Eating and Appetite

• Where does digestion begin?

  begins by chewing food and swallowing it, where it is stored and broken down in the stomach
• Where does digestion end?

  travels from stomach through small and large intestines, waste is disposed through the anus
• What is the set point theory of hunger?

  • each individual has an optimal level of energy resources (a set point)
  • bodies inherently seek to return to this set point, whihc is why we feel hunger. This is referred to as homeostasis
• How is the set point theory evolutionarily unlikely?

  Needs to cope with inconsistent resources in the environment, instead of just responding to energy defifcits
• How is the set point theory not supported by evidence?

  • Reductions in blood glucose needed to start a meal are substantial
  • Drinking a high calorie drink prior to meal time does not stop the meal, even though is restores BGL
• How does the set point theory ignore environmental factors?

  doesnt take into account the effects of learning, food preferences, and social factors
• What is the positive incentive theory?

  says that eating behvaiour is driven by anticipation, craving, and multiple factors
• What is anticipation in the PIT?

  • Animals driven to eat by the expected pleasure of eating
  • Expected pleasure = positive-incentive value.
• What is craving in the PIT?

  • Eating (and the perception of hunger) is initiated by craving.
  • This may be for something specific.
  • Enables you to take advantage of good food (when its available).
• What are the mutiple factors in PIT?

  • Flavour of the food.
  • Knowledge about the food (learning).
  • Time since last meal, amount of food in gut, blood glucose levels
• What is a conditioned taste preference?

  Learned preference for a specific taste due to pairing it with a positive or negative stimulus
• What is a conditioned taste aversion?

  Learned association between a specific taste and negative consequences
• How do animals show that food preferences can be socially aquired?

  animals will prefer a certain type of food if they’ve seen other animals eating it (clear evolutionary advantage. (poison/death, etc)
• How do we learn to eat vitamins and minerals?

  • injection of formalin (prompts a salt craving) vs. control (nothing) Control = Prefer banana (previously paired with sugar) Formalin = Prefer almond (previously paired with salt).
  • Demonstrates that animals can learn an association between neutral flavours and minerals even when they don’t need them
• Why do people have bad diets?

  • Harris et al., (1933): Thiamine (Vitamin B1) depleted rats. Learned to chose a complete diet and avoid a thiamine deplete diet
  • Effect weakened when there was a choice between 10 different diets
  • many diet options make it hard to establish which foods are useful
• How does pre-meal hunger initiate a meal?

  • Eating a meal stresses the body
  • Signals for a meal (e.g. time of day, smells) evokes a cephalic phase, causing insulin to be released and BGL to drop
  • Thus, hunger isn’t a cry for energy → body preparing for homeostasis disruption
• How does conditioned hunger inititate a meal?

  conditioned cues (such as brand logos, smells) trick you brain into thinking you are hungry, causing meal inititation
• How is the ventral medial hypothalamus involved in hunger?

  VMH is a satiety centre (inhibits eating), found lesions here leads to overeating and obesity (hyperphagia)
• What is VMH syndrome?

  • (1)Dynamic phase: excessive eating, weight gain
  • (2) Static phase: Body weight maintained. Overweight state returns following diet.

  VMH Syndrome rats will not work for food. Sensitive to unpalatable foods (finicky)
• How is the lateral hypothalamus involved in hunger?

  a feeding centre (disinhibits eating), lesions here leads to aphagia (stopping eating)
• What is LH syndrome?

  • (1)Aphagia if often accompanied by adipsia (cessation of drinking).
  • (2) Recovery is possible; tube feeding, milk soaked cookies, dry food pellets
• Why is the hypothalamus and hunger theory not valid?

  • VMH lesions in fact damaged the PVN. This region produces hyperphagia & obesity.
  • Hypothalamus regulates metabolism, not eating
• Is the stomach necessary for hunger?

  • Contractions caused by empty stomach correlated with Hunger (Cannon & Washburn, 1912)
  • But patients without stomachs still get hungry, shows stomach not necessary for hunger
• How did Koopmans (1981) investigate satiety signals in rats?

  • Transplanted an extra stomach & length of intestine into rats
  • Food injected into the stomach, which decreased eating even though the transplanted stomach has no functioning nerves
  • Satiety signal must have reached the brain through blood flow (Can’t have been nutrients as not absorbed by the stomach)
• What are peptides?

  Short chains of amino acids, function as hormones or neurotrasnmitters
• How are peptides involved in eating?

  • Ingested food stimulates receptors in the gastrointestinal tract to release peptides into the bloodstream
  • peptides travel to brain where they can send signals about satiety
• What is a satiety peptide?

  • Gibbs, Young & Smith (1973) -Injected peptide cholecystokinin (CCK) into the gut of hungry rats. Rats ate less food
  • CCK may cause nausea when full, causing you to stop eating
• What is leptin?

  Peptide that acts as a negative feedback singal to lower appetite and encrourage fat metabolism
• What was found about leptin in rats?

  • Low leptin mice ate much more, converted calories to fat more efficiently
  • Seeley & Woods (2003):Injections of leptin in obese mice results in reduced eating and reduced weight
• Can leptin be used to treat obesity in humans?

  • Humans typically have high, not low levels of Leptin
  • Leptin injections in obese people do not decrease eating or body fat.
  • however, some success in treating human obesity