Biological explanations of eating behaviour

Neural mechanisms
1. Homeostasis
  1. Eating
    1. Increase BGL
      1. VMH activated
        Satiety
        Eating stops
        Decrease BGL
        LH activated
        Hunger
  2. Hetherington & Ranson - VMH lesions made rats over eat
    1. Han & Lin - lesioned VMH then force fed rats. Lesion didn't cause overeating higher set point already reached
  3. Anand & Brobeck - LH lesions stopped eating behaviour
    1. Neither killed rats, must have been stopped somehow - dual control theory
      1. LH lesions lower set point VMH lesions raise it - set point theory
    2. Powley & Keesey - starved rats and lesioned LH. Lesion didn't stop eating, lower point already reached
  4. Insulin & Glucagon maintain BSL. Bloodstream fat -> adipose tissue
2. Role of the hypothalamus
  1. PYY - screted after meals, suggests fullness
  2. Ghrelin - secreted by stomach, suggests hunger
    1. Also activates NPY neurones
      1. Marie et al - manipulated mice so NPY neurones not created, no change in feeding behaviour
  3. Leptin levels increase when plenty of adipose
    1. Insulin & Leptin reduced, NPY neurones stimulate orexigenic neurones
      1. LH stimulated - starting eating
    2. Insulin & Leptin increased, POMC neurones stimulate anorexigenic neurones
      1. VMH stimulated - eating stops
  4. NPY produced by abdominal fat. Vicious cycle where NPY causes more eating, producing more fat cells
    1. Individuals at risk of increased NPY treated to prevent obesity
  5. Gold - VMH lesions only produced overeating when including PVN
    1. Findings not replicated in humans
      1. In animals PVN lesion lead to increased feeding. In humans PVN detects food we need, may cause cravings
3. Neural control
  1. Amygdala used to select food based on experience
    1. Rolls & Rolls - surgically removed rats amygdala, they ate novel and familiar foods, unlike normal rats
      1. Can explain the behaviour of Klüver–Bucy suffers who have an eat anything attitude, including non food items. Food cues no longer represent reward
  2. Inferior frontal cortex recieves messages from the olfactory bulb
    1. Kolb & Wishaw - damage caused decreased eating due to less sensory information affecting taste
Evolutionary explanations of food preference
1. EEA - the environment where a species first evolved
  1. Adaptations to environment shaped food preferences
  2. Humans lived in hunter gather society with preference for easy high calorie food
    1. Men: Hunters. Women: childcare and foraging
  3. Low cholesterol preference not from EEA. No advantages
  4. Stanford - Chimps (mostly starved) go for the fattiest part of meat
    1. Abrams - All human societies show preference for animal fat. Universal adaptation
2. Taste preference
  1. Meat - packed with nutrients - catalyst for brain growth. Supplied AA and minerals
    1. Adapted for meat - larger than average duodenum, for protein breakdown
  2. Fatty foods - provided energy for survival
  3. Distaste for sour - associated with gone off food - source of bacteria
3. Taste aversion - evolutionary advantage
  1. Garcia et al - rats made ill by radiation after eating Saccharin (sweetener). Aversion developed from association
  2. Eating poison and being sick makes you unlikely to eat the same food in the future. Hard to shift
  3. Neese & Williams - Children's taste aversion to broccoli & brussels sprouts understood as they contain chemicals toxic to children
4. The medicine effect - preference developed for food eaten just before overcoming illness
  1. Assocaited with feeling better
5. Food neophobia - evolutionary tendency to avoid new foods
  1. Frost - Greater liking for familiar foods
  2. Bernstein & Webster - chemotherapy patients given novel ice cream before treatment. Aversion developed
    1. Hospitals now give patients novel and familiar foods
6. Cooking
  1. Wrangham et al - food cooking started 500,000 years ago. Good way to kill bacteria
  2. Lucas et al - cooking made food easier to chew, molar size decreased
7. Embryo protection hypothesis - morning sickness occurs in early stage of pregnancy during organ development
  1. Buss - Coffee, tea, meat & eggs most avoided
    1. Most common sources of bacteria

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Biological explanations of eating behaviour

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