Biological Explanation For Obesity

Question 1

Neural explanation: serotonin

Answer 1

• obesity is associated with low-levels of serotonin
• signals to VMH when we are full
• hence low levels, leading to disinhibited eating
• could be due to stress, genetics or depression

Question 2

Neural explanation: dopamine

Answer 2

• associated with feelings of pleasure and wellbeing
• obese people have lower D2 receptors, therefore lower levels of dopamine
• (dont have enough dopamine to experience normal pleasure from eating so just eat more)
• attempt to increase dopamine, maximise pleasure center
  -> ultimately obesity is the outcome of a food addiction

Question 3

Evidence for serotonin

Answer 3

• Ohia et al:
• genetically engineered ‘knockout’ mice to have no functioning 2C receptors -> mice developed onset obesity

Question 4

Evidence for dopamine

Answer 4

• Spitz et al
• focused on DRD2 gene that codes for the D2 receptor
• found one version of the DRD2 gene was more prevalent in obese participants

Question 5

Obesity

Answer 5

A chronic disease that increases the risk of other diseases and so reduces life expectancy, BMI of over 30 = obese

Question 6

Twin studies

Answer 6

Nan et al ->
- conducted a meta-analysis of 12 twin studies involving over 8000MZ and 10,000DZ twins
- concordance rates ranging from 61%-80%

ISSUE: meta-analysis, different methods, not really comparable

Question 7

Adoption studies

Answer 7

• Stunkard et al
• gathered information on 540 adult adoptees, their adoptive parents and biological parents
• found that there was a strong relationship between the weight categories of adopted indivuals and their biological parents, but no with their adoptive parents

Genetics > environment

Question 8

Family studies

Answer 8

• Chaput et al
• stated concordance rates for first degree relatives are between 20% and 50% which indicates a moderate degree of heritability

Question 9

Polygenetic determination

Answer 9

(The specific set of polygenetic variants relevant for obesity in one individual is unlikely to be the same in another obese subject)
- Locke et al
- studied genomes of more than 300,000 individuals and identified 97 genes associated with variations in BMI
- 97 genes accounted for only 2.7% of BMI variation

Question 10

‘Thrifty gene hypothesis’

Answer 10

• Neel
• proposed theory that in human history species experienced ‘food or famine’
• those who gorged when food was available had the reserves of fat for when food became scarce so were more likely to survive
• therefore thrifty gene wouldve been adaptive

Question 11

Problems with ‘thrify’ gene hypothesis

Answer 11

• Ng et al
• more than half the worlds 671 million obese people live in 10 countries, suggest high levels of obesity found in these cultures can more easily be explained by cultural factors rather than evolved adaptions
• theory suffers from ethnocentrism

Question 12

Limitations of biological explanation

Answer 12

NATURE VS NURTURE
- only focuses on genes, might be more appropriate to take an interactionist approach such as the diathesis stress model

Biologically reductionist