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(A2) Eating Behaviour
Transcript of (A2) Eating Behaviour
Neural mechanisms in eating and satiation:
Explanations for the success and failure of dieting:
1) The restraint theory
2) The role of denial
3) Attention to detail - the key to a successful diet
1) Early diets
2) Preference for meat
3) Taste aversion
1) Social learning theory
2) Cultural influences
3) Mood and eating behaviour
- One way children acquire eating behaviour and attitudes to food is by observing the behaviour of their parents.
- Parents affect attitudes to food as they control the food they bring in the house and the meals they provide at home.
- Brown et al reported consistent correlations between parents and their children in terms of snack food intake, eating motivations and body dissatisfaction.
- Role of social learning is evident in the impact of television and other media such as magazines on attitudes to eating.
- MacIntyre et al found that the media has a major impact both on what people eat, and also their attitudes to certain foods.
- However, these researchers also state that many eating behaviours are limited by personal circumstances.
-Thus, people appear to learn from the media about healthy eating.
Evaluation of SLT
Meyer and Gast demonstrated the importance of SL in attitudes to food. They did this by surveying 10-12 year old girls and boys and found that there was a positive correlation between peer influence and disordered eating.
SL is also supported through a study of mothers and daughters by Birch and Fisher. They found that the best predictors of daughters' eating behaviour were the mothers dietry restraint and perception of their daughters becoming overweight.
Much more than learning?
Attitudes to food are clearly more than SL alone. For example evolutionary explanations show how our preference for fatty and sweet foods is a direct result of an evolved adaptation among our distant ancestors over two million years ago. E.g. Hadza tribe
- Powell and Khan found that body dissatisfaction and related eating disorders are more common in white women than black and asian women.
- However, Ball and Kenardy studies over 14,000 women between the ages of 18 and 23 in Australia. Results showed that for all ethnic groups, the longer the time spent in Australia, the more the women reported attitudes and eating behaviours similar to women born in Australia - the acculturation effect.
- A number of studies have found that body dissatisfaction, dieting behaviour and eating disorders are more common in higher-class individuals.
- Dornbusch et al surveyed 7,000 American adolescents, and concluded that the higher-class females have a greater desire to be thin, and were more likely to diet to achieve this, than their lower-class counterparts were.
- Goode et al used data from the 2008 Scottish Health Survey and established that income was positively associated with healthy eating.
Evaluation of cultural influences:
- Mumford et al found that the incidence of bulimia was greater among Asian schoolgirls than among their white counterparts.
- Similarly, Striegel-Moore et al found there were more evidence of a 'drive for thinness' among black girls than among white girls.
- In direct contrast to Dornbusch et al's study, Story et al found that in a sample of American students, higher social class was related to greater satisfaction with weight and lower rates of weight control behaviours such as vomiting.
- Other studies have found no relationship between social class and weight dissatisfaction, the desire for thinness and eating disorders.
Mood and eating behaviour:
- Research shows that people who binge complain of feeling anxious prior to a binge.
- Davis showed that one hour before a binge, individuals have more negative moods than one hour before a normal snack or meal.
- This can be seen in sub-clinical populations.
- Garg et al showed participants either a funny or sad film; offering them either popcorn or grapes to eat.
- They found that those watching the sad film consumed 38% more popcorn than those watching the funny film eating more grapes.
- Suggests people who eat food that tastes good when they feel sad as it gives them a rush of euphoria. Happy people want to stay happy so go for the healthy option.
- However, when a nutritional advert was shown before film, popcorn consumption dropped in both conditions.
Evaluation of mood and eating behaviours:
- Studies suggest that the lower mood prior to binge eating causes the onset of the binge eating. Although the binging offered instant gratification, it is short lived and studies report a drop in mood immediately after the binge. Thus questioning why people binge as a mood reinforcement.
- Chocolate is reported to lift our mood. However, Parker found that although chocolate has a mild antidepressant effect for some, it is more likely to prolong rather than alleviate the negative mood particularly if used repeatedly as a mood lifter.
- The studies come from a variety of groups, some clinical and some sub-clinical, and others represent the non-clinical population. This puts limitations on the degree to which we can generalise from one group to another, and therefore the degree to which these studies offer a universal understanding of causal factors in eating behaviour.
1) Homeostasis (LH and VMH)
2) Neural control of cognitive factors (the amygdala and the inferior-frontal cortex)
- Involves mechanisms which both signal the need for nutrients and correct the situation to its normal state.
- However, there is a time delay so by the time enough food has been eaten to restore levels, only a small amount has been digested so the receptors detecting the levels have insufficient data to turn off eating.
- Two systems:
1) Glucose plays an important role in feelings of hunger, hunger increases as glucose levels drop. This activates the lateral hypothalamus resulting in feelings of hunger (turns eating on).
2) Once eating, glucose levels rise again. This activates the ventromedial hypothalamus leading to a feeling of satiation, thus inhibiting further eating (turns eating off).
- Zhang et al found that research with mice who recieved 2 copies of the ob/ob gene for obesity had a tendency to overeat, and had a defective gene which produced leptin (protein causing fat loss). Once injected leptin, mice lost weight. GOOD AS IT IS SCIENTIFIC ALLOWING CAUSE AND EFFECT TO BE MEASURED (VALID)
- For a hunger mechanism to be adaptive it must both anticipate and prevent energy deficits - not just react to them. This suggests that the mechanism only kicks in once the nutrient levels are low is not realistic. To be adaptive it should keep levels above the optimum to act as a buffer in case a lack of availability to food.
Basically: if food isn't enough and glucose levels have dropped for the LH to become activated it might take a while to find food, so homeostasis is false to this theory.
Research from damaged LH leading to aphagia (not eating at all) and stimulation to the LH has led us to believe the LH is the on-switch for eating behaviour.
- Recent research shows eating behaviour is controlled by neural circuits throughout the brain, not just the hypothalamus.
- Although important, it is not the brain's eating centre as once thought - Sakarai stated.
- A neurotrasmitter in LH called NPY (neuropeptide Y) is important to the on-switch of eating.
- When injected in the hypothalamus of rats they immediately start eating, even when full (Wickens)
- Repeated injections cause obesity in rats after just a few days.
- Marie manipulated mice so they couldn't produce NPY and found there was no decrease in eating behaviour which suggests that the injections in the previous study caused an artificial reaction.
- RLA: Research shows that NPY in the LH has an important role on eating behaviour. Suggests a cause of obesity is the brain producing NPY in excessive amounts so always feeling hungry. However, NPY is also produced by abdominal fat.
- Yang et al believes that to treat this, patients need injections of drugs inhibiting NPY production, hopefully preventing obesity.
- Damage to the VMH leads rats to overeat leading to the condition hyperphagia (eating lots).
- Research shows that the VMH is the off-switch for eating signalling to stop.
- However, the paraventricular nucelus (PVN) - part of the hypothalamus seems to be responsible for detecting specific foods our body needs and for our food cravings.
- Previous research in animals and humans led researchers to designate the VMH as the 'satiety centre' in eating behaviour.
- Gold showed that lesions specifially leading to the VMH did not result in hyperphagia (against)
- However, recent research concludes the original theory showing animals with damaged VMH eat more and gained weighht.
Neural control of cognitive factors:
This explanation states that we often become hungry when thinking about food; when we see or when we smell food. Neural control for these cognitive factors in hunger lie in 2 main brain areas:
1) The Amygdala:
- The role of the amygdala is primarily in the selection of foods on the basis of previous experience.
- Rolls and Rolls found that surgically removing the amygdala in rats would cause the animals to consume both family and novel (unfamiliar) foods, whereas 'normal rats' who had their amygdala intact were found to avoid novel foods and consume familiar foods instead.
2) The inferior frontal cortex:
- The role of the inferior frontal cortex is to recieve messages from the olfactory bulb (responsible for smell)
- Kolb and Whishaw stated that because odours influence the taste of food, damage to this area decreases eating.
Evaluation of neural control:
- Damage to the amygdala and inferior prefrontal cortex could explain the feeding abnormalities observed in Kluver-Bucy syndrome.
- Patients with this syndrome typically showed an increased appetite, indiscriminate eating, and even attempts to eat non-food items.
- Research shows damage causes food cues to no longer be accurate in representing their real reward value to the individual.
