Eating Behaviour

1. Familiarity and Learning

Birch & Marlin (82) found that exposure of 2 year olds to a new food over a 6 week period increased preference for that food.  A minimum of 8-10 exposures were needed for the initial dislike (neophobia = avoidance of unfamiliar foods) to change to a preference.  The children learn that the food is safe.

Mothers usually provide most food to a child therefore it makes sense that their attitude to foods will affect the child’s preferences.  Ogden (2007) found a positive correlation between mother’s and children’s diets.  Children are also exposed to their peers eating behaviours and widespread advertising. 

Parents often use OPERANT CONDITIONING (learning through rewards and punishment) to change a child’s eating behaviour.

Why might a bout of gastroenteritis stop a person from eating mussels ever again?
You have a bad experience, which is essentially a punishment. This makes you learn not to eat this food again as it will make you ill. This is called taste aversion
Often parents encourage the eating of disliked foods with the promise of a desired food later.  E.g. ‘if you eat all your broccoli you can have pudding’.

...presented 28 children with a story involving imaginary foods – hupe and hule.

Condition 1: half the children were told a story in which a mother tells her child they can have hupe then hule or hule then hupe (counterbalanced). This was the non-contingent condition (ie having one food is not contingent on first having the other).

Condition 2: In the other condition, half the children were told a story in which a mother tells her child they can have hupe IF you eat hule or they can have hupe if they eat hule (again, counterbalanced). This is the contingent condition (ie having one food is contingent on first having the other).

All the children were then asked which food they would prefer to have.

The findings were that there was no preference in the non-contingent condition. However, in the contingent condition children expressed a preference for the food that had been used as a reward for eating the other food.

In addition, children rated their preferred food choice as tasting better. So, if the story involved the mother telling her child you can have hule if you first eat hupe, the children said they would prefer to have hule themselves and that it tasted better than hupe, even though they've never eaten it.

How does this study support operant conditioning in eating behaviour?

It suggests that children learn through rewards as they show that they have a preference for the food used as a reward. 

Strengths:

• High internal validity
• they’ve counterbalanced and used fake food names to eliminate a preference for a sound or a food
• cause and effect can be established,

Weaknesses:

• small sample so harder to generalise to the whole population

What is Social Learning Theory?

Learning behaviour through role models

Who are the role models in a child’s life?

Their mother and father, and their peers and celebrities 

How do they need to behave to help a child make good eating choices?

Balanced diet, kids would then imitate that

What is vicarious reinforcement? 

Where you witness your role model being rewarded for their eating choices

Duncker (1938) looked at social suggestion on children’s food choices.  Children observed a series of role models making food choices – mother, unknown adult, fictional hero, a friend and a child.

The greatest food preference CHANGE was on the children exposed to an older child, a friend, their mother or the fictional hero.  They were most likely to eat an unfamiliar food if they had seen their mother do it.  

Therefore parental behaviour is essential part of process of social learning with regard to the acquisition of eating behaviours.

In different parts of the world children grow up to have different attitudes towards foods.  So children in the UK think chips, sweets, nuggets and pizza are all treats and tasty.  In India they grow up thinking that spicier food tastes better and in Japan children prefer a fish based diet.

Wardle et al (1997) surveyed 16000 young adults in 21 European countries asking about their diet.  They found that males were less likely to be eating a basic healthy diet.  They also found differences between countries:

• In Sweden, Norway and Denmark most fibre was eaten
• In Italy, Portugal and Spain least fibre was eaten but they ate most fruit
• Those in England and Scotland ate least fruit
• Those in Poland and Portugal had the highest salt intake and it was lowest in Sweden and Finland.

In general those on a ‘Mediterranean diet’  have lower levels of heart disease and obesity than in other European countries.  This may be due to lower levels of processed food and more natural products being used.

Weaknesses: Eurocentric; Survey – social desirability bias,Only young adults

Strengths: Large sample size;Ethical

Lesham (2009) compared the diets of two different ethnic communities in Israel who lived in the same area and had equal access to shops and food.  In the Muslim community the carbohydrate intake was twice as high as the Christian group.  Muslims also ate more protein, fats and salt.  But mean BMI was the same.

