Eating behaviour essays

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  • Created on: 08-06-15 12:27

Neural mechanisms

AO1

  • The hypothalamus is situated in the brain and helps to regulate the body’s internal environment.
  • The dual-centre theory of feeding behaviour is based on two areas of the hypothalamus.
  • The lateral hypothalamus (LH) contains the feeding centre and initiates eating.
  • It responds to decreased blood glucose and increases in ghrelin, a hormone released from the stomach when it is empty.
  • The Ventro Medial hypothalamus (VMH) contains the satiety centre, which inhibits eating behaviour when we are full.
  • The VMH responds to an increase in blood glucose and a decrease in ghrelin as well as to the release of CCK, a hormone released when food is detected in the duodenum.
  • It also responds to leptin, a long-term satiety signal released by fat cells.

 

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Neural mechanisms

  • Hetherington and Ranson (support for hypothalamus) - made lesions on area of VMH in rats
  •  -> this lesion destroyed a centre that is vital for the control of feeding behaviour.
  • Its destruction led to an increase in and body weight. It was assumed that this was a satiety centre, which is normally activated when the animal is full at the end of the meal.
  • Anand and Brobeck - a lesion in the LH led to a loss of feeding behaviour known as aphagia.
  • Further studies also confirmed the role of the hypothalamus in feeding behaviour showing that when electrically stimulated the VMH inhibited feeding behaviour whilst stimulation of the LH produced normal feeding.
  • -> researchers concluded that VMH signals ‘stop eating’ as a result of the many glucose receptors in the area & the stimulation of the LH was the ‘on switch’ for eating behaviour.
  • Strength -> lab based -> all variables are easily controlled and the study can be repeated to increases its reliability.
  • Weakness -> may lack external validity as people may behave differently outside of the controlled environment.
  • Non-human animals -> raises the problem of generalising the results from animals to humans, as it cannot be assumed that humans will react in the same way to non-human animals.
  • Ethical issues concerning the use of non-human animals eg animal rights and welfare. 
  • Approval must be gained from ethic committees and a government license needs to be obtained in order to overcome this.

 

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Neural mechanisms

Ghrelin

  • Empty stomach sends signals to the brain to start eating. Although these signals may include direct neural pathways from the stomach to the brain, an important role is played by the hormone ghrelin.
  • Ghrelin is secreted from the stomach and the quantity of the hormone that is produced is directly related to the emptiness of the stomach, i.e. as the time from the last meal increases and we feel hungrier, so ghrelin secretion is increased.
  • Cummings et al investigated changes in blood ghrelin levels over time between meals.
  • 6 participants were allowed to eat lunch, and then ghrelin levels were monitored from blood samples taken every five minutes until the participants requested their evening meal.
  • Participants assessed their degree of hunger every 30 minutes.
  • They found that ghrelin levels fell immediately after eating lunch, reaching their lowest level at about 70 minutes.
  • Then they slowly began to rise, peaking as participants requested their evening meal.
  • Importantly, in 5 out of the 6 participants ghrelin levels were closely correlated with the degree of hunger reported by the participants -> supports a role for ghrelin as a key appetite signal in humans.
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Neural mechanisms

AO2 - Cummings et al.

  • Strength -> participants were isolated from time and context cues so that any changes in ghrelin levels would be due to hunger rather than reflecting an automatic response to signals that mealtime was approaching.
  • Problems -> data was correlational, so we cannot say that ghrelin causes feelings of hunger, as there are many other factors that need to be considered.
  • -> only 6 participants, very small sample -> due to the small number of participants we cannot assume that all individuals within the population will behave in the same way.
  • -> all participants were male, meaning that the study can be criticised for gender bias. As a result of this it is difficult to generalise the findings of the study with accuracy to the wider population in general and to females in particular.
  • Ethical issues -> study involved inserting a catheter into the participant’s vein so that blood samples could be collected. The researchers obtained approval for this from their local ethical committee. Participants also gave informed consent and were fully debriefed following the study.
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Neural mechanisms

AO3

Although food choice may relate to neurochemicals and brain pathways, eating is an inherently social behaviour and often takes place in the presence of others. Food therefore represents a range of important social meanings. Our biological drives are often moderated and modified by social drives. A biological approach assumes that an individual will respond to hunger by eating. However, many individuals override their physiological drive to eat due to factors such as a desire to lose weight or a dislike of food. 

