• Metabolism – body’s rate of energy utilization
    • Two-thirds of energy used goes to support basal metabolism, the resting, continuous metabolic work of body cells
  • Immediate energy supply information interacts with other signals to regulate food intake (hunger not necessarily linked to immediate energy needs)
  • Homeostatic mechanisms are designed to prevent people from running low on energy in the first place (organisms will not wait until last second to eat)
  • Many researches believe in a set point, an internal physiological standard, around which body weight is regulated (if weight is altered, homeostatic mechanisms will return body close to original weight)
  • Body has long term signals that adjust appetite and metabolism:
    • Signals that start and terminate a meal
      • Hunger not triggered by empty stomach
        • People with nerves cut to stomach or stomach surgically removed still reported feelings of hunger
      • Sensors in hypothalamus and liver monitor blood glucose concentrations
        • If glucose levels drop, liver converts stored nutrients back into glucose, producing a drop-rise glucose pattern
      • Humans display a temporary drop-rise glucose pattern prior to experiencing hunger
      • Walls of stomach and intestine stretch while eating, send nerve signals to brain to indicate fullness
        • Nutritionally rich food can produce full feeling quicker than equal volume of less nutritious food
      • Patients with removed stomachs can still experience satiety due to chemical signals
        • CCK (cholecystokinin) released into blood after eating, stimulates receptors that decrease eating
    • Signals that regulate general appetite and weight
      • Fat cells secrete leptin (hormone that decreases appetite) to regulate food intake and weight
        • Doesn’t directly cause fullness, but affects amount of satiety signals required
      • Obese people have ample leptin in blood due to fat mass, but brain appears insensitive to signals
    • Brain mechanisms
      • Many parts of brain play a role in regulating hunger and eating
        • Lateral hypothalamus triggers hunger
        • Ventromedial hypothalamus ends hunger
          • Both found to not directly affect only hunger, but other factors that would also affect it
      • Paraventricular nucleus (PVN) – cluster of neurons packed with receptor sites for various transmitters that stimulate or reduce appetite
        • When losing weight, less leptin secreted, transmitters for hunger become more active (explains why dieting causes hunger)
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  • Psychological Aspects of Hunger
    • Eating is positively reinforced by the good taste of food and negatively reinforced by hunger reduction
    • Beliefs about caloric content of food, and memory of when and how much we last ate also affect consumption
      • Amnesia patients accepted multiple lunches half four after each other, while non-amnesia did not
    • Attitudes, habits, and psychological needs also regulate intake
      • Women overestimate how thin they must be to meet men’s standards, while men overestimated how bulky they must be
  • Environmental and Cultural Factors
    • Food availability is most obvious environmental regulator of eating
    • Food taste and variety powerfully regulate eating
    • Classical conditioning associates smell and sight of food with taste, triggering hunger
  • Obesity
    • Genes and environment
      • Heredity influences basal metabolic rate and tendency to store energy as fat or lean tissue
      • Genetic facots account for 40-70% of variation in body mass
      • Experts believe obesity is due to abundance of inexpensive, tasty, high fat foods, a cultural emphasis on getting the best value (causing supersizing of menu items), and technological advances that decrease need for daily physical activity
    • Dieting and weight loss
      • Being fat alters body chemistry and energy expenditure, priming people to stay fat
        • Obese people have higher insulin levels, which convert glucose to fat
  • Eating Disorders
    • Anorexia nervosa – eating disorder involving a severely restricted food intake
      • Often perfectionists who strive to live up to lofty self-standards
    • Bulimia nervosa – eating disorder involving binge eating followed by a purging of the food
      • Often depressed and anxious, exhibit low impulse control, and lack a stable sense of personal identity and self-sufficiency
    • Caused by environmental, psychological, and biological factors
      • More common in industrialized countries in which beauty is equated with thinness
      • Genetic factors may create a predisposition toward eating disorders
      • Many researchers believe that physiological changes are a response to abnormal eating patterns
        • Once started, the physiological changes perpetuate eating irregularities

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