Strong association between particular types of food and particular aspects of personality and gender

Question 5

How is eating human flesh taboo? (3)

Answer 5

– In most countries it is not illegal
– It is not specifically prohibited in the bible
– Interestingly these may reflect the basic nature of our repulsion towards eating human flesh - it is so obvious and disgusting, it does not need to be said

Question 6

Is it risky eating human flesh? (3)

Answer 6

– Nutritional
• No - It offers all the same advantages of any meat

– Disease
• Blood borne diseases
– No difference in risk profile to eating bush meats (which are not risk free - SIV/HIV, 1930)
– HIV and Hep A & B can all be transmitted from dead bodies
• Prions
– A prion is an abnormal protein that once ingested causes other prion proteins in the body (especially the brain) to fold in a similarly abnormal way
– Humans can catch prion diseases from animals (BSE crisis in the UK, 1980s)
– And from eating people - Kuru (funeral ritual that involved eating dead relatives, with women & children getting the brain). This prion disease virtually exterminated the PNG Fore people between 1950-1970

• There is a risk… but no more so than with other meat

Question 7

Was eating human flesh always a taboo?

Answer 7

• Neolithic (C5000BC) cannibalism
– Many Neolithic sites have bone dumps
– These contain the remnants of the inhabitants meals
– These bone dumps also contain human bones
• Typically the same bones as with animals
– And importantly in the same proportions
• Same cut and stripping marks on the bones
• Same marrow extraction patterns
– Evidence from human coprolites containing human
myoglobin, point definitively to human flesh eating
• This evidence is important primarily as some anthropologists vehemently deny that anyone ever ate human flesh

Question 8

What did neolithic flesh eating result in?

Answer 8

• Balancing selection
– Evidence comes from genetic resistance to prion diseases
• There is a significantly higher than expected prevalence of the heterozygous form than of the two homozygous forms of a gene coding for the prion protein
• This is very unusual, as normally the homozygous forms would come to predominate
• The heterozygous form offers some protection against prion diseases (it delays onset until late in life)
• Rates of the heterozygous form are now very high in the Fore people
• The suggestion is that the higher than expected prevalence was driven by the selective advantage in heterozygotes who were able to eat human flesh without consequences for reproduction
• Crucially – rates are much higher of the heterozygous form in all human populations (relative to what would be expected), suggesting that cannibalism may once have been endemic in humans

Question 9

Regular consumption of human flesh has occurred under what five conditions?

Answer 9

– Cultural for food (Aztecs) –
– Famine for food (e.g., Cairo [12thC]; Leningrad siege WWII)
– Cultural funeral/war (e.g., Fore)
– Accident for food (e.g., Donner Party)
– Criminally insane (e.g., Albert Fish, Jeffrey Dahmer)

Question 10

How did the Aztecs eat human flesh?

Answer 10

• At the height of the Aztec empire, around 0.25M people/year were ritually sacrificed
• This is around 1% (per year) of the entire Meso-American population in the C14th
• There are many contemporary accounts from Cortes down
• The whole structure of their empire was built around providing a supply of non-Aztec flesh
• Most of these individuals were captured by raiding parties and then fattened in wooden cages prior to sacrifice
• The victims were taken to the top of the pyramids, had their heart cut out with an obsidian knife and then the carcass was rolled down the pyramid
• The body was then dismembered and the legs and arms were cooked and eaten, usually as a stew with chilli and tomato
• Unlike any other area of the earth Meso-america had no large game (except Llama/Alpaca) or domestic animals (except Guinea pigs – but not available in this location)
• The populace lived on maize, algae and beans
– This was a protein deficient diet
– It was also very vulnerable to famine
• It appears that institutionalised flesh eating arose as a direct consequence of this lack of protein, with the bodies of the sacrificial victims being used as a way of ensuring the loyalty of the Aztec warrior class to the King
– If you joined a raiding party and captured someone they were then yours to eat
– This could provide meat for you and your extended family
• There was an additional benefit
• During drought/famine more victims were needed to appease the angry gods (thus producing more food)
• Cortes and the Spanish conquistadores soon put a stop to
this and extinguished this remarkable meat-eating culture for ever
• Notice here how the unique ecological position of the Aztecs (general absence of farmed meat or hunted meat,
vulnerability to famine, and a diet deficient in protein) contributed to this unusual dietary pattern

Question 11

How does famine relate to eating human flesh?

Answer 11

• Although we know that people will engage in cannibalism under dire necessity, it is rare to find detailed accounts of this because it is usually seen as an aberration
• Yet there are instances in history where flesh eating has become widespread
• Such instances also tend to occur with a break down of social structures (i.e. law and order) and the Cairo famine of the 12th C is a good example

Question 12

What was the Cairo famine?

Answer 12

• Failure of the grain harvest on the Nile delta in 1201 led to one of the worst famines of the middle ages

Question 13

What was the Leningrad siege?

Answer 13

• A more contemporary example is the Nazi siege of Leningrad in WWII
• There were many instances of people eating dead bodies (around 300/month were caught and arrested), but far fewer of people actively killing to obtain ‘meat’ (around 50/month caught and arrested)
• Killing for ration cards was far more common

Question 14

Why do Muslims and Jews avoid eating pigs?

Answer 14

– Coprophagy? Pigs eat faeces, but then again so do cattle and chickens
– Tape worms? Pigs raised in hot arid climates in fact rarely transmit these parasites
– Other diseases? Sheep and cattle represent far more serious threats to health (via transmissible disease) than pigs, namely Anthrax & Brucellosis
• Anthrax is often lethal, Brucellosis is chronic but can have
unpleasant consequences

Question 15

What is an ecological explanation to not eat pigs?

Answer 15

• The only food available for pigs in hot arid climates is food also eaten by people
• If cultivatable land is limited, then pigs are in direct competition with us for food
• Better then to rely upon goats, cattle and sheep all of which eat grass - inedible to humans
• The argument is a simple one: Ecological necessity may in some, if not many instances, dictate practices which then become enculturated

Question 16

Why don’t some people eat cows?

Answer 16

– The notion here is of the need to protect (in India) both the main source of motive power and a very valuable protein source
– If you eat your cow in times of famine, then you will have no milk, nothing to pull your plough or to move your cart
– The animal can not be rendered ‘unclean’ like the pig, because contact with it is essential for farming, so instead it is deified

Question 17

Why do some people eat and some people don’t eat insects?

Answer 17

• Insect eating is approved in many cultures
– The bible sanctions the consumption of locusts, grasshoppers and beetles
– Around 80% of the world’s population currently consume insects from many different species
– We unknowingly eat about 0.5kg/yr
• Insect eating is generally precluded in Westernised countries, which may simply reflect the easy availability of rich protein sources from meat and dairy products
• It is interesting to speculate whether this will change if meat (as is likely) becomes progressively more expensive due to its environmental costs

Question 18

Vegetarianism in the West; Could a meat taboo emerge?

Answer 18

• Vegetarianism has a long history in Asia (India being home to 70% of the world’s vegetarians)
• In the west, moral vegetarianism is a British phenomenon
originating in the latter part of the 19th C
• It has since WWII gained considerable momentum

Question 19

Could meat become taboo for moral reasons?

Answer 19

• Many vegetarians do not like the idea of killing animals for food
• It would appear that this is primarily a moral choice, rather than one driven by ecology as we have argued for the other food taboos considered here
• But maybe not…
• Vegetarianism shares a considerable attitudinal overlap with ‘green politics’
• Indeed, the environmental and social impacts of mass meat production are considerable

Question 20

What are the impacts of meat production?

