Biological Explanation for Obesity

• What is obesity?

  Individual is overweight with a BMI of 30 and over
• What does genetic explanations?

  Suggests obesity as some individual appear more genetically predisposed to become obese than others.

  Multiple genes making ind more prone to developing obesity
• Twin studies - genetic explanations

  ---> heritability ranges of 40% to 75%

  Maes et al - meta analysis of over 75000 individuals

  • heritability of BMI in identical twins were 74% and 32% in non identical twins
• Adoption studies

  Allows room for separation of influence of biology and environment

  Stunkard et al - studied 540 adoptees with their biological and adoptive parents.

  • strong correlation between weight of adopted child and biological parents
  • no correlation between weight of adopted child and adoptive parents

  Suggests genes play a large role in determining obesity
• Strength of genetic explanations

  Empirical support from twin and adoption studies suggesting genes influence obesity

  • Maes et al - twin
  • Stunkard et al - adoption
• Limitation of genetic theory to oppose previous strength

  Based on correlation and heritability

  Most research is based on correlation = no clear cause and effect

  Lacks clear causality as it doesnt fully explain why some individuals who are genetically more prone to obesity aren't obese

  Decreases validity
• Limitation of genetic theory

  Lacks temporal validity

  Explanations don't account for rapid rise in obesity. Suggesting genes aren't solely the cause of obesity.

  If obesity was 100% genetic there would be no increase
• Limitation of genetic theory

  Reductionist

  Focuses on biology. Obesity is multifactorial as it includes influences such as cultural and environmental and social factors such as dieting among friends and exercising
• What does neural explanations focus on?

  Hypothalamus

  Neurotransmitters

  • Serotonin
  • Leptin
  • Dopamine
• Hypothalamus

  Plays role in regulation of eating. Regulates metabolism and energy usage.

  Arcuate nucleus - collection of neurons in hypothalamus

  Overactivation of this may cause obesity by triggering desire to overeat when neurons signal low blood sugar which urges desire to eat
• Leptin

  Hormone secreted by fat cells that signal to brain when there's no need to eat.

  Lack of leptin (genetic mutation of ob gene) may lead to obesity because there will be lack of signals telling VMH that its full ---> overeating = obesity
• Serotonin

  Normally signals to VMH that person is at satiety

  Dysfunctions of serotonin system may be genetically inherited due to stress or other disorders e.g. depression - Booij

  When serotonin is low ---> creates inaccurate satiety signals to hypothalamus = disinhibiting eating behaviour

  Low serotonin may create cravings for energy rich foods - Wurtman
• Dopamine 


  Stimulates brain areas e.g. hypothalamus which then provides rewards for feelings of wellbeing and pleasure being associated with pleasure from eating

  Low dopamine will reduce pleasure in eating meaning overeating is attempt to activate pleasure that brain would normally provide
• Strength for neural explanations

  Scientific evidence

  Many studies use PET or fMRI scans to observe brain activity. Controlled research = increases credibility

  Wang - obese individuals had less dopamine D2 receptors in part of brain compared to normal weight individuals

  
  

  Strengthens validity by creating concrete and measurable evidence
• Limitation for neural explanations to oppose previous strength

  Limited causality in evidence

  Most studies are correlational = shows associations between brain activity and obesity

  But doesn't prove that abnormal brain activity causes obesity

  Meaning more research is needed to establish clear cause and effect
• Limitation for neural explanations

  Reductionist

  Focuses on biological and neurological factors of obesity.

  Ignores factors such as social, psychological or environmental.

  These may contribute to obesity

  • psychological factors e.g. stress may lead to overeating

  Decreases validity
• Strength for neural explanations

  Real world application

  Has resulted in treatment strategies such as medication to target brains reward pathway

  • e.g. drugs that reduce dopamine to release or block certain receptors is used to manage weight

  It works by reducing appetite = less overeating