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



Outline:
1. Digestion and Energy Flow
2. Set-Point Theories v. Positive-Incentive Theories of Hunger
and Eating



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. Set-point Theories
b. Positive-Incentive Theories
a. Why Do Only Some People Become Obese?
b. Physiological Factors in Obesity
5. Anorexia Nervosa
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
Rat with a VMH lesion
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
Motivation and Hunger
Washburn showed that stomach contractions (transmitted by the balloon)
accompany our feelings of hunger (indicated by a key press) Cannon, 1929
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?


Decreases in blood glucose can stimulate hunger.
Injecting animals with insulin


Inject with 2-DG



Too much gets stored
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




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 longterm disturbances in eating
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:


















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

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 Nervosa

Anxiety


May be a genetic component


80-90% of anorexics report anxiety problems prior to onset of the
disease
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

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

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


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

Take 2 hours to eat what previously would take minutes

Sign of Anorexia?



When allowed to eat they would dawdle over food

After starvation was over some complained about body image
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 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 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.