Eating

• Digestion


  The gastrointestinal process of breaking down food and absorbing its constituents into the body
• Hunger


  Increases the probability of eating
• Eating


  To supply the body with the molecular building blocks and energy to survive and function
• Digestion


  Puts food into one of its two holes—the one with teeth—and passes the food along its internal canal so that the food can be broken down and partially absorbed from the canal into the body
• Gut microbiome

  The bacteria and other organisms that live inside our gastrointestinal tract
• Forms of energy delivered as a consequence of digestion

  • Lipids (fats)
  • Amino acids (the breakdown products of proteins)
  • Glucose (simple sugar, the breakdown product of carbohydrates: starches and sugars)
• The body uses energy nonstop, but consumption is periodic
• Energy storage in the body

  To store energy for use in the intervals between meals
• Forms of energy storage in the body

  • Fats (most of the body's energy)
  • Glycogen (very little)
  • Proteins (very little)
• Glycogen


  Stored in the liver and muscles, converted into glucose, a usable source of energy
• A gram of fat can store almost twice as much energy as a gram of glycogen
• Glycogen, unlike fats, attracts and holds substantial quantities of water
• Phases of energy metabolism

  • The cephalic phase (preparatory phase)
  • The absorptive phase (the energy absorbed into the bloodstream from the meal is meeting the body's immediate energy needs)
  • The fasting phase (all of the unstored energy from the previous meal has been used and the body is withdrawing energy from its reserves to meet its immediate energy requirements)
• Insulin


  Promotes the use of glucose as the primary source of energy by the body, promotes the conversion of bloodborne fuels to forms that can be stored, and promotes the storage of glycogen, fat, and proteins
• Glucagon


  During the fasting phase, characterized by high blood levels of glucose, no high levels of insulin, glucose stops being the body's primary fuel, promotes the conversion of glycogen and protein to glucose, and promotes the release of free fatty acids and their conversion to ketones
• Set-point assumption


  After a meal, a person's energy resources are near their set point, and decline as the body uses energy to fuel its physiological processes; when the level of the body's energy resources is below the set point, the person is ready to eat; when the level of the body's energy resources is on its set point, the person feels satiated
• Set-point mechanism


  • Defines the set point
  • Detects deviations from the set point
  • Elicits compensatory effects in the opposite direction to eliminate the deviations
• Glucostatic theory


  The assumption that eating is regulated by a system designed to maintain a blood glucose set point
• Lipostatic theory


  Every person has a set point for body fat, and deviations from this set point produce compensatory adjustments in the level of eating that return levels of body fat to their set point
• Set-point theories of hunger and eating have three major weaknesses: they are inconsistent with basic eating-related evolutionary pressures, they fail to recognize the major influences on hunger and eating of such important factors as taste, learning, and social influences
• Positive-incentive perspective


  Humans and other animals are not normally driven to eat by internal energy deficits but are drawn to eat by the anticipated pleasure of eating
• Positive-incentive value


  The pleasure of a behavior
• According to the positive-incentive perspective, it is the presence of good food, or the anticipation of it, that normally makes us hungry, not an energy deficit</b>
• Leptin


  A peptide hormone released by fat cells that acts as a negative feedback signal to decrease appetite and increase fat metabolism
• Leptin levels are more closely correlated with subcutaneous fat (fat under the skin) than with visceral fat (fat stored around the internal organs of the body), which is more common in males and poses a greater threat to health
• Neuropeptide Y and melanocortins


  Two classes of neurons that leptin receptors are located on
• Elimination of leptin receptors in the melanocortin system produces only a slight weight gain
• Serotonergic agonists


  Reduce food consumption in humans and non-human subjects, produce long-term satiety signals based on fat stores, and increase short-term satiety signals associated with the consumption of a meal
• Gastric surgery


  Extreme treatment for extreme obesity, including gastric bypass (more effective) and adjustable gastric band procedures (can be removed)
• Anorexia nervosa


  A disorder of underconsumption, characterized by reduced metabolism
• Bulimia nervosa


  Characterized by periods of not eating interrupted by bingeing, followed by efforts to immediately eliminate the consumed calories from the body by voluntary purging or by extreme exercise
• If individuals with bulimia nervosa are underweight, they are considered to have binge-eating or purging anorexia
• Treatment for bulimia nervosa includes addressing irritation and inflammation of the esophagus, vitamin and mineral deficiencies, electrolyte imbalance, dehydration, and acid reflux