  • Reductionist – focus exclusively on biological apsects of hunger and satiety
  • Biological determinism – focus exclusively on the role of nature and no space left to choice and cultural and social influences
  • There is substantial and convincing evidence that social, cultural and psychological factors affect our eating behaviours as is evident from psychological explanations of eating disorders.

 

 

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Success and Failure of dieting

Herman and Polivy -> the boundary model as an explanation for the failure of dieting.

  • The boundary model suggests that restrained eaters, i.e. dieters, create a psychological boundary for themselves, which is a significant distance away from their biological boundary.
  • Whilst sticking to the psychological boundary would result in weight loss, the boundary model claims that dieters are highly likely to eat past this boundary with the inevitable outcome of overeating all the way up to, and potentially past, their body’s biological boundary.
  • This would result in weight gain and complete failure of the diet, particularly if the pattern were to be repeated over several days or weeks. In order to be able to succeed at dieting, the model suggests that the psychological and biological boundaries should be set close to on another, thus reducing the chance of over eating and dieting failure.
  • If this were the case, the dieter would be less likely to overstep their psychological boundary due to hunger or over-eating, and the diet would be successful.
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Success and Failure of dieting

Herman and Mack (support of the boundary model)

  • They found that unrestrained eaters eat less ice cream in the two milkshake preload condition than in the one or no preload condition.
  • This was predicted, as they should feel fuller after two preloads than after one or zero preloads.
  • Unrestrained eaters follow their biological set point, and eat less after preloads as they are already close to their set point.
  • However, the restrained eaters (dieters) showed a different pattern.
  • They ate more ice cream after one or two milkshake preloads than after zero preloads.
  • This is because restrained eaters have a cognitive boundary as well.
  • With no preload, they eat ice cream until they reach this boundary.
  • However, in the high-calorie preload conditions, the preloads push them beyond this cognitive boundary.
  • They then have a ‘what the hell effect’ and eat until they reach their biological set point i.e. more than in the no preload condition.
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Success and Failure of dieting

AO2 - Herman and Mack (evaluation)

  • Weakness -> Individual differences have not been accounted for. It cannot be assumed that everyone will like ice cream to the same level.
  • Criticism -> small sample size. This means that due to a small number of participants we cannot assume that all individuals within the population will behave in the same way. As a result it is difficult t generalise the findings of the study with accuracy.
  • Criticism -> age biased. This means that all participants are from the same age group. Therefore it cannot be assumed that all individuals within all age groups will behave in the same way. As a result the findings cannot be generalised with accuracy.
  • Other weaknesses -> gender bias/social bias. These factors make it difficult to generalise the findings, as we cannot assume that all individuals will behave in the same way.
  • The participants were also deceived in this study. They believed to be taking part in a ‘taste test’ but actually they were assessed on how much they consumed.
  • A debrief would be required at the end of the study, informing the participants on the full details of the study and offering any form of counselling if needed.

 

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Success and Failure of dieting

Over-eating is another reason as to why diets fail.

  • There is evidence to suggest that there is a causal link between dieting and binge eating.
  • The theory is that attempting not to eat will cause you to over eat.
  • Wardle and Beale support this theory.
  • -> conducted a lab based study assessing food intake at 4 and 6 weeks.
  • 27 obese women were randomly assigned to experimental group, exercise group and control group.
  • They found that participants in the diet group ate more than the exercise and control group. These findings support the causal link between dieting and over eating as participants in the diet group ate the most. One strength of this study was that it was lab based. This meant that manipulation of variables could take place and be controlled, leading to increased reliability. The participants were randomly allocated to the different groups, which remove any problems associated with bias. Also, participants were from a non-student sample, which means there is no age bias and results may be more generalisable.
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Success and Failure of dieting

Another explanation for the failure of dieting is the role of denial, which suggests that attempting to suppress thoughts of foods is counterproductive and has the opposite effect.

