Problems with Set-Point Theories

Problems with Set-Point Theories

• Variability of body weight• Set points and health– Free-feeding does not lead to optimum health– Positive effects seen with caloric-restriction

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More Problems…

• Altering metabolism• Diet-induced thermogenesis – increases in

body fat increase body temperature

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Why do we care?

• Can control our body weight• Then why is there an obesity epidemic?

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Why Is There an Epidemic of Obesity?

• Evolution favored preferring high calorie food, eating to capacity, storing fat, & using energy efficiently

• Cultural practices and beliefs promote consumption

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Mutant Obese Mice and Leptin

• Mice are 3X normal weight– Lack leptin, a hormone produced by fat cells

• Leptin – a negative feedback fat signal

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Insulin: Another Negative Feedback Signal

• Like leptin, – levels correlated with body fat– receptors found in the brain– reduces eating at levels too low to be aversive or

to affect blood glucose• Insulin deficiency leads to hyperphagia, but

not obesity – food not converted to fat in the absence of insulin

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Drastic Measures

• Wiring jaw shut• Stapling stomach• Gastric Bypass Surgery

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Anorexia nervosa

• A disorder of under consumption of food• Weighs 85% or less• Affects puberty, menstruation, sex drive • Associated with depression, irritability,

withdrawal and peculiar behaviors

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What causes Anorexia?

• No single known cause• Culture • Families• Life changes or stressful events• Personality traits• Biology

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More on biology and psychology

• Serotonin (high and low)• Autoimmune response to melanocortin

peptides• “Perceive” themselves as larger• Lack overconfidence bias• Poor cognitive flexibility, attentional biases

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Anorexics are ambivalent about food

• Cephalic-phase response• Preoccupied with food• Disgusted by sweet and fatty tastes• Feel ill after a meal

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Anorexia and Positive Incentives

• Decline in the positive-incentive value of eating food vs. interacting with food

• Starvation normally triggers a radical increase in the positive-incentive value of food

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Meals

• Taste aversions that reduce the motivation to eat

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Bulimia Nervosa

• A psychological condition in which the subject engages in recurrent binge eating followed by an intentional purging (i.e. vomiting, laxatives, diuretics, excessive exercise, etc.)

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Causes and Factors

• Lack of control• Caucasian groups• Women: 90%• Activities that emphasize body type• Anxiety and other mood disorders

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