Transcript Eating Behaviour - Beauchamp College

Eating Behaviour
Unit PSYA3
Miss Bird
What will we cover in this topic?
Factors influencing attitudes to food and eating behaviour. For example:
Eating behaviour cultural influences; psychological influences (mood); and social influences
(health concerns/media).
Explanations for the success and failure of dieting.
Neural mechanisms involved in controlling eating behaviour.
Biological
explanations of Evolutionary explanations of food preference.
eating behaviour
In relation to either anorexia nervosa or bulimia nervosa:
Eating disorders
Psychological explanations.
Biological explanations, including neural and evolutionary explanations.
What we have covered
Where we are now
Evolutionary explanations
of food preference
The goal of any evolutionary explanation is to discover the
adaptive function of a particular behaviour i.e. what is the purpose
of that particular behaviour?
The mechanisms that make up human nature were designed by
natural selection millions of years ago.
Therefore we need to consider the problems faced by our distant
ancestors to discover why behaviours, such as food preferences,
evolved in the first place.
Darwin: Natural selection
Individuals will behave in such a way as to maximize their
survival and their reproductive potential.
Individuals that survive maturity are more likely to produce
offspring and be able to ensure the long-term survival of their
young.
Therefore, in terms of evolutionary theory, it pays to be healthy in
terms of what we eat in order to survive and pass on our genes to
our offspring.
The evolution of food
preferences
The environment of evolutionary adaptation (EEA)
 Early diets were dependent on the environment that
humans found themselves in.
 Preferences for fatty/high calorie food would have been
adaptive for early humans as a source of energy.
 Conditions in the EEA at this time meant that energy
resources were not only vital to stay alive but were
needed to provide the human with enough energy to find
their next meal.
Continued…
 Unlikely that humans would get enough
nutrients from a vegetative diet alone.
 Therefore began to include meat in their
diets.
 Evidence from fossils suggests that their
daily diet consisted primarily of animalbased foods, in particular organs, which
are a rich source of energy.
Continued…
 A meat diet full of densely packed nutrients
provided the catalyst for the growth of the
brain.
 Meat supplied early humans with all the
essential amino acids, minerals and nutrients
they required, allowing them to supplement
their diet with plant-based food that have few
nutrients but lots of calories for energy (e.g.
wheat).
To summarise…
Our modern preferences for calorie-rich/fatty food
can therefore be traced back to the adaptive
problems faced by our ancestors.
I.e. we prefer foods that are high in calories so that
we can supply our brains and bodies with the
energy that we need to survive and reproduce.
Independent task
Read the study by Gibson and Wardle (2001) and
answer the questions in your booklet.
You have 10 minutes.
What do we like (and not
like)?
Who can identify some different tastes?
1. Sweet – identify foods rich in carbs to provide us with
energy.
2. Sour – associated with food that has gone off and therefore
should be avoided.
3. Salt – critical for functioning of the cells and therefore need
to identify.
4. Bitter – associated with poisonous plants, should be
avoided.
Are we predisposed to food preferences?
• There is evidence that we are born with genetic
predispositions for basic tastes and that these
influence our food preferences.
• One suggestion is that we are predisposed to
prefer sweet and salty foods and to reject bitter
and sour foods.
• Support comes from neophobia in young
children
What is neophobia?
• Neophobic infants are more likely to reject new
foods in favour of those that are already familiar
to them.
• This suggests that we are predisposed to be
conservative in our food preferences (stick with
what we know is safe).
Why do we like chocolate?
 We have an innate preference for sweet things (Rozin,
1982).
Why?
 Sweetness indicates the presence of sugar which in turn
indicates calories needed for energy.
 Evidence from human biology that we are sensitive to
sugar.
 The nerve that runs from our tongue to our brain carries
more fibres that are sensitive to sweetness than any other
flavour sensation (i.e. bitterness, sourness or saltiness).
Support for innate sweet preference
Desor et al (1973)
• Investigated babies food preferences based on facial
expressions and sucking behaviour.
• New-born babies (only 1-3 days old) demonstrated
innate preference for sweet-tasting food.