- Zald and Pardo supported the claim that the amygdala participates in the emotional process of the olfactory stimuli.
- They exposed healthy adult participants to aversive olfactory stimuli whilst measuring blood flow to the amygdala by means of a PET scan.
- These produced increased blood flow to the amygdala, whereas non-aversive stimuli did not.
Evolutionary explanations for food preference:
To understand the adaptive problems faced by our distant ancestors, we must understand the environment in which they lived. The EEA refers to the environment in which a species once evolved.
- Early humans were hunter-gatherers whose diet included the animals and plants that were part of their natural environment.
- Preferences for fatt food would have been adaptive for early humans, because conditions in the environment of evolutionary adaptation (EEA) meant that energy resources were vital in order to stay alive and find the next meal.
- Modern humans are more concerned with the nutritional value of food but what we actually eat is oftten high in calories and low in nutritional value.
- In the EEA, calories were not as plentiful as they ar today so it follows that we have evolved a preference for foods that are rich in calories.
Evaluation of early diets:
- This can be done through comparison with different species.
- We can study a related species - for example a chimp for faced similar adaptive problems today to the one who faced in the EEA.
- Importance of calories in early diets: Gibson and Wardle provided evidence to support the importance of calories in an ancestral diet. They showed that children's choice of fruit and vegetables was determined by how dense they were in calories. Bananas and potatoes particularly calorie reach were the most likely to be chosen. So - this supports the theory that we have evolved a preference for calorie rich food (absence of meat = go for more calorie rich food)
Preference for meat:
- Fossil evidence shows that hunter-gatherer daily diet consisted of mainly meat; especially animal organs such as the liver, kidneys and the brain which are rich in energy.
- A meat diet, full of densely packed nutrients, privded the catalyst for growth of the brain.
- Milton suggested that if we had relied on vegetables for energy we would never have evolved.
- Meat supplied early humans with essential amino acids, minerals and nutrients that they required which allows them to supplement their diet with low-quality plant based foods, with few nutrients but lots of calories.
Evaluation for preference for meat:
- Evidence from other primates suggest our ancestors meat was an important source of saturated fat; fat was vital for survival but not always readily available. Stanford showed that if chimpanzees are close to starvation when they kill an animal they go straight for the fattiest parts (brain and bone marrow) rather than the tender flesh.
However, we are not 100% linked with chimps (generalisability problem)
- Cordain argued that early humans got most of their calories from sources other than animal fat.
- Anthropological evidence from Abrams showed all societies display a preference for animal foods and fat. Early humans would not have been able to get sufficient calories from the plants and grains available.
- Many of the foods important to our ancestors are harmful in modern environments so we are more likely to avoid them in order to remain healthy.
- First discovered by farmers trying to rid themselves of rats. They found it was difficult to kill rats with poisioned bait because rats would only take a small amount of unfamilar food, and if they became ill, would rapidly learn to avoid it.
- Garcia et al tested taste aversion within the lab. Rats who had been made ill through radiation shortly after eating saccharin, developed an aversion to it and very quickly associated their illness with saccharin.
- Not only the tase but the odour of the food can belinked to illness and lead to food aversion.
- The development of taste aversion would have helped our ancestors to survive as they would learn not to eat poisoned food again if they survived it.
- A taste aversion can still be acquired up to 24hrs after consumption of food as the reaction to poisoned food in natural environment which can be delayed. Once learnt, aversions are difficult to shift.
The medicine effect:
- There is also evidence that animals can learn a preference that makes them healthier, with any food eaten just before recovery from illness being preferred in the future.
- Garcia also found that when a distinctive flavour is given to a thiamine deficient rat and then followed by a dose of thiamine, the animal will acquire a preference for that flavour.
Evaluation of taste aversion:
- Seligman claimed diffrent species evolved different learning abilities, known as biological preparedness. This occured so each species has the ability to learn certain associations that help them survive better than others.
- RLA: Research on taste aversion helps to understand the food avoidance that occurs in cancer treatement. When food is coupled with the effects of radiation, aversion can occur.