Lesham felt this was because previously to all living in same area they had lived in different environments.  Some may have previously been from Bedouin communities so needed a high salt intake.  There are also strict religious reasons for eating or avoiding specific foods

There also may be socio-economic factors that vary between cultures or sub-cultures.  Income, education level and food knowledge vary between culture groups and all impact on eating behaviour.

Education

Xie et al (2003) Adolescents whose parents were more educated had higher intake of carbohydrate, protein, fibre, vitamin A and calcium.  They were also more likely to consume more fruit and vegetables.

Income

Cost of food is a significant factor in food choices.  People from lower socio-economic groups tend to have lower income and therefore it has been found they are more likely to have an unbalanced/unhealthy diet.  Travelling to shops also cost more money so people may be limited geographically when making food choices as well.

Xie et al (2003) Children from higher income families had greater intake of polyunsaturated fats, protein, calcium and iron.  They also had more dairy products.

Their peers from lower socio-economic groups had diets that had higher intake of meat, full fat milk, fats, sugar, potatoes and cereals combined with lower levels of fruit, brown bread and vegetables.

Hunger makes us feel more vigilant, irritable and aroused, but after we have eaten we feel satisfied, sleepy and calm (all pleasurable).  Most people find sweet tastes pleasurable and it is known that sweet tastes calm down babies. 

There are two biological reasons for this:

Serotonin Hypothesis: Carbohydrates such as  chocolate contain  an amino acid called tryptophan, this is used in the brain to make the neurotransmitter serotonin.  Low levels of serotonin are linked to depression.  So eating sweet things makes people’s mood more positive. This is unlikely as pure carbohydrate is needed – which is very rare. Opiate hypothesis: In the brain there are opiate neurotransmitters, e.g. enkephalin which are also known as endorphins.  These are addictive and lead to feelings of euphoria.  Therefore the brain’s opiate pathways are part of our reward system which control our feelings of pleasure and reward. There is evidence that opiates are linked to feeding behaviour.  E.g. blocking the endorphin brain system using drugs reduces food intake and reduces thoughts about food.

Comfort foods make us feel comfort and pleasure.

We also may have food cravings – when we really want a specific food.  These may reflect the need for variety in our diets; it may be that our body needs nutrients or calories and these then affect our choice of food.  

Women more commonly report food cravings than men, often during the pre-menstrual phase and during pregnancy.

Affective states are different moods.  Garg et al (2007) looked at how these influence food consumption.  They found that sad people consider pleasurable products (eg chocolate, popcorn) as mood-uplifting and therefore over-consume them

Aim/Hypothesis – To examine how manipulating happiness and sadness through the content of a movie can influence the consumption of hedonistic foods such as buttered popcorn.  It is expected that sad people will attempt to repair their negative mood state, leading them to consume more than happy people.

Method – P’s watch full length movies that evoked either a positive or negative effects.  They were told that during the 2 day study the researchers would be asking them to evaluate the films.  

Sad state film = Love Story

Happy state = Sweet Home Alabama

Films were selected because they could be matched on several key variables, such as running time, quality (critic rating), box office success and broad content area. 

Day 1 – P’s randomly assigned to one of two viewing rooms (these were designed to look like living rooms) where 5 – 8 P’s watched the movie together.  They were given equal amounts of popcorn and calorie free drinks.  About 180 grams of popcorn each.  At the end of the film P’s were asked to assess the movie (1= sad and 9= happy) at the end.  They also rated their mood and had to say what it was about the film that made them feel happy or sad.  The popcorn container was weighed and amount consumed was calculated.

Results – Movies were successful in manipulating the desired emotions.  Also P’s consumed significantly more (28% more) while watching the sad film than while watching the happy movie

What research method has been used?

Lab experiment

Give three examples of how the researchers controlled confounding variables.

Length of movie, quality (critic rating), box office success

What are the IV and DV?

IV = emotion state of film. DV= amount of popcorn eaten

What is the conclusion?