• Rejected bitter tasting substances.
Why don’t we like bitter and sour?
• These taste receptors help us to identify food
that has gone off.
• Leads to the facial expression of ‘disgust.’
• This natural reaction is seen in human infants
and other primates.
• Suggests innate.
• This feeling leads to avoidance of bitter and
sour tasting foods.
Research
Meiselman et al (1989) – all cultures seem to prefer
sweet tastes to any other suggesting innate preference.
Bell et al (1973) – Eskimos in Alaska lack sweet foods
in their diet. However they are quick to accept sweet
foods into their diets when they come into contact with
them, even though they have no experience of them.
Supports the idea of an underlying human preference
for sweet foods.
Associative learning
“We are predisposed to learning preferences by associating foods
with the context and consequences of eating them.” (Birch, 1999).
1)More inclined to avoid foods that made us ill in the past.
2)Prefer flavours that have been previously paired with a preferred
sweet taste or with nutrients that supply us with energy e.g.
sugar.
These predispositions are highly adaptive as they reduce the
likelihood that young children will eat harmful substances (often
indicated by sour or bitter tastes), therefore increasing the
probability of their survival.
Taste aversion
• First found by farmers trying to rid themselves of rats.
• Difficult to kill rats using poisoned bait as they would
only take a small amount of any new food, and if they
became ill, would rapidly learn to avoid it.
• Learnt to associate taste of certain food with
symptoms (e.g. vomiting) caused by poisonous
substance, therefore developed an aversion to it and
would avoid it in the future.
Taste aversion
Garcia et al (1955) – first to study taste aversion in lab
Rats were given saccharin- flavoured water and shortly
after were exposed to radiation (which made them feel
ill e.g. nausea). When given the saccharin-flavoured
water again, they avoided it. Therefore had developed an
aversion to saccharin as they now associated it with
illness.
Evaluation of taste aversion
The development of taste aversions would have helped our ancestors to
survive because, if they were lucky enough to survive eating poisoned
food, they would not make the same mistake again.
Such aversions are very hard to shift – an adaptive quality designed for
survival.
How might smell/taste aversion play a role in morning sickness?
Often results in avoidance of particular foods from taste/smell
associated with nausea/vomit
Evaluation
Could early humans have been vegetarian?
Cordain et al (2006)
Argued that early humans consumed most of their calories from
sources other than saturated animal fats i.e. plant-based foods.
This has led to the suggestion that our distant ancestors were healthy
eaters and may even have been vegetarian.
However, evidence shows that all societies display a preference for
animal foods and fats (Abrams, 1987).
Also, if early humans were completely vegetarian would they have
been able to get sufficient calories from plants and grains in order to
survive?
Evaluation
It has been argued that not all food preferences are a product of
evolution.
A trait that is beneficial today (e.g. consumption of low
cholesterol foods) would not have evolved because of its
beneficial effects for our ancestors.
Our ancestors viewed saturated animal fats as important for
energy (and survival!) whereas today we view them as harmful
and try to avoid them in order to survive and stay healthy.
Evaluation: IDA
Cultural differences: Innate responses do not account for the
broad range of food likes and dislikes that develop beyond
infancy. Evolved factors important in food selection but these
are modified by our experience with different foods in our
culture.
Real-world applications: Research on taste aversion has been
helpful in understanding the food avoidance that can
sometimes occur during the treatment of cancer. Some cancer
treatments can cause gastrointestinal illness. When this illness
is paired with food consumption, taste aversions can result.
Pair task: IDA
In pairs, apply relevant IDA to the evolutionary explanations of
food preference.
Write your ideas down in the box on your worksheet.
Methodological issues
Ethical issues
Reductionism
Nature vs. Nurture
Plenary (K&U)
For each term or name in the table, colour code
whether it is linked to neural mechanisms in
eating behaviour or evolutionary explanations
of food preference.
Next lesson…
• Quiz.
• Brief run through of evolutionary
explanations for eating behaviour as a
class.
• Test (24 marks) – on all of topic so far.