Obesity - Biological theory

Question 1

Biological explanation

Answer 1

Belief that full understanding of thoughts, emotions and behaviour must include an understanding of their biological basis e.g genetics/neural explanations

Question 2

*Genetics

Twin studies

Answer 2

• The average heritability reported in twin studies is between 40-75%
• A meta analysis of 75,000 individuals found heritability estimates for BMI of 74% in MZ twins and 32% in DZ twins (Maes et al)
• Even when reared apart MZ are more similar than DZ that are reared together(Stunkard et al)

Question 3

Adoption studies

Answer 3

• Stunkard et al got information on 540 adult adoptees, their adopted parents and biological parents
• Showed a strong correlation between the weight category of adopted individuals and their biological parents weight category but no relation with adoptive parents

Question 4

*Neural

Hypothalamus

Answer 4

• Research has identified the arcuate nucleus which is a collection of neutrons that play a role in appetite and obesity
• It monitors circulating sugar levels in the blood and acts when energy levels are low
• When activated sends messages to other parts of the body creating the desire to eat + coordinates with energy utilisation so any malfunction can lead to overeating

Question 5

Leptin

Answer 5

• Hormone secreted by fat cells and acts to decrease feeding behaviour + promote energy expenditure
• Inhibits food intake by using leptin receptors in the appetite control centres in the brain
• Inhibits neuropeptide Y in the arcuate nucleus
• Disrupting to its signalling can result in obesity

Question 6

Thrifty gene hypothesis

Answer 6

Neel said in the past for humans it was often food or famine where they would have loads of food available or go hungry ; those who had large amounts of food then held reserves of body fat for when food was scarce again so could survive

Question 7

Advantage

Answer 7

People with this gene were efficient in the intake and utilisation of food making them fat giving them the energy needed to survive during famines

Question 8

Disadvantage

Answer 8

In todays society this gene is not useful as it promotes fat deposition for famine which never comes resulting in obesity and diabetes

Question 9

Genetic influences vary with age

Answer 9

Genetic contribution to BMI is not stable across a whole lifetime; a meta analysis(Elks et al) found heritability estimates varied according to age groups finding the figure higher during childhood which decreased in adulthood
May be due to greater gene expression during childhood as adults have more environmental contribution

Question 10

Advantage of biological explanation

Answer 10

Give an explanation that is seen as out of the persons control so less stigmatising in contrast to psychological ones that emphasises persons failing therefore making biological ones more ‘attractive’ and so offers hope of dealing with obesity based on remedial leptin injections

Question 11

Problem with thrifty gene

Answer 11

Speakman argues if this is correct then most of us should have this gene and so majority of humans be obese
Concerns about the obesity epidemic has been restricted to only a few societies where cultural habits have led people to eating fatty and sugary foods
Ng et al found more than half the worlds 671M obese people live in just 10 countries which can easily be explained by cultural factors rather than evolved adaptations