- Berstein and Webster gave cancer patients a novel tasting ice-cream prior to chemotherapy and they acquired an aversion to it. These findings have led to the developmet of the 'scapegoat technique'; if given a novel and familar food prior to treatment, the patient will only form an aversion to the novel food. This being consistent with an adaptive avoidance of novel foods (also known as neophobia)
- Fatty and sweet foods seem to be universal. Innate responses don't account for likes and dislikes. Cultural differences do exist, but are a fine tuning of evolved preferences for meat.
- Bitter taste evolved as a defence mechanism to detect harmful toxins in the environment. Sandell and Breslin found those with the sensitive gene rated the glucosiolate containing vegetables as 60% more bitter than those with the insensitive form of the gene.
- Research suggests that up to 98% of the UK female population consciously restrain their food intake at some point in their lives.
- Herman and Mack developed the restraint theory to explain both the causes and consequences of the cognitive restriction of food intake. This suggests that attempting not to eat actually increases the probability of overeating.
- Wardle and Beales carried out a study to test this prediction. It concludes that overeating of many dieters is actually caused by their attempts to diet. They assigned 27 obese women over seven weeks to either a control, diet or exercise group. They found that women in the diet groups ate more than those in the other two groups.
- The boundary model also fits into this explanation. Herman and Polivy states that hunger keeps intake of food above a certain maximum, and satiety works to keep intake below a certain maximum (we eat when we are hungry, stop once full). Psychological factors have greatest impact on consumption, and dieters tend to have a large range between the two levels; tend to get hungry quicker and need more food to satisfy them.
- This theory suggests restraint leads to excess, yet obesity treatment often recommends restraint.
- Failure in diets can lead to depression and an inability to control weight
- Ogden stated that obesity may not lead/ be caused by overeating, overeating may be a consequence of obesity if restraint is used as a treatment.
- Restraint theory suggests an association between food restriction and over-
eating. However, Ogden questions if trying not to eat results in over-
eating, how do anorexics manage to starve themselves?
The role of denial:
- Research in cognitive psychology has shown that attempting to suppress or deny a thought frequently has the opposite effect, making it even more prominent.
- Wegner et al demonstrated this by asking participants not to think about a white bear, but to ring a bell if they did, and others to think about the bear.
- Results from this study showed that those told not to think about the bear rang their bells far more often than participants instructed to think about the bear.
- Wegner refers to this as the 'theory of ironic processes of mental control' as it represents a paradoxial effect of thought control (denial often backfires).
- Soetens divided participants into restrained eaters and unrestrained dieters. He found that restrained group used more suppression than the other group which led to even more thoughts about food, and more eating.
- However, Wegner admitted that these 'ironic effects' are quite small. If these do underlie some form of overeating, their influence may be huge in terms of health.
- Think about the mundane realism of the task.
Attention to detail - the key to a successful diet.
- Recent research by Redden suggests that the secret of successful dieting lies in the attention we pay to what is being eaten.
- He claims that people usually like experiences less as they repeat them.
- When it comes to dieting, this makes it significantly harder to stick ot a regime.
- To overcome this, suggested Redden, instead of thinking 'not another salad' we should focus on the details of the meal. By doing this, people will eventually get bored less easily and are better able to maintain their food. (more variety on plate will result in boredom, and end up in not managing to finish the food).
- Redden's jellybean expriment: gave 135 participants 22 jelly beans each, one at a time. As each was dispensed, information appeared on the screen either general or specific information. He found that group one got bored quicker than group two.
- There are also concerns with the ineffectiveness of dieting which has led to programmes aimed at replacing diets with conventional healthy eating. These emphasise regulation by hunger and satiety signals and prevention from inappropriate attitudes to food.
- Higgins and Gray found participation in these programmes was associated with improvements in eating behaviour and psychological well-being and with weight stability.
- This is a cogntive explanation focusing on thought processes and our minds, therefore ignoring the role of biology and genetics; e.g. VMH and LH
- Lacks mundane realism (experiment)
- Research by Mckenna shows how paying less attention to what you're
eating can lead to individuals becoming bored easier and eating
- Ignores body signals - not just down to detail, could
links to olfactory bulb (prefrontal cortex).
Some cultural groups find it harder to diet successfully because of a natural inclination to obesity - Asian adults more than Europeans.
Genetics can exert an influence on our weight. LPL enzyme produced by fat cells to store calories as fat. If too much is produced, the body will be effieient in storing calries away.