The more unhappy you are, the more you will eat. The happier you are you are, you don’t need to eat as much (youre trying to activate the opiate pathway)

Weaknesses:

• Gender bias – majority of research is carried out on females
• Focus on nurture; Familiarity and learning suggests nurture is the primary cause of food preferences. Whereas mood and food suggest biology determines your eating behaviour (nature)
• There is no free will; behaviour is either learn passively or a result of biology is predetermined

Weaknesses:

• Gender bias – majority of research is carried out on females
• Focus on nurture; Familiarity and learning suggests nurture is the primary cause of food preferences. Whereas mood and food suggest biology determines your eating behaviour (nature)
• There is no free will; behaviour is either learn passively or a result of biology is predetermined

Boundary Model (Herman and Polivy, 1984):

This model tries to explain why dieting can lead to overeating.  Dieters set themselves a boundary (e.g. 1500 calories per day) and try to eat within this limit.  However on occasion they may go over their boundary and will then binge until they are full.

Supporting study – Wardle and Beales (1988)

Investigated whether dieting resulted in overeating

27 obese women were placed in three groups and monitored for 7 weeks.

• Diet group – end up eating more
• Exercise group
• Control group

During the study they did lab experiments designed to test their food intake.  They found that participants in the diet group ate more than other 2 groups.  

Why does this study support the Boundary Model?

Because they exceed the cognitive boundary and then binge and over eat

Strengths:

• Lab experiment, well controlled, high internal validity 

Weaknesses:

• They didn’t take into account extraneous variables
• Sample size – low representativeness
• Gender bias, all women, low population validity
• Artificial settings, hawthorne effect

a way of investigating the causes and consequences of dieting (AKA restrained eating) and suggests that dieting can be successful (resulting in weight loss) or unsuccessful (leading to weight gain and overeating).

I.e.  If one is restraining one’s eating one should then eat less.  BUT it has been found that restrained eating can lead to both under and over eating.

 Supporting study - Herman and Mack (1975)

Herman and Mack compared dieters (restrained eaters) with non dieters (unrestrained eaters) using the preload/taste-test method - 45 female students

3 conditions:

1. No preload(no milkshake)

2. Low calorie preload(low calorie milkshake)

3. High calorie preload (2 milkshakes)

After eating it participants were told they were going to do a taste preference test, in which they were given a number of different types of food.  P’s were left alone to do the taste-test.  The DV is how much of the taste-test food they ate (P’s weren’t aware this was being measured).

Overall non-dieters (unrestrained) compensated for high calorie pre-load by eating less on the taste-test.  BUT dieters (restrained eaters) ate more on the taste-test if they had had a high calorie pre-load.

It could be because of disinhibition (eating more as a result of the restraints being loosened).  A kind of ‘what the hell’ attitude – they have already broken their diet so they may as well make the most of it.

Strengths:

• because they didn’t know, no social desirability bias/hawthorne effect, won’t mind about eating alot, won’t think they’re ‘fat’
• High internal validity

Weaknesses:

• They didn’t know the true aims of the test – unethical because no fully informed consent
• Gender bias
• Small amount of participants, low pop validity

Ogden & Hills (2008) carried out interviews with successful dieters and found 4 long term factors that they had in common. 

1. Hold a model of obesity that focuses on behaviour as central to their weight problem (behavioural model)

2. avoid state of denial whereby they want to eat but do not

3. create a situation where food is no longer regarded as rewarding

4. establish a new identity as a thinner, healthier person

In addition, Powell, Calvin and Calvin have suggested that dieting can also be successful when combined with other lifestyle changes:

• physical exercise

• group and individual support

• monitor own progress to increase self control

Ogden - the theory of ironic processes of mental control (2003) also found that the more people try to forget about the forbidden desired food the more they found themselves thinking about it (being preoccupied).  This is supported by Wegner et al (1987) who asked P’s not to think of a white bear but ring the bell if they did.  Those P’s rang the bell more often that those who were specifically told to think about the white bear.

Redden:

• The secret to successful dieting lies in the attention we pay to what we are eating
• People like experiences less as they repeat them, therefore the restrictive nature of a diet would soon get boring
• Redden believes we should focus on the details of the meal; changing the details of the salad. Prawn cocktail, Caesar salad
• He gave 135 participants given 22 jelly beans
• In group one, general information given, gave them jelly beans individually with boringness ‘bean number 5’
• In group two he gave specific information, like ‘cherry flavoured bean number 7’ or ‘lemon flavoured jelly bean number 4’
• Participants got bored with eating beans faster if they saw the general information and enjoyed the task more with specific info.

