Transcript Animated PPt - WordPress.com

Learning Objectives
• To briefly revise the neural mechanisms for
controlling satiation and hunger
• To outline research into the evolutionary
explanations of food preference.
Recap - what do the following
words mean?
Ghrelin
Insulin
Glucagon
VMH
LH
CCK
Ghrelin
• Hormone released from the stomach.
• The less food in the stomach - the higher the
level of ghrelin released
• Gastric bands lower levels of ghrelin
• It works directly on the hypothalamus and
‘switches on’ feeding behaviour.
Insulin
• Released from the pancreas
• Enables the body to convert glucose in the
blood to glycogen for storage.
• The pancreas may become unable to release
either enough insulin or become damaged.
These problems will lead to diabetes.
Glucagon
• This is the hormone released from the
pancreas that will turn stored glycogen back
to glucose.
• The glucose is then released into the blood
for use.
VMH
•
•
•
•
Ventro-Medial Hypothalamus.
This area of the brain inhibits feeding.
Research in rats quite conclusive.
If the rat’s VMH is damaged you will end
up with obese rats – the ‘stop’ signal no
longer works
LH - ‘GO GO GO’
• An area of the hypothalamus called the
Lateral Hypothalamus.
• This area stimulates feeding.
• Research on rats confirmed that if the LH is
damaged the rat stops eating (aphagia) as
the ‘on switch’ no longer works
CCK – STOP!
• Cholecystokinin is a hormone released from
the duodenum.
• It is released once the food has passed from
the stomach to the small intestine.
• It acts on the hypothalamus as a satiety
signal when there is food present.
Review: neural explanations for eating &
satiation
Hunger, Eating and Satiation: the process
Eating
Increase in
Ventromedial Satiety
blood glucose hypothalamus reached
activated
Hunger
develops
Lateral
Blood glucose Eating stops
hypothalamus levels drop
activated
Next…
Evolutionary explanations for
food preferences
11




The “ultimate explanation”
Eating behaviour that might
not make sense today may
have an evolutionary basis...
Our ancestors lived in an
Environment of Evolutionary
Adaptation (EEA) era
Natural selection favoured
adaptations geared
towards survival
The EEA
• EEA=environment of
evolutionary adaptation.
• This is the environment our
ancestors lived and evolved
in.
• We evolved from the African
savannah some 2 million
years ago.
• We survived because of our
ability to adapt to our
environment.
• Our ancestors passed these
adaptive genes to us, hence
the reason the human species
survived.
Evolutionary explanations of food preferences

Evolutionary theory suggests that organisms
should behave so as to maximise survival
and successfully reproduce to pass on their
genes (Barash, 1977).

Survival depends on number of things, one of
which involves remaining healthy by
managing to obtain sufficient nutrients to
meet demands of the body
14
Why do we eat some foods but not
others?
FOOD PREFERENCES
Nature
1
2
Nurture
3
4
5
6
7
8
9
10
Preference for high-calorie food
 It was adaptive for humans to learn
which foods have high nutritional value
(high-calorie), since calories are essential
to provide energy for the body to
function
 Those humans who learnt quickest
which foods would provide the most
nutrition were the most likely to survive
and reproduce.
17
Evolutionary explanations
Early diets
• Originally hunters and
gatherers who ate
animals and plants.
• We had a preference for
fatty foods because fat
was a vital energy
resource for survival
• This is the reason why
we still prefer high
calorie foods, although it
isn’t necessary for our
life styles nor our
survival.
Problems with studying this area
• Have to rely on fossil evidence.
• Also have to look at primates and extrapolate
evidence.
• Cannot use conventional scientific
methodology.
• Can observe living hunter-gatherer
societies/tribes.
• Food shopping behaviour shows gender
differences!!
Testing evolutionary explanations for food
preferences
• We can’t go back in time to see for sure
how our ancestors ate.
• So we compare preferences with those of
monkeys who face similar adaptive
problems today that we did 2 million years
ago.
• Craig Stanford observed Chimps in an
African national park:
– Chimps had similar problems to us 2 million
years ago in that meat is also scarce and where
they’re starved for meat.
– Therefore when they do manage a kill, they go
straight for the fattiest part: The brain and bone
marrow rather than nutritious flesh.
What is gustation?




This is our sense of taste.
Which tastes can humans detect?
We can detect sweet, sour, salt and bitter tastes.
Recently we have discovered that Umami is a taste quality
of food that we can detect - it is a meat or savoury taste.
(good source of protein foods)
https://www.youtube.com/watch?v
Lesson 2:
=eGioSei8ywI
Taste Aversion
Why are these little cuties
pulling faces?
Why survival benefit does
disliking sour tastes confer?
What survival benefit does
disliking bitter tastes confer?



Desor et al (1975) investigated babies food
preferences based on facial expressions and
sucking behaviour
Newborn babies demonstrate innate preference
for sweet tasting food
Babies reject bitter tasting substances
Preference for sweet foods

A sweet taste is often associated with
ripeness, a high concentration of sugar
and a quick fix of calories

A preference for sweet food/drinks that
would encourage consumption of ripe
fruit was probably advantageous to our
early ancestors (Rozin, 1982)
24
Evolutionary explanations
Preference for salty foods

Salt is essential for the body to function
properly


25
Infants about four months old seem to show
a marked preference for salty foods over
non-salty
At the age of two years, children reject foods
that do not contain the expected amount of
saltiness (Beauchamp, 1987)
Evolutionary explanations



Sweet food = fruit = natural fructose
content = energy
Bitter = poison
Neophobia = fear of new foods
(unknown =>possibly dangerous)




