Lecture9+10.pdf

Food Taboos • Appetite: The psychology of eating and drinking 1 1 Introduction • There are, as we have seen, many causes of individual differences in food choice • Perhaps the most powerful influence over what we eat is the culture in which we are raised • Our culture defines for us all what is a...

Food Taboos • Appetite: The psychology of eating and drinking 1 1 Introduction • There are, as we have seen, many causes of individual differences in food choice • Perhaps 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 • The aim of today's lecture is to examine how this might occur by examining some specific examples 2 2 Food taboos • Nutritious and edible things that a culture does not tolerate as‘food’ have been called‘food taboos’ • Taboo derives from the Polynesian concept of to “set-apart” • We will start by looking briefly at theories of food taboos and who they apply to • We will then examine four specific examples – Human flesh (currently universally pervasive) – Pigs (in Jewish and Muslim cultures) – Cows (in Hindu culture) – Insects (currently pervasive in Western cultures) • Finally, we will look at ‘becoming a vegetarian’ as this reflects two key aspects of food taboos in general – Initiation (how a taboo gets started) – Moralisation (how an attitude gets turned into a value [i.e., taboo-like]) 3 3 Taboos - general • Food taboos fall into three general categories – 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 4 4 Taboos - general • 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) 5 5 Theories of Food Taboos - 1 • 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 6 6 Theories of Food Taboos - 2 • 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 7 7 Theories of Food Taboos - 3 • 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 – Fictitious tribe experiment in US, Turtle eaters and Wild Boar eaters • Turtle eating tribe judged to be good swimmers and long lived • Wild boar eating tribe judged to be good runners and heavily built • Taboos shaped by symbolic resemblances – red meat and masculinity, vegetarianism and femininity 8 8 Taboos - Eating human flesh • The first question we have to ask is whether people in general do regard eating human flesh as ‘disgusting’ and ‘diabolical’ - well do they? – In most countries it is not illegal • Germany, Armin Meiwes & Bernd-Juergen Brandes; the former’s conviction initially being for manslaughter (murder only on his re-trial) – It is not specifically prohibited in the bible • The Catholic church spoke in favour of the Andes survivors – 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 9 9 Is it risky eating human flesh? • Is there any obvious reason why it is a bad idea? – 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 10 10 Was it always taboo? • 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 11 11 Fillet Skinning Dismember Note similar proportions for animal and human bones… 12 12 Neolithic flesh eating • Balancing selection – Evidence comes from genetic resistance to prion diseases • There is a significantly higher than expected prevalence of the heterozygous form (i.e. Aa) than of the two homozygous forms (i.e. aa, AA) of a gene coding for the prion protein • This is very unusual, as normally the aa or AA (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 13 13 Regular consumption • Regular consumption of human flesh has occurred under five conditions – Cultural for food (Aztecs) – • At its height up to 250,000/year – – – – 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) • We will examine the first and second, as these are most pertinent to the lecture 14 14 Aztecs I • • • • • 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 (see below) 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 “I must now tell how in this town we found wooden cages made of lattice-work in which men and women were imprisoned and fed until they were fat enough to be sacrificed and eaten. We broke open and destroyed these prisons and set free the Indians who were in them. But the poor creatures did not dare run away. However, they kept close to us and escaped with their lives. From now on, whenever we entered a town our captain’s first order was to break down the cages and release the prisoners, for these cages existed throughout the country. When Cortes saw the great cruelty he showed the chiefs of the town how indignant he was and scolded them so furiously that they promised not to kill and eat anymore Indians in this way. But I wondered what use all these promises were, for as soon as we turned our heads, they resumed their old cruelties.” Diaz, 1520 15 15 Aztecs II • 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 • Why had this systematic flesh eating arisen? 16 16 Aztecs III • 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 17 17 Aztecs IV • 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 18 18 Famine and meat • 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 • This famine was also recorded in some detail too 19 19 The Cairo famine • Failure of the grain harvest on the Nile delta in 1201 led to one of the worst famines of the middle ages • The famine was recorded by Abd al-Latif an Iraqi doctor who practiced medicine there • The following are quotes taken directly from his description of events which ensued in the year of the famine… 20 20 Abd al-Latif I • ‘I saw one day a women with a head wound being dragged through the market. They had seized her while she was eating a small roast child. The people in the market paid not the slightest attention… for they had become so accustomed to such sights’ • ‘The children of the poor, those who were young or had no one to care for them were scattered all through the town. Men and women alike lay in wait for these unhappy children, carried them off and ate them’ • ‘This mania for eating people became so common among the poor that the majority of them perished in this way’ 21 21 Abd al-Latif II • ‘A colleague of mine was approached by a man to accompany him to the home of an invalid. He allowed himself to be taken into the entry of a half ruined house but the look of the place alarmed him, he stopped on the stairs whilst his companion went ahead. As he did so he heard the man’s crony say “after taking so long have you at least brought some good game?”. These words struck terror in the doctors heart and he managed to flee’ • ‘This hideous calamity I have just described struck the whole of Egypt. There was not a single spot where eating people was not common’ 22 22 Leningrad siege 1941-1944 • 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 23 23 Cannibalism conclusion • Our aversion to human flesh (women and children being most tasty - reportedly “beef like”) is, it appears, culturally sanctioned • When the culture embraces its consumption (arguably for ecological reasons in the case of the Aztecs) or when hunger dominates and there are no cultural restraints, many people indulge • What about other food taboos - do these have an ecological basis too? 24 24 Pigs, Cows & Insects • Pigs - Why do Muslims and Jews avoid eating this animal? – 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 • Could the explanation be more prosaic? 