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This paper demonstrates:. 1. Understanding of the subject matter/topic of the paper. 2. The ability to evaluate the scholarship cited. 3. The ability to clearly communicate ideas. 4. The ability to use APA style. SET POINTS VERSUS POSITIVE INCENTIVES… WHAT, WHEN AND HOW MUCH WE EAT.

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this paper demonstrates
This paper demonstrates:
  • 1. Understanding of the subject matter/topic of the paper.
  • 2. The ability to evaluate the scholarship cited.
  • 3. The ability to clearly communicate ideas.
  • 4. The ability to use APA style.
set points versus positive incentives what when and how much we eat
SET POINTS VERSUS POSITIVE INCENTIVES… WHAT, WHEN AND HOW MUCH WE EAT
  • Outline:
  • 1. Digestion and Energy Flow
  • 2. Set-Point Theories v. Positive-Incentive Theories of Hunger and Eating
    • a. Set-point Theories
    • b. Positive-Incentive Theories
  • 3. Factors That Determine What, When and How Much We Eat
    • a. What We Eat
    • b. When We Eat
    • c. How Much We Eat
  • 4. Human Obesity
    • a. Why Do Only Some People Become Obese?
    • b. Physiological Factors in Obesity
  • 5. Anorexia Nervosa
digestion energy flow
Digestion & Energy Flow
  • The primary purpose of eating is to supply the body with the energy that it needs to survive
  • Energy is available in three forms
    • (1) lipids (fats)
    • (2) amino acids (broken down from proteins)
    • (3) glucose (simple sugar byproducts of carbohydrates)
  • Energy can be stored as fat, glycogen, and protein
    • Energy is usually stored in the form of fat
      • One gram of fat can contain twice as much energy as glycogen
      • Glycogen attracts water
physiology of hunger
Physiology of hunger
  • What is it that causes hunger? Is it the pangs of an empty stomach?
    • A. L. Washburn working with Walter Cannon intentionally swallowed a balloon.
    • The balloon was inflated and measured stomach contractions.
    • Washburn pressed a button whenever he felt hungry.
    • His stomach was contracting at these moments
slide8

Motivation and HungerWashburn showed that stomach contractions (transmitted by the balloon) accompany our feelings of hunger (indicated by a key press) Cannon, 1929

signals from stomach
Signals from stomach?
  • Stomach does release peptide hormones
  • One well studied peptide hormone is ghrelin
  • In lab animals blood levels of ghrelin
    • Increase with fasting
    • Decrease after a meal
  • In humans
    • injection of ghrelin increases eating
      • Also can increase thoughts of food
        • Elicited vivid images of food in some people
    • blood levels increase shortly prior to a meal
    • Gastric bypass decreases ghrelin secretion
      • Perhaps part of the reason it is successful?
blood glucose levels
Blood glucose levels?
  • Decreases in blood glucose can stimulate hunger.
  • Injecting animals with insulin
    • Too much gets stored
  • Inject with 2-DG
    • Deprives cells of real glucose
  • Both can increase eating behavior
  • How is blood glucose detected?
    • Some evidence there are detectors in the liver
      • Injecting 2-DG into the blood supply of the liver can increase eating
    • Also in the brain
      • Inject 5-TG (similar to 2-DG) into hindbrain and medulla can increase eating.
seems there are multiple systems involved in the control of hunger
Seems there are multiple systems involved in the control of hunger
  • Animals that don’t produce ghrelin (knock out mice) eat normally
  • Cutting off nerve signals from liver have little effect on day to day eating
  • Lesions of medulla don’t lead to long-term disturbances in eating
anorexia nervosa
Anorexia Nervosa
  • About 2.5% of North American student population
  • Mostly female
    • 10 to 20 times more likely.
physical signs and symptoms of anorexia include
Physical signs and symptoms of anorexia include:
  • Extreme weight loss
  • Thin appearance
  • Abnormal blood counts
  • Fatigue
  • Insomnia
  • Dizziness or fainting
  • A bluish discoloration of the fingers
  • Hair that thins, breaks or falls out
  • Soft, downy hair covering the body
  • Absence of menstruation
  • Constipation
  • Dry skin
  • Intolerance of cold
  • Irregular heart rhythms
  • Low blood pressure
  • Dehydration
  • Osteoporosis
  • Swelling of arms or legs
slide16

Emotional and behavioral anorexia symptoms

    • Refusal to eat
    • Denial of hunger
    • Afraid of gaining weight
    • Lying about how much food has been eaten
    • Excessive exercise
    • Flat mood (lack of emotion)
    • Social withdrawal
    • Irritability
    • Preoccupation with food
    • Reduced interest in sex
    • Depressed mood
    • Possible use of laxatives, diet aids or herbal products
anorexia nervosa1
Anorexia Nervosa
  • Anxiety
    • 80-90% of anorexics report anxiety problems prior to onset of the disease
  • May be a genetic component
    • Heritability estimate = 50%
  • Evidence for estrogen/testosterone effects
    • Onset after the start of puberty = estrogen may promote the disease
    • If male twin = less likely to get anorexia = testosterone affects prenatal organization of the brain
      • Thus testosterone produced by male twin may protect against anorexia
        • Female/female = high
        • Female/male = next
        • Male/female = next
        • Male/male = lowest
slide18

Some evidence don’t experience rewards like everyone else

    • Sugar water = didn’t rate it as enjoyable as control group
    • When playing a gambling game
      • Hidden number (1-10) = greater or less than 5?
        • +2$ correct
        • - 1$ incorrect
      • Control group = excited when correct; disappointed when incorrect
      • Previous anorexia = less responsive.
        • Also reward pathway in the brain was less activated
          • fMRI
slide19

Women respond differently to hunger than men do

    • Highshool students s allowed to each as much as they want from a buffet
      • Baseline
    • Later brought back after fasting for 24 hours.
      • Males ate faster and more than they did before
      • Females ate slower and less than they did before
slide20

Perhaps some of the symptoms of anorexia are symptoms of starvation

  • Keys study
    • 1950s
    • Men volunteered to decrease eating by half
    • Lost 25% of body weight
      • Became preoccupied with food
        • Collect recipes
        • Food hording
      • Erratic mood
        • Withdrawn
        • Lost interest in sex
        • Depressed
      • When allowed to eat they would dawdle over food
        • Take 2 hours to eat what previously would take minutes
      • After starvation was over some complained about body image
        • Sign of Anorexia?
positive incentive model of anorexia nervosa
Positive incentive model of Anorexia Nervosa
  • Normally starvation increases the positive incentive qualities of food.
    • So what is going on?
positive incentive model of anorexia nervosa1
Positive incentive model of Anorexia Nervosa
  • Eating…or its consequences…can be very aversive to people who have been starved.
    • they become nauseous, which leads them to avoid the foods that they have eaten.
positive incentive model of anorexia nervosa2
Positive incentive model of Anorexia Nervosa
  • Conditioned aversions develop to just about any foods and anorexics simply stop eating.
  • Treatment according to positive incentive model?
    • limit them to small meals
    • infusions of nutrients
      • until they recover enough to avoid the aversive consequences of eating a meal.
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