HUNGER
Hunger is a good motivated behavior b/c it involves physiology & psychology at the same time! If people only ate to satisfy a physiological need, hunger would be a simple process. BUT…people eat not only to relieve hunger but they also eat to feel comforted, to socialize, or to relieve boredom. People also refuse to eat for a variety of reasons; to exert control, to lose weight, or to make a political statement.
The Physiology of Hunger Your brain automatically monitors your blood chemistry & your body’s internal state. The blood sugar glucose is a very important trigger for hunger…Increases in the hormone insulin (secreted by pancreas) diminish blood glucose, partly by converting it to stored fat. Signals from your stomach, intestines, & liver (re:glucose being deposited/withdrawn) signal your brain to motivate eating or not Extremes in blood sugar levels: – Hypoglycemia: blood sugar levels run too low via lack of food; feeling dizzy, weak, or shaky – Hyperglycemia: blood sugar levels run too high (diabetes) caused by cells in pancreas don’t metabolize carbs.
The Hypothalamus = The Appetite Center The lateral hypothalamus (LH): controls the desire to eat! {Large Hunger or desire to eat} – If electrically stimulated, well-fed animals begin to eat & will continue to eat w/o becoming satiated. – If the area is destroyed, even starving animals have no interest in food. The ventromedial hypothalamus (VHM): depresses hunger or controls satiety. {Very Minute Hunger or feeling full} - If stimulated an animal will stop eating or starve to death. -Destroy this area & the animal’s stomach & intestines will process food faster causing obesity.
Lesions near the VMH caused these rats’ triple weight gain!
The Appetite Hormones Insulin: Secreted by pancreas; controls blood glucose. Leptin: Secreted by fat cells; when abundant, causes brain to increase metabolism & decrease hunger. Orexin: Hunger-triggering hormone secreted by hypothalamus. Ghrelin: Secreted by empty stomach; sends “I’m hungry” signals to the brain. PYY: Digestive tract hormone; sends “I’m not hungry” signals to the brain.
The complex interaction of appetite hormones & brain activity helps to explain the body’s predisposition to maintain itself at a particular weight level.. Set point: point at which a person’s “weight thermostat” is supposedly set. When the body falls below this weight, an increase in hunger & a lowered metabolic rate acts to restore lost weight & the converse is also true. Basal Metabolic Rate (BMR): the body’s resting rate of energy expenditure. Some researchers doubt our bodies have preset tendencies to maintain optimum weight. Slow sustained changes in body weight can alter one’s set point & psychological factors also sometimes drive our feelings of hunger. Settling point: level a person’s weight settles in response to caloric intake & expenditure.
The Psychology of Hunger What psychological & cultural factors influence hunger? Body chem. & enviro. factors together influence not only when we feel hungry, but also what we hunger for…our taste preferences. -i.e.: Tense/Depressed? Do you crave starchy/carbs? Carbs help boost levels of the NT serotonin, which has calming effects. -Our preferences for sweet & salty are genetic & universal. Culture affects taste too! -Bedouins enjoy camel’s eye; N.Americans & Europeans shun horse, dog & rat meat, all of which are prized elsewhere.
The Ecology of Eating To a surprising extent, situations also control our eating…. *People eat more when eating with others! -Social influence affects our motivation to eat. -Business lunch, being with friends/family -U.S. = 3 square meals/day; -Euro=small breