Biological explanations of eating behaviour

Biological explanations of eating behaviour

1. Neural mechanisms

   • Homeostasis
     • Eating
       • Increase BGL
         • VMH activated
           • Satiety
             • Eating stops
               • Decrease BGL
                 • LH activated
                   • Hunger
     • Hetherington & Ranson - VMH lesions made rats over eat
       • Han & Lin - lesioned VMH then force fed rats. Lesion didn't cause overeating higher set point already reached
     • Anand & Brobeck - LH lesions stopped eating behaviour
       • Neither killed rats, must have been stopped somehow - dual control theory
         • LH lesions lower set point VMH lesions raise it - set point theory
       • Powley & Keesey - starved rats and lesioned LH. Lesion didn't stop eating, lower point already reached
     • Insulin & Glucagon maintain BSL. Bloodstream fat -> adipose tissue
   • Role of the hypothalamus
     • PYY - screted after meals, suggests fullness
     • Ghrelin - secreted by stomach, suggests hunger
       • Also activates NPY neurones
         • Marie et al - manipulated mice so NPY neurones not created, no change in feeding behaviour
     • Leptin levels increase when plenty of adipose
       • Insulin & Leptin reduced, NPY neurones stimulate orexigenic neurones
         • LH stimulated - starting eating
       • Insulin & Leptin increased, POMC neurones stimulate anorexigenic neurones
         • VMH stimulated - eating stops
     • NPY produced by abdominal fat. Vicious cycle where NPY causes more eating, producing more fat cells
       • Individuals at risk of increased NPY treated to prevent obesity
     • Gold - VMH lesions only produced overeating when including PVN
       • Findings not replicated in humans
         • In animals PVN lesion lead to increased feeding. In humans PVN detects food we need, may cause cravings
   • Neural control
     • Amygdala used to select food based on experience
       • Rolls & Rolls - surgically removed rats amygdala, they ate novel and familiar foods, unlike normal rats
         • Can explain the behaviour of Klüver–Bucy suffers who have an eat anything attitude, including non food items. Food cues no longer represent reward
     • Inferior frontal cortex recieves messages from the olfactory bulb
       • Kolb & Wishaw - damage caused decreased eating due to less sensory information affecting taste

2. Evolutionary explanations of food preference

   • EEA - the environment where a species first evolved
     • Adaptations to environment shaped food preferences
     • Humans lived in hunter gather society with preference for easy high calorie food
       • Men: Hunters. Women: childcare and foraging
     • Low cholesterol preference not from EEA. No advantages
     • Stanford - Chimps (mostly starved) go for the fattiest part of meat
       • Abrams - All human societies show preference for animal fat. Universal adaptation
   • Taste preference
     • Meat - packed with nutrients - catalyst for brain growth. Supplied AA and minerals
       • Adapted for meat - larger than average duodenum, for protein breakdown
     • Fatty foods - provided energy for survival
     • Distaste for sour - associated with gone off food - source of bacteria
   • Taste aversion - evolutionary advantage
     • Garcia et al - rats made ill by radiation after eating Saccharin (sweetener). Aversion developed from association
     • Eating poison and being sick makes you unlikely to eat the same food in the future. Hard to shift
     • Neese & Williams - Children's taste aversion to broccoli & brussels sprouts understood as they contain chemicals toxic to children
   • The medicine effect - preference developed for food eaten just before overcoming illness
     • Assocaited with feeling better
   • Food neophobia - evolutionary tendency to avoid new foods
     • Frost - Greater liking for familiar foods
     • Bernstein & Webster - chemotherapy patients given novel ice cream before treatment. Aversion developed
       • Hospitals now give patients novel and familiar foods
   • Cooking
     • Wrangham et al - food cooking started 500,000 years ago. Good way to kill bacteria
     • Lucas et al - cooking made food easier to chew, molar size decreased
   • Embryo protection hypothesis - morning sickness occurs in early stage of pregnancy during organ development
     • Buss - Coffee, tea, meat & eggs most avoided
       • Most common sources of bacteria