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Energy can be stored as fat, glycogen, and protein. Energy is usually stored in the form of fat ... twice as much energy as glycogen. Glycogen attracts water ... – PowerPoint PPT presentation

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Title: This paper demonstrates:


1
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.

2
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

3
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

4
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5
Rat with a VMH lesion
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7
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

8
Motivation and HungerWashburn showed that
stomach contractions (transmitted by the balloon)
accompany our feelings of hunger (indicated by a
key press) Cannon, 1929
9
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?

10
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.

11
Seems there are multiple systems involved in the
control of hunger
  • Animals that dont produce ghrelin (knock out
    mice) eat normally
  • Cutting off nerve signals from liver have little
    effect on day to day eating
  • Lesions of medulla dont lead to long-term
    disturbances in eating

12
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14
Anorexia Nervosa
  • About 2.5 of North American student population
  • Mostly female
  • 10 to 20 times more likely.

15
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

16
  • 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

17
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

18
  • Some evidence dont experience rewards like
    everyone else
  • Sugar water didnt 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

19
  • 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

20
  • 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?

21
Positive incentive model of Anorexia Nervosa
  • Normally starvation increases the positive
    incentive qualities of food.
  • So what is going on?

22
Positive incentive model of Anorexia Nervosa
  • Eatingor its consequencescan be very aversive
    to people who have been starved.
  • they become nauseous, which leads them to avoid
    the foods that they have eaten.

23
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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