Weaknesses of these studies:

• Gender bias – mostly females used
• Culture bias – mostly American participants used

Key Terms:

Neural: linked to the nervous system and brain

Satiation: feeling full and no longer hungry

Hypothalamus: part of the mid brain associated with hunger and satiation 

Hormone: chemical released by a gland that travels around the body via the blood stream

Metabolic rate: speed at which the body uses stored energy 

Homeostasis: maintenance of a constant internal environment e.g. try to keep body temp at 98 degrees Fahrenheit in various ways 

To maintain a healthy body weight we have to regulate our eating behaviour and food intake.  Our brain has to decide all the time whether we are hungry or sated (full) or somewhere in between.

How does your brain do this?  Where can it get information from?

 Stomach, blood, hypothalamus, external things like food

In 1912 Cannon and Washburn carried out a very bizarre study where Washburn swallowed a deflated balloon.

This was then inflated and used to measure stomach contractions in relation to Washburn’s feelings of hunger.  They were experimenting to see if the presence of food (inflated balloon) was linked to people feeling hungry or sated.  He felt hungry when the balloon was flat . When

the stomach muscles ( stretch receptors ) being stretched sent a signal to the brain basically saying ‘we’re hungry’.  

The problem with this was that people who had had part or all their stomach removed because of cancer were still able to control their food intake.  So the stomach is important but not the only thing that regulate food intake.

Aside from whether the stomach is full or not there are also other ways the stomach is related to controlling eating.  A hormone called ghrelin is secreted by the stomach, which is directly proportional to how empty it is.  I.e. as the time passes from the last time we ate we feel hungrier.

 If you inject people with ghrelin they increase food intake and body weight.  Ghrelin signals the hypothalamus to start eating.

They looked at blood ghrelin level changes over time between meals.  6 P’s ate lunch then had their ghrelin levels measured every 5 minutes using blood tests (tube or catheter was inserted into vein).  P’s assessed their hunger every 30 minutes.  This carried on until the P requested their evening meal.

They found that ghrelin levels fell immediately after lunch to their lowest level at about 70 minutes.  They then slowly rose, peaking when P’s requested evening meals.  5/6 P’s ghrelin levels were closely correlated with degree of hunger reported.  Supporting the idea that ghrelin is a key appetite signal in humans.

High internal validity, small sample, low population validity

Ghrelin signals that you should start eating whereas leptin signals your brain to stop you eating.  Therefore leptin is an appetite suppressing hormone but it is quite long term.

Another hormone that has the opposite effect to ghrelin is CCK. This is produced by the small intestine once food has passed through the stomach and it stops you feeling hungry and it also stops the stomach from producing any more acid.  If injected into rats it causes weight loss.  But animals with a genetic mutation that eliminates the CCK system become obese.

This area of the brain is associated with feeding.  There are a number of ways research has been carried out to find out if this area is linked to feeding.

1.  Lesions to hypothalamus of animals

2.  Investigate the changes in feeding after damage to specific sites in brain

3. Effects of neurotransmitters introduced into specific brain areas

4. Impact of drugs on parts of brain

5. Use of functional magnetic resonance imaging (fMRI)

Originally the 2 parts of the hypothalamus were linked to two different aspects:

Lateral Hypothalamus (LH) = feeding centre (makes you eat)

Ventromedial hypothalamus (VMH) =safety centre(not hungry)

Lateral Hypothalamus; Anand & Brobeck:

Found that a lesion in the lateral hypothalamus in rats caused a loss of feeding behaviour known as aphagia. Stopped eating even in the presence of food.

Ventromedial Hypothalamus; Hetherington & Ranson:

Rats over-ate and become dramatically obese, known as hyperphagic rats.

All behaviour according to evolutionary psychologists is ADAPTIVE – benefits us and our survival chances.  The problem is that evolution is very slow and has not caught up with the modern world.  So some behaviour that now appears to be MALADAPTIVE has to be analysed and understood as being adaptive in the past.