Wegner (1987

  • Pps were asked to try not to think about a white bear but to ring a bell if they did. The results showed that those trying not to think about the bear actually thought more frequently about the bear than those who were told to think about the bear. 
  • Therefore as soon as a food is denied, it becomes more attractive and likely to be eaten which ruins the diet.
  • Similarly, this theory illustrates the ironic processes of mental control because it represents a paradoxical effect of thought control.
  • Diets often fail because when a restricted food becomes forbidden, the denied food becomes more attractive making attempts to suppress it difficult.
  • Soetens (support for role of denial)
  • found that restrained eaters (those who try to eat less but often eat more) used more thought suppression than other groups.  Thus restrained eaters try to suppress food thoughts more often but end up thinking more about the food and therefore wanting it.
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Factors influencing attitudes to food

The social learning theory emphasises the impact that observing other people has on our own attitudes/behaviour towards food. Our eating behaviours are a result of observing models actions. Parental modelling -> a child’s eating behaviour is learnt by observing the behaviour of their parents. Parents have a control of the foods brought into the house - control what is being eaten.

  • Brown and Ogden (2004) support the involvement of parents
  • They reported a consistent correlation between parents and children in terms of their snack food intake, eating motivations and body dissatisfaction.
  • Criticism -> based on a correlation and therefore we cannot determine a cause and effect of the results, meaning that we cannot determine which variable causes the change in the other variable.
  • Olivera et al also offers support for social learning as a way of developing attitude to food.
  • -> conducted a study into the relationship between a parent and a child’s eating behaviour.
  • -> reported a clear relationship between a mother’s food nutrient intake and that of her pre-school children and suggested that parents could be targeted to help combat -ve eating habits.
  • This research suggests that parents eating habits are highly influential over their child as children view their parents as models and imitate the perceived behaviour.
  • Criticism -> reductionist -> theory suggests that the only answer to our eating behaviour is our social ability -> Therefore overlooks other approaches such as the cognitive and biological -> Our thought processes might have an effect on the way we eat 

 

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Factors influencing attitudes to food

AO1 - Mood

  • Our mood is known to influence what and how much we eat.
  • People eat in response to their mood regardless of their weight.
  • Gibson (2006) heavily criticises research assuming eating habits are learnt from parents
  • Gibson gives a much more biological approach for eating behaviours with scientific and empirical basis.
  • He argues that when individuals are stressed out, they tend to eat more carbohydrates (especially chocolate).
  • This is because carbohydrates such as chocolate contain the amino acid tryptophan.
  • This is used by the brain in the manufacture of serotonin. Low levels of serotonin are associated with depression, and it has been proposed that people with stress or depression take in more carbohydrates because it leads to increased levels of serotonin in the brain.
  • This effectively reduces their depression.
  • However, such biological explanations tend to eliminate all aspects of free will and assume that eating habits are determined with no human control. (deterministic)

 

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Factors influencing attitudes to food

  • Cultural influences eg ethnicity can affect eating behaviours as ethnicity can influence attitudes towards food preferences -> due to availability of food, location and how we have adapted to eating within certain cultures or how individuals learn from others such as role models and exposure to different food types.
  • Leshem (2007) -> studied Bedouin Arabs in a desert and urban area.
  • He compared these results to Jewish women -> found that the diets of the different Bedouin women were hardly any different whether they lived in a desert or urban area and that both groups diet was significantly different from the Jewish women.
  • The Bedouin women also had significantly higher salt intake, probably related to the high fluid and salt loss associated with living in the desert.
  • The findings show that cultural influences on diet are profound and persist even when there is equal access to the same foods.
  • These differences may originate in adaptations to previous environments or strict religious backgrounds dictate what can be eaten and what cannot.
  • Strength -> very high ecological validity as it was a natural experiment
  • Weakness -> fails to account for male Bedouins or other ethnic groups outside of the Jewish or Bedouin community and therefore the results cannot be generalised to the wider population.
  • Diet can show clear cultural variations, however, we cannot conclude that these are environmental (nurture) effects rather than inherited tendencies (nature). 
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Factors influencing attitudes to food

Wardle et al -> proposed further evidence for cultural differences in eating behaviours.