25 25 Pigs – an ecological explanation • 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 26 26 Cows • Similar arguments can be used to explain avoidance of eating cows’ flesh – 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 27 27 Insects • 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 • In Northern Italy children eat sweet moths • In Sardinia they eat cheese with live maggots in it – We unknowingly eat about 0.5kg/yr • Peanut butter, flour and noodles • 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 28 28 Vegetarianism in the West Could a meat taboo emerge? • 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 – – – – In the US 3.2% are vegetarian or vegan (about 10 million people) In Europe this varies from 2-4% of the adult population In Australia it is similar at around 3% These figures increase markedly if you ask about reducing meat intake, choosing vegetarian dishes or contemplating a vegetarian diet (in all of these cases between 10-25% endorsement) • Why? 29 29 Moral? • 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 30 30 Impacts of meat production - 1 • It takes a lot of energy, vegetable matter and water to raise an animal for slaughter – Oil input to produce beef is 10 times that for producing an equivalent amount of wheat – 50% of US water supply goes to animal production – 80% of agricultural land in the US is for animal production – 90% of the US soy crop, 80% of the corn crop and 70% of the wheat crop goes to animal production 31 31 Impacts of meat production - 2 • Animal production generates a lot of waste • 20% of US methane (a potent greenhouse gas) emissions come from animal production • The US National Academy of Sciences and the US Public Health Association say “Pollution from massive animal factories jeopardise health in rural communities. Bearing no resemblance to a traditional farm, packing 1000’s of animals into a small space, they produce as much waste as a small city” • 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 • Is vegetarianism simply the start of a major social change in our attitudes to meat based upon its ecological costs? • Could meat in general become a new taboo? 32 32 Conclusion • Food taboos occur in all cultures • They offer a very powerful means of controlling what we may and may not eat • A good (but not the only) explanation of the origin of food taboos is that they develop as a consequence of ecological forces operating within a society • We will return to the social impacts of our dietary choices later in the course, as they have a major bearing upon the study of obesity… 33 33 Starting and stopping eating 1 Based upon Logue Ch.2 Appetite: The psychology of eating and drinking 34 34 Introduction • Why study what controls eating? – 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 35 35 Hunger • 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 as we will see 36 36 Satiation and Satiety • 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 • 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 37 37 Measuring hunger and satiety • 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 38 38 What controls food intake? • 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 39 39 Short vs long-term intake • 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… • We might expect that different mechanisms control long-term and short-term energy needs and as we will see they do 40 40 So what controls food intake? • The control of eating, as you will see, is very complex • Thirst, which only has one key stimulus - water - still utilises multiple mechanisms and food is a far more complex stimulus • Do not expect any grand theory - there is not one • However, there are three important and recurring themes, which I will return to later, but look out for them as we go on – 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 • To organise this material, I have broadly followed Logue… – Central controls (CNS factors) – more biological focus – Peripheral/environmental controls – more psychological focus 41 41 Peripheral factors – Contractions I • This is a good place to start both historically and because 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 • So do stomach contractions cause hunger? – 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 42 42 The equipment 43 43 Peripheral factors – Contractions II • How does Cannon & Washburn’s (1912) theory stand up today? • Well 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 44 44 Peripheral factors – Cues I • Environmental cues associated with food can trigger hunger • These can be sounds (e.g., cooking), smells (e.g., wafting from a bakery) or sights (e.g., pictures in a cook book, a logo) • Indeed we are almost constantly exposed to cues to food (e.g., adverts, food-related symbols, kiosks, cafes, vending machines etc etc) • If they do influence our behaviour then this may be very important in triggering (over) eating 45 45 Peripheral factors – Cues II • How might such cues work? – Probably 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) • The real problem is in establishing at what level environmental food cues actually affect our behaviour – Are we aware that they can make us hungry? – Are we aware that this hunger then drives eating behaviour? 46 46 Peripheral factors – Portion size • 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 (see accompanying graph) 47 47 Peripheral factors - Variety • 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 that we encountered in a previous lecture and that we will come across again today 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) 48 48 Peripheral factors - Accessibility • 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 49 49 Peripheral factors – Time I • 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 50 50 Peripheral factors – Time II • 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 – – – – Morning 400 Kcal/meal Afternoon 600 Kcal/meal Evening 700 Kcal/meal This corresponds to what all of us may recognise as a smallish breakfast, somewhat larger lunch, and a larger evening meal – 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 51 51 Peripheral factors - Temperature • 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) 52 52 Peripheral factors - Season • Do people eat more when winter approaches? • We might expect that either the 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 53 53 Peripheral factors – People I • The most consistently powerful peripheral factors identified in promoting food intake is the number of people present when eating • Essentially the finding is that the more people there are the more food gets consumed per person 54 54 Peripheral factors – People II • 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) 55 55 Peripheral factors - Distraction • 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 56 56 Peripheral factors – Mouth I • 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 57 57 Peripheral factors – Mouth II • 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’) 58 58 Peripheral factors - Guts • What about the stomach and the intestine? • Their respective roles (especially in stopping eating) have also been explored using oesophagotmised animals, typically dogs or rats • They employ a technique called intragastric feeding, in which food is placed directly in the stomach or the gut • So what effect does this have on sham feeding (in other words how hungry or sated does this make the animal feel)? 59 59 Peripheral factors - Guts • 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 60 60 Peripheral factors - Digestion • What about the process of digestion? - 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 and we will examine these in the next lecture 61 61