Davis (1928,1939) observed choices of children
living in a paediatric unit
Found that young children had an innate ,
regulatory mechanism and make healthy food
choices
BUT they could only do so if healthy food was
actually available!!!
So food choice changed over time based on
the environment
Why don’t we like bitter and
sour?
These receptor help us identify food that
has gone off
Leads to the facial expression of ‘disgust’
This is seen in human infants and other
primates
Suggests innate
This feeling leads to avoidance
Evidence supporting
evolution of bitter taste
aversion
Sandell and Breslin (2006) screened 35 adults for the
hTAS2R38 bitter taste receptor gene. The participants were
given a diet that contained vegetables with Glucosinolates.
Glucosinilates, are found in broccoli and Brussels sprouts and
when taken at really high doses can be toxic. Glucosinolate
also gives these vegetables their bitter taste.
Participants with the sensitive form of the gene found the
vegetable 60% more bitter then the insensitive form of the
gene.
Bait Shyness : Association
Bait Shyness: Rats given poison were not
being killed as they only took a small
amount, got ill and then associated the
illness with the bait.
Garcia (1955) gave saccharin to rats just
before exposing them to radiation. They
found after exposure the rats developed an
aversion to saccharin.
Adaptive Advantage of Taste
Aversion
Taste and odour can be linked to taste
aversion.
The association can occur up to 24 hours
after the consumption of food. If you ever got food
poisoning from a restaurant, would you go back?
Why would this be advantageous to our
ancestors?
Taste aversion: Why we prefer
certain tastes to others.
• Humans learnt that certain foods are better for health.
• They therefore chose nutrient rich food and developed
an aversion for foods that didn’t enhance their chances
for survival.
• This was confirmed in lab tests on rats. Farmers for
example found that when they tried to poison rats, it
wasn’t useful as they would only eat small amounts of
poison, which would make them sick. They would
therefore associate ill health with the poison and
therefore developed an aversion for it.
• Detecting toxins: Our bitter taste evolved as a way to
detect poisons in plants = ensure survival.
Commentary on taste aversion
• Seligman supported the idea that we
avoided certain types of food because
they didn’t enhance our chances of
survival. He called this “biological
preparedness”.
• This was supported by research on
cancer patients undergoing chemo
and radio therapy (Bernstein &
Webster)
– When gave novel tasting ice cream prior
to treatment, people developed an
aversion to it.
– The body associates that taste with
illness and therefore creates an aversion
so that it isn’t eaten again.
Medicine effect
If we associate a food with recovering from
an illness we may have preference for that
food.
Garcia et. al (1955) Rats who were given a
distinctive flavour when given thiamine
injections developed a preference for that
flavour.
Commentary: Supporting & opposing
diet preferences
• Gibson & Wardle confirmed the idea that our ancestors preferred
calorie rich food.
– In their research, they allowed children to choose fruit and
veg.
– Findings: Children chose potatoes & bananas which are very
high in calories. This isn’t because they were sweet or
nutritious, but because they had the most calories.
• Cordain et al: Suggested the perhaps our ancestors were
vegetarian as originally we consumed most of our calories from
non-animal resources.
• Abrams the anthropologist opposed this and said that evidence
shows that all societies show a preference for animal foods and
fats. Also, grains and plants available wouldn’t have been
sufficient for our ancestors to survive from.
Morning Sickness
• This is thought to be an evolutionary hang-over. It
is thought that it developed to protect the early
stages of foetal development (when all the organs
were forming). It stopped potentially dangerous
toxins from being ingested by the mother to be.
• Caffeine is one thing that pregnant women can
stop liking in the early stages.
• Now with nutritional information and excellent
healthcare (in UK) morning sickness is not
useful!!
Preference for meat
• Quality of plant foods declined (due to
receding forests 2 mill years ago) =
preference for meat
• Fossil evidence: Ancestors ate mostly
animal organs such a liver, kidneys &
brain (extremely rich in nutrients).
• This helped our brains to evolve
according to our need to adapt to the
environment.
• Without meat, we wouldn’t have been
able to grow our brains and therefore
adapt to our environment and survive
until today (Milton 2008)
We cannot look at this from just a
biological viewpoint.
Cultural transmission of food
preferences is very important.
Then technically, we should all
have the same food preferences,
no?
• Yes, that’s true:
– We know that all children love sweet foods and
most of us have to control the amount of fatty
foods we eat in order to maintain health
– But culture and food experiences also play a
part.
– However, our innate preferences are universal,
they are just refined by our experiences.
Avoidance of food poisoning
• Cultural transmission of the use of spices is very
important. Onion and garlic are excellent at killing
bacteria in food.
• We know what food smells/tastes like when it has
gone off (detected by our sour and bitter taste
buds).
• We are also taught which foods are good/bad for
us.
• Food neophobia - fear of new food. Stops us
eating anything dodgey!!
Summary:
• A sweet taste is often associated with ripeness, a high concentration of sugar
and a quick fix of calories
• A preference for sweet food/drinks that would encourage consumption of ripe
fruit was probably advantageous to our early ancestors (Rozin, 1982)
• Salt is essential for the body to function properly and Infants about four
months old seem to show a marked preference for salty foods over non-salty
• At the age of two years, children reject foods that do not contain the expected
amount of saltiness (Beauchamp, 1987)
•
•
•
•
Newborn babies demonstrate innate preference for sweet tasting food
Babies reject bitter tasting substances
Sweet food = fruit = natural fructose content = energy
Bitter = poison
Evaluation
Strengths
Weaknesses
gives an explanation that can account
for both nature and nurture
Reductionist and determinist (eating is
caused by events happened years ago)
can explain innate food preferences
difficult to falsify, so questionable
validity
focus on ultimate rather than
proximate causes could provide more
effective intervention strategies
has human evolution stopped or are
we still adapting?
Discuss two or more evolutionary explanations of food
preference (24 marks)