  • Studied 16,000 participants in 23 countries
  • He found that Portugal, Italy and Spain eat less fibre and more fruits (probably due to availability). Norway and Denmark eat more fibre probably due to the cold climate. England and Scotland eat less fruit due to availability and importation uncertainties.
  • Criticism -> fails to acknowledge difference in non-western countries -> we cannot apply these findings to continents such as Africa.
  • Eating habits can sometimes be due to the amount of activity that individuals partake it. Eg in Mediterranean countries the food intake is high but because people move around more and are relatively more active it means that their weight stays constant despite excess consumption.

 

 

 

 

 

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Biological explanations of AN

It is accepted that there is a genetic component to eating disorders such as anorexia.

  • Family studies have shown that first-degree relatives of AN have an increased risk of developing an eating disorder.
  • MZ twins are genetically identical. If a characteristic is entirely determined by genetics, then both twins must have it.
  • DZ twins are genetically similar like brother or sister -> share the same environment, so they act as a control for the fact that MZ twins share the same environment.
  • In theory, the only difference between MZ and DZ twins is the fact that MZ twins have the same genes.
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Biological explanations of AN

AO2 - Genetics

  • Holland et al. conducted a longitudinal study in support of the role of genetics.
  • In this study a sample of 16 MZ female twin pairs were compared with 14 DZ female twin pairs. One of the pairs had already been diagnosed with AN.
  • MZ or DZ was determined for most via blood group analysis.
  • The remainder was determined using a physical similarity questionnaire.
  • It was found that the concordance rate in MZ twins was 55%, whereas the concordance rate for DZ twins was 7%.
  • As the concordance rate was significantly greater in MZ twins than DZ twins (the only difference between the 2 was genetic make-up) this suggests a significant genetic involvement in AN, therefore supporting the theory.
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Biological explanations of AN

AO2 - Holland et al. (evaluation)

  • Strength -> longitudinal -> twins were studied over a prolonged period of time -> findings therefore have increased levels of reliability and validity.
  • Criticism -> concordance rates amongst the twins were not 100%, which is an indication that genetics is not the only factor that contributes towards the development of AN.
  • Criticism -> study does not take into account any other possible factors that may make an individual more susceptible to anorexia eg environmental influences -> can only be studied if psychologists were able to examine a sample of MZ twins who had been reared apart, however, this wasn’t possible in Holland’s study.
  • Criticism -> lacks population validity -> only a very small sample of twins was studied -> sample also consisted of entirely females, therefore making it gender biased. Both these factors mean that the findings cannot be generalised across the population with confidence.
  • Strength -> Blood group analysis -> reliable scientific way of distinguishing between MZ/DZ
  • Criticism -> using a questionnaire is subjective and therefore can be deemed unreliable.
  • It was assumed the environment was the same for both MZ/DZ twins.MZ twins are often treated differently to DZ twins ie dressed the same way -> extra closeness could affect conc. rates.
  • Ethical issues -> Studies using participants with psychological disorders such as AN must be carefully vetted for fully informed consent and the right to withdraw at any time. Professional help, eg counsellor, should be available if necessary.
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Biological explanations of AN

The role of serotonin in controlling eating behaviour is that serotonin acts as an appetite suppressant. There is considerable evidence available which suggest that increased levels of serotonin in the brain causes appetite suppression and may be responsible for the onset of behaviours which are characteristic of anorexia nervosa.

Kaye et al (supports role of serotonin in AN.

  • Using PET scans, Kaye et al found that individuals with eating disorders ie AN had a lower level of a serotonin metabolite and fewer serotonin receptors in the brain.
  • This research supports the idea that a serotonin imbalance contributes to the onset of AN, as the findings show that there is an abnormality in the serotonin pathways of anorexics.
  • Strength -> scientific method of measuring -> objective and thus increases reliability.
  • Criticism -> the suggested link between serotonin levels and AN is only correlational. It would be almost impossible to prove whether the increased levels of serotonin are responsible for AN, or simply, occur as a result of AN.
  • The only way that an accurate conclusion could be drawn would be if serotonin levels could be monitored before an individual developed AN -> this would be extremely problematic, which is a criticism because the theory that a serotonin imbalance can be linked to the onset of AN therefore lacks validity.
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Biological explanations of AN

AO3

Reductionist -> biological explanations do not take into account any other factors aside from biology which may contribute towards the development of AN.

Deterministic -> the explantions imply that AN is caused purely by biological factors and ignore the concept of free will.

 

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