Answer 20

• It takes a lot of energy, vegetable matter and water to raise an animal for slaughter
• Animal production generates a lot of waste
• With a world to feed can we really afford to eat meat - indeed - if US grain was all diverted to feeding people an extra 800 million could be fed

Question 21

Why study what controls eating? (5)

Answer 21

– Encouraging healthy eating (i.e., consuming just enough)
– Management of obesity
• Assisting better approaches to dieting
• Understanding what leads to overconsumption
– Management of eating disorders
• Increasing food intake
– The food industry
• Keen to understand what makes us consume more
– The pharmaceutical industry
• Keen to understand the neurobiology of food intake regulation so it can develop drugs to target obesity

Question 22

What is hunger?

Answer 22

• Three key concepts are hunger, satiety and satiation
• Hunger has two scientific meanings
– (1) The subjective desire to eat
• This is primarily a psychological construct with some basis in physiology
• It has varied meanings that differ within and between people
– Stomach sensation of emptiness or related feelings
– Bodily weakness, headache – in fact just about any sensation you care to name will be identified by someone as indicative of their hunger state
– Desire to eat something ‘tasty’ (sometimes called hedonic hunger)
– (2) The objective state of the body when nutrient depleted
• There may be multiple signals for this

Question 23

What is satiation?

Answer 23

• Satiation is our loss of desire for food that occurs during an eating bout – and it has two meanings too
– It has a subjective meaning
• Reduction in pleasure from eating
• Increasing feeling of stomach fullness
– And an objective meaning
• This is reflected in multiple neural and hormonal signals that signal the intake of nutrients

Question 24

What is satiety?

Answer 24

• Satiety refers to the state after a meal
– This also has two meaning - the absence of a desire to eat (i.e., no hunger) and a physiological state reflecting the on-going digestion of nutrients

Question 25

How can we measure hunger and satiety? (4)

Answer 25

• Asking people whether they are hungry can be a rather poor predictor of how much they are likely to eat
– People may confuse arousal/anxiety/boredom for hunger
– There are individual differences in sensitivity to hunger
– While we believe that we eat when we are hungry, there is often only a weak correlation between eating and hunger
• Consequently most experimental studies of humans rely upon more objective measures
– Amount consumed
– Eating rate
– Food types selected
• In studies involving animals we can also measure the animals subjective hunger as well as using more objective measures such as those above

Question 26

What controls food intake? (5)

Answer 26

• The amount we eat could be hunger driven or satiety driven
• If meals are hunger driven, then the longer you are without food, the more you should eat at the next meal
• If meals are satiety driven, then the amount you ate at the last meal should predict what you will eat at the next
• Time blinded humans are satiety driven
• Caves study (no temporal cues at all)
• Suggests reliance on the way we feel (bigger meal – longer interval till next)
• When time cues are available we are hunger driven
• Suggests a significant cognitive component, that is an awareness of time elapsed since the last meal and the time the next meal is due
• Both contribute to intake control, but hunger driven eating may dominate

The control of food intake is very complex, there is no one theory but themes:
Biological controls of appetite (machine-like; may be controllable?)
– Psychological controls of appetite
• No free will - environmental factors that promote intake unconsciously
• Free will – the ability to exercise conscious control over food intake
– Central controls (CNS factors) – more biological focus
– Peripheral/environmental controls – more psychological focus

Question 27

What is short vs long term intake?

Answer 27

• We also have to consider a further issue
– Short-term energy needs (i.e., a meal)
– Long-term energy needs (i.e., maintaining our body weight)
• This is especially pertinent to small mammals
– A mouse has around 10% body fat, enough to sustain it for around 2 days without food
• If it stores more fat, then it becomes less agile and is easier to catch
• If it stores too little fat, it becomes vulnerable to food shortages
• Thus the mouse has to carefully manage short-term (immediate) and long-term needs – too fat it gets eaten, too thin it starves
– The same is also true for humans and by and large we are fairly good at this - but not perfect…
• Different mechanisms control long-term and short-term energy needs

Question 28

What are the 13 peripheral factors that control food intake?

Answer 28

Contractions
Cues
Portion size
Variety
Accessibility
Time
Temperature
Season
People
Distraction
Mouth
Guts
Digestion

Question 29

How do stomach contractions control food intake?

