Download The role of learning.

The role of learning.
Babies are born with taste receptors for
sweet, sour, salt, bitter and umami taste
qualities.
They like sweet tastes, and in fact sweet
foods are effective in reducing distress in
babies (Benton, 2002) This leads us to ask
whether we have innate (genetic) food
preferences.
Birch (1999) proposes that we are not
born with innate (genetic) food
preferences, but with an innate ability
to associate food tastes and smells
with the consequences of eating that
food. In this way we learn from
experience the foods that are good
for us and those which are not.
Food neophobia is widespread in the
animal kingdom as a basic survival
mechanism. Neophobia was also found in
babies and children although it decreases
with age.
Birch and Marlin found that exposure of two
year olds to a new food over 6 weeks increased
preference for that food, a minimum of 8-10
exposures was necessary for the dislike to
change to a preference. The children learn the
food is safe.
Birch’s proposal that we inherit an ability
to make such associations suggest an
interaction between nature and nurture.
We learn through experience what is
good for us (nurture) but that learning
depends upon brain circuits that are
innate (nature)
Parents attitudes and
food preference.
Parents, usually the mother, provide food
for the child. Therefore the mothers
attitude will affect the child’s
preferences.
As expected, there is a significant
correlation between the diets of mothers
and children (Ogden, 2007).
Nicklaus et al: Investigated the
correlations between food preferences at
2 and 22 in a longitudinal study of French
children.
Although there were only low correlations
between overall diet at age 2 and adult
diet, for about 50% of dietary items
there was a clear association between
childhood and adult preferences especially
for cheese and vegetables.
Once the child starts school, peers become more
important. Studies have shown that modelling using
admired peers can increase consumption of fruit
and vegetables (lowe, Dowey and Horne, 1998)
Children are also exposed to widespread food
advertisement on television to make the food more
attractive. This can be effective in developing
preferences, but unfortunately advertised food
tends to be high in carbohydrates and fat
contributing to childhood obesity.
Preference for meat decreases in females as
they got older, possibly due to ethical and
health concerns. There was clear links between
childhood food preferences and adult diet but
there were also changes suggesting other
factors are involved.
Adult preferences were assessed by
questionnaires and interviews which raises the
problem of social desirability bias as
participants may have given ‘healthier answers’
Mood.
Studies which investigate the effect of
mood and distress on eating often look for
evidence of either hypophagia (excessive
under eating) or hyperphagia (excessive
over eating) as well as changes in patterns
of consumption and food preferences.
Ogden suggests that dieters who overeat in
response to low mood may be seeking to
mask their negative mood with a temporary
heightened mood induced by eating.
Unfortunately this increase in serotonin levels
only occurs when we take in pure
carbohydrates, which is extremely rare. The
presence of even a small amount of protein as in
chocolate prevents the tryptophan entering the
brain and so serotonin levels will not change.
The serotonin hypothesis is unlikely to explain
the antidepressant effects of high
carbohydrate diets.
The serotonin Hypothesis: Carbohydrates such as chocolate contain the amino acid- Tryptophan.
This is usually used by the brain in the manufacture of the neurotransmitter serotonin.
Low levels of serotonin are associated with depression. It has been proposed that people with
stress or depression take in carbohydrates because it leads to increased levels of serotonin in the
brain which reduced their depression.
The opiate hypothesis: opiate neurotransmitters such as enkaphlin and beta-endorphin are
released from neurons and act at synapses with opiate receptors. Opiates produce pleasurable
feelings and euphoria. It seems likely the brains opiate pathways are part of our reward system,
a network of pathways that control our feelings of pleasure and reward. This reward system is
activated by natural rewards such as food and drink.
Mood.
Grigson: found that opiate drugs (e.g.
Heroin) increase food intake and increase the
perceived tastiness of food.
Blocking the endorphin system with the drug
naloxone reduces food intake, especially
sweet foods and supresses thoughts about
food. This shows the system is involved in
feeding regulation.
Because food is so vital we are very efficient
at learning associations between taste and
consequences (taste aversion) this applies to
positive effects as well- we learn to associate
the mood-improving effects of
carbohydrates with the sweet taste so when
we taste the food, we have expectations
about the consequences.
Glucose reliably improves performance on
cognitive tasks. However if people are given a
glucose drink but told it’s a placebo then the
effect disappears. Expectations override the
actual intake of glucose.
The sweet taste of a glucose solution
immediately produce a release of insulin from
the pancreas gland, anticipating a rise in blood
glucose levels. This happens even with drinks
sweetened with saccharine, a compound that is
not processes by the body.
However we have learnt that sweet tastes
usually mean glucose, so our body prepares
itself. Anticipation and expectation on the basis
of learning and experience affect out response
to it.
Culture.
Significant differences in diets across
cultures. This is often due to availability
of certain foods. Globalisation of the
food market means that even remote
communities food choice is increasing.
Wardle et al, surveyed the diets of
16,000 young adults across 21
European countries and found that in
general the number eating a basic and
healthy diet was low ( females doing
better than males)
•
People in the Mediterranean
countries eat more fruit and
vegetables that England and
Scotland.
•
People in Scandinavian counties eat
the most fibre, people in Portugal,
Italy and Spain eat the least.
Leshem: compared Bedouin Arab women living in
a desert encampments with those now living in
urban environments, and also with a group of
urban Jewish women.
The diet of urban Bedouins was similar to that
of the desert living Bedouins (despite the access
to a far greater range of food in the urban
settings) a much high intake of carbohydrates,
proteins and salts that the Jewish group.
In a later study Leshem found that the diet of a
Muslim community living in the same urban
setting as a Christian group was much higher in
carbohydrates, protein and salt that the
Christian community, although body mass was the
same.
Conclusion: even with equal access to a range of
foods, different ethnic groups have different
diets, demonstrating the influence of culture
and dietary history on food preferences.
Issues and debates:
Reductionist:
Biological explanations, especially the
evolutionary approach imply that much of
our diet is determined by nature rather
than nurture (genetics rather than
environment) this ignores cultural and
social changes in food availability and
choice over the years of human evolution.
The study of feeding behaviour and its
disorders has focused largely on western and
other industrialised societies. It has ignored
third word countries whose main aim is to
avoid starvation rather than cope with obesity.
This is an example of research that is
culturally biased.
Diet can show clear cultural variations, as Leshem’s work demonstrates. However we
cannot conclude that these are environmental or ‘nurture’ effects rather than
inherited tendencies (nature) where groups such as the Bedouin have lived in the
same environment for many generations, it may be that their diet today is a mixture
of innate factors and culturally transmitted preferences.