Evolution theory states that natural selection is the process by which all humans (in fact all species) evolve.  This means that only those characteristics that give us an advantage as a species will survive.  Our ancestors lived in harsh environments where food was not always readily available or varied.  We evolved to be omnivores which mean we eat a varied diet of fruit, veg, leaves and meat.  In the past it would be a challenge to avoid malnutrition and eat enough to be able to be physically active.  

• Sweet, salty and fatty foods are particularly valued in an environment where food supply is scarce or erratic as they have vital requirements and were relatively rare for our ancestors.  
• At that time it was advantageous to overeat in times of plenty as it would make your survival chances better, i.e. this is adaptive behaviour.  
• In an evolutionary sense we are also programmed to use little energy, to conserve our calories.
• Nowadays this is not needed as a survival strategy but people find it hard to escape these evolutionary pressures.  So now we eat more than we should but do not use up the same energy in our day to day living.  
• We are naturally impulsive eaters.  These behaviours in our obesogenic environment (this means that in our modern world there are weight problems because of the easy availability of fast-food, and other factors that encourage an unhealthy lifestyle, e.g. cars) are no longer adaptive.

Preference for high-fat foods

• Fat contains twice as many calories as the same amount of protein or carbohydrate. 
• It was not easily available to our ancestors so when it was found it was sensible to binge on it
• Now these foods are readily available and people find it difficult to keep fat consumption low

Preference 

• Sweet taste is associated with ripeness and a high intake of sugar is a quick fix of calories. 
• Desor et al showed that babies have a preference for sweet tastes over bitter tastes (this is probably safer though). 
• How a preference for sweet things may not encourage us to eat berries, etc, but to eat high-calorie, energy-dense foods such as chocolate

Preference for salty foods

• Salt is essential for a body to function and we need to keep the level constant. 
• Now we have easy access to it, but it is not easy to get in the wild. 
• Consuming too much can cause serious problems. Children show a preference for it after 4 months of age.
• This preference may make us want to eat high-fat foods flavoured with salt, e.g. chips.

Food neophobia:

• Avoidance of certain unfamiliar foods.  
• It helps us to avoid dangerous foods.
• This can mean we/animals have a dull diet, but it is safe.  
• As we become more familiar with things we develop more of a preference and less of a fear.- Helps to keep us alive

Taste aversion:

• If we eat a food that is new and it makes us sick it would make sense that we should not eat that food again.  It is highly specific and very intense,
• Garcia et al (1977) made wolves sick with poisoned lamb’s meat.  When allowed to approach live sheep, the wolves would leave them alone once they had sniffed them.  They had learned to associate sheep with poison (sickness).

Embryo protection hypothesis

• During early pregnancy women often experience changes in their food preferences.  They often want to avoid certain foods due to disgust and vomiting.  ‘Morning sickness’ is found in 75% of women.  The most avoided foods are meat, alcohol, eggs, coffee, tea and vegetables.  (Partly on advice from Drs).
• During the first few weeks of pregnancy the developing foetus and its organs is most vulnerable so it makes sense that morning sickness is at its worst then.  Meat and eggs are common sources of toxins such as bacteria that could be harmful to a foetus.  Caffeine is also problematic.
• The vomiting reduces the risk of toxins entering the bloodstream and the feeling sick helps avoid dangerous foods.  However nowadays food hygiene is much better so ‘morning sickness’ is an evolutionary hangover

Self control and metabolic rate

• If evolutionary theory is correct then animals should be more impulsive when eating and be less willing to delay for a larger amount of food later over a smaller amount immediately. 
• Animals that have higher metabolic rates (who have greater cost when not eating) show less self-control for food 
• Tobin & Logue (1994) found that pigeons (very high metabolic rate) are more impulsive than rats and humans who have lower metabolic rates. In general this is found across the animal kingdom. 
• One exception is the macaque monkey who has a high metabolic rate but enormous self-control. It’s thought this is because they lie in an environment that has abundant food, all year round.

Strengths

• Can explain innate food preference
• Can explain surge of obesity 

Weaknesses

• Reductionist - It may be regarded as an over simplification of a very complex behaviour. In fact, there are many influences on our food choices e.g. emotions, social factors, etc. 
• Deterministic – suggests that when we come across certain types of food we have an instinctual urge to eat it, ignores free will
• Difficult to falsify; Cannot prove or disprove it in a scientific way
• Focus on nature and not on environment