Answer 29

For many people a rumbling stomach is a sure sign that you are hungry
• The basic rationale here is that an empty stomach produces contractions which then cause hunger (which prompts eating)
• Filling the stomach stops the contractions and thus eliminates the desire to eat
– Washburn had a tube and balloon put in his stomach and then partly inflated to measure stomach contractions
– His reports of hunger peaked at the height of a stomach contraction
– Similar findings were obtained in other people
– As there were no contractions when participants were not hungry and because the contractions started before people reported feeling hungry, they concluded that stomach contractions caused hunger

• People without a stomach can and do feel hungry
• People who have had gastric banding (for morbid obesity)
and who also have a ‘tiny’ stomach also feel hungry
• More sensitive and less invasive measurement techniques
reveal only a weak relationship between stomach contractions and hunger
– Some people seem able to detect stomach contractions (which do occur in an empty stomach) while others can not
• Stomach contractions are a signal that the stomach is
empty, similar to a dry mouth and thirst

Question 30

How do environmental cues affect food intake?

Answer 30

• Environmental cues associated with food can trigger hunger
• These can be sounds, smells or sights
• Indeed we are almost constantly exposed to cues to food
• If they do influence our behaviour then this may be very important in triggering (over) eating
– Cues work via associative learning between the cue and prior episodes of ingestion (i.e., to pleasure and/or energy)
– This is directly analogous to Pavlov’s famous classical conditioning experiments with dogs
– A bell occurred prior to the delivery of food and this came to elicit an anticipatory response
• Salivation (and hunger)
• Insulin release, lower blood sugar (and hunger)

Question 31

How does portion size affect food intake?

Answer 31

• The amount of food on your plate or in your serve will significantly influence how much you eat
• Portion size influences the amount you eat unconsciously and having a slightly smaller plate at home is a simple step to reducing intake
• The same effect can also be observed with larger packets of food, which lead to larger serves
• Portion sizes have relentlessly increased in recent years

Question 32

How does variety of food affect food intake?

Answer 32

• The greater the choice of foods available, the more one will typically eat
• There are some obvious and not so obvious reasons for this
– An important one is sensory specific satiety
• It is easy to get sated on a single food, but hard with multiple foods
– More choice makes it more likely that your favourite food will be represented
– More choice is often associated with other factors that are known to promote intake (lots of people, excitement, alcohol)

Question 33

How does accessibility affect food intake?

Answer 33

• Making food more accessible increases consumption
– Within a room, the greater the distance between you and a plate of snack food, the less you will eat
– Moving foods in a cafeteria, so that ice creams are equally visible, but more distant from the serving line, decreases their consumption
– In salad bar displays, items at the edge are eaten more frequently than items in the middle or back
– Fewer food items are eaten if they have to be picked up by tongs rather than with a spoon
• In a nutshell we are lazy, and we will readily eat more if no
extra effort is needed to obtain that food

Question 34

How does time affect food intake?

Answer 34

• Time as a cue to eating
– People and animals can learn to expect food after a particular delay, so the passage of time can become a cue to the need to eat
– Perhaps more importantly, we all have access to clocks, and we have learnt as children to expect meals/snacks to occur at rather specific times in the day
– These ‘eating times’ are to some extent social constructs
• Meal times have changed historically, driven by artificial light and work requirements
• Hunter gatherers exhibit a range of eating behaviours from large single meals (on a given day with no further intake) to grazing (smalls amounts of food as it is found)
• Rats (in the lab) can also readily adapt to all sorts of food presentation patterns
– Clock regulated meals/snacks may have its pros and cons
• CON: Eating when not hungry because it is a ‘meal time’
• PRO: May be hard to track food intake if eating is irregular

• Evidence for time-related control of food intake
– Multiple diary studies indicate that meal sizes increase and intermeal intervals (250 mins vs 150 mins) decrease across the course of a day in American participants
– Jet lag - hungry at inappropriate times, not-hungry at appropriate times (interaction of habit and circadian rhythms)
– Night eating syndrome
• Product of a phase delay in a persons circadian rhythm
• Consume 25% of calories after evening meal, with night-time waking, hunger and eating
• Very common in obese individuals and heritable too

Question 35

How does temperature affect food intake?

