1. Prepared by Jeffrey W. Grimm Western Washington University
PowerPoint Presentation for Biopsychology, 9th Edition by John P.J. Pinel
Prepared by Jeffrey W. Grimm
Western Washington University
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2. Why Do Many People Eat Too Much?
Chapter 12
Hunger, Eating,
and Health
Why Do Many People Eat Too Much?
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3. Copyright © 2014 Pearson Education, Inc.
Control of Eating
Is there a “set point” for the body’s energy reserves that determines when we eat?
The prevalence of eating disorders suggests that this may not be the case.
Over half of the adult population in the U.S. meets clinical criteria for obesity.
The average American consumes 3,800 calories per day—about twice the average requirement.
3 percent of U.S. adolescents suffer from anorexia or bulimia.
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4. Digestion, Energy Storage, and Energy Utilization
The purpose of eating is to provide the body with molecular building blocks and energy.
Digestion: breaking down food and absorbing its constituents
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5. Energy Storage in the Body
Energy is delivered to the body as lipids, amino acids, and glucose.
Energy is stored in the body as fats, glycogen, and proteins.
Fats are most efficient for energy storage.
One gram of fat stores twice as much energy as one gram of glycogen.
Fat does not attract and hold as much water as glycogen, and so provides denser energy storage.
Energy metabolism: chemical changes that make energy available for use
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6. Theories of Hunger and Eating: Set Points vs. Positive Incentives
The Set-Point Assumption
Hunger is a response to an energy need; we eat to maintain an energy set point.
Typical assumption: eating works like a thermostat; it turns on when energy is needed and off when the set point is reached.
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7. Glucostatic and Lipostatic Set-Point Theories of Hunger
If we eat to maintain an energy level (homeostasis), what is monitored?
Glucostatic theories: glucose levels determine when we eat
Lipostatic theories: fat stores determine how much we eat over long term (explaining why weight tends to be constant)
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8. Positive-Incentive Perspective
We are drawn to eat by the anticipated pleasure of eating.
We have evolved to crave food.
Multiple factors interact to determine the positive-incentive value of eating.
This accounts for the impact of external factors on eating behavior.
Adaptive Species-Typical Preferences
Sweet and fatty foods = high energy
Salty = sodium-rich
Adaptive Species-Typical Aversions
Bitter = often associated with toxins
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9. Factors That Influence What, When, and How Much We Eat
We tend to get hungry at mealtime.
As mealtime approaches, the body enters the cephalic phase, leading to a decrease in blood glucose.
Pavlovian conditioning of hunger has been demonstrated experimentally.
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10. Factors That Influence What, When, and How Much We Eat (Con’t)
Satiety: may stop a meal, “being full”
Satiety signals: food in gut and glucose in the blood can induce satiety signals.
Sham eating studies demonstrate that satiety signals are not necessary for meal termination.
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11. Factors That Influence What, When, and How Much We Eat
Appetizer effect: small amounts of food may increase hunger.
Serving size: the larger the serving, generally the more consumed.
Social Influences
Even rats eat more when in a group.
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12. Prader-Willi Syndrome: Patients with Insatiable Hunger
Symptoms
Food-related: insatiable appetite; extremely slow metabolism; eventual death in adulthood from obesity-related diseases
Other symptoms: weak muscles, small hands and feet, triangular mouth, stubbornness, feeding difficulties in infancy, tantrums, compulsivity, skin picking
Damage to or Absence of a Section of Chromosome 15
Study of the syndrome may lead to advances in understanding eating behaviors in humans.
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13. Who Needs to Be Concerned about Obesity?
Everyone: rates of obesity are increasing in most parts of the world.
Obesity is related to many other health problems.
Why is there an epidemic of obesity?
Evolution favored preferring high-calorie food, eating to capacity, storing fat, and using energy efficiently.
Cultural practices and beliefs promote consumption.
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14. Why Do Some People Become Obese While Others Do Not?
Energy Input Differences
Craving for high-calorie foods
Cultural norms
Energy Output Differences
Exercise
Diet-induced thermogenesis
NEAT (nonexercise activity thermogenesis)
Genetics interact with both energy input and output.
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15. Why Are Weight-Loss Programs Typically Ineffective?
Considering the leaky-barrel model, long-term weight loss will require a permanent lifestyle change.
Exercise also can make you hungry.
Often people eat more calories after the workout than they burned during the workout.
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16. Leptin and the Regulation of Body Fat
Leptin: a negative feedback fat signal
Hormone released by fat cells
Leptin receptors found in the brain
Ob/ob mice are three times normal weight.
Homozygous for a mutant gene ob
Lack leptin
Eat more, and store fat more efficiently than controls
Human Leptin Research
However, most obese humans have high leptin levels. Leptin injections help the few ob/ob humans.
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17. Treatment of Obesity: Serotonergic Agonists
Serotonin appears to increase short-term satiety signals associated with the consumption of a meal and decrease:
Urge to eat high-calorie foods
Consumption of fat
Intensity of hunger
Size of meals
Number of snacks and bingeing
Early serotonin agonists produced heart disease in some patients and were withdrawn from the market.
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18. Treatment of Obesity: Gastric Surgery
Gastric bypass and the adjustable gastric band create a smaller stomach.
Treatments are for extreme obesity.
These treatments are effective in some patients.
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19. Anorexia and Bulimia Nervosa
Voluntary self-starvation
Fatal in 10 percent of patients
Bulimia: bingeing and purging
The two illnesses have similar symptoms, and can be difficult to distinguish.
Distorted body image
Most often affects educated, affluent young females
Associated with obsessive-compulsive disorder and depression
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20. Anorexia and Positive Incentives
It is not clear whether anorexics find food less appealing.
Some evidence suggests the opposite.
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21. Anorexia Nervosa: A Hypothesis
A person out of homeostatic balance might find a full meal to be aversive.
Eating a meal would then lead to development of food aversions.
For example, feeding meals to famine victims sometimes leads to anorexia.
The implication is that anorexics should eat small amounts of food throughout the day as part of their therapy.
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