Answer 35

• Ambient temperature and temperature regulation have been suggested to affect appetite
• Body temperature drops, you become hungry, eat and dietary thermogenesis (i.e. metabolising the food) boosts body temperature reducing hunger
• Evidence?
– Food shifts more quickly from the stomach to the gut when you are cold
– People in cold climates eat more calories (as do animals kept in cooled environments)
– Hotter ambient temperatures reduce intake
– Lower blood glucose (which induces hunger) also results in lower body temperature (and hunger)

Question 36

How does the season affect food intake?

Answer 36

A drop in ambient temperature or shortening days might prompt increased ingestion as a way to prepare for winter
• At least in the past winter would have been a time for high energy needs but low food availability
• In long-term studies of food-intake in American’s the amount of food consumed consistently increases in the fall

Question 37

How do people affect food intake?

Answer 37

• Essentially the finding is that the more people there are the more food gets consumed per person
• Social facilitation effects are most pronounced for family members, then friends, but also work for strangers
• They are no gender effects (overall) but when a man and a woman eat together, the woman will tend to eat more than she would alone, whilst the man eats a similar amount as normal
• This effect may be moderated by romantic context
• They occur for any type of meal or snack
• They occur in many other organisms as well as people
• In humans, they appear to be primarily the result of
– The greater amount of food available at social events
– Longer time spent at the table, so more nibbling
– Distraction, resulting in eating more, because of chatting
– Disinhibition (having a good time)

Question 38

How does distraction affect food intake?

Answer 38

• Television viewing (TV) has several effects on food intake
• Many people eat while watching TV
– This can increase food intake via many of the same mechanisms as for social facilitation
– The effects on food intake are most pronounced if the TV show is moderately distracting
• Just sitting watching TV can trigger eating
• This can occur via associative learning (i.e., from prior eating with TV), from adverts, or from show content (cookery shows etc)
• Eating with TV can also have delayed effects
– If you eat say a snack with TV, and later have lunch, you will eat more at lunch than if you had eaten that snack without TV
– TV distracts you and makes it harder to remember what you have eaten

Question 39

How does the mouth affect food intake? (4)

Answer 39

• A further factor in peripheral control of eating is the mouth
– The role of the mouth (i.e., sensory factors) in controlling intake has been extensively investigated in animals
– The basic idea is to see how much the animal will eat if food intake is just controlled by the mouth
– To test this a hole is made in the oesophagus so that food comes out at this point, a procedure called Sham Feeding
• What happens when the animal is allowed to eat?
– They eat far more than normal, but do eventually stop
– How might the mouth affect eating?
– The principal mechanism here is one we have already examined – sensory specific satiety

• What about the taste of the food?
– Sweet foods are consumed in greater quantities than non-sweet foods, even when matched for calories
• Insulin mechanism (insulin secreted when sweet taste is sampled, lowers blood sugar and increases hunger)
• Differential storage (body assumes sweet = higher calories, so more is eaten because the body can store the surplus calories for a ‘rainy day’)

Question 40

How do the guts affect food intake? (4)

Answer 40

• Inflating a balloon in the stomach has no effect on sham feeding, except where the balloon is very very expanded
• Putting food directly into the stomach does reduce sham feeding, even if there is a pyloric cuff
• The nutrient density (and fibre content) of food placed directly in the stomach does hasten satiety
• These effects are probably mediated by the vagus and splenic nerves, as these stomach signals are reduced by damage to these nerves

Question 41

How does digestion affect food intake?

Answer 41

• When food is broken down in the stomach and gut, a range of chemicals are released into the bloodstream
• These come from the food, the bodies response to the food and from the chemicals that the body utilises to digest it
• These turn out to be some of the most promising candidates for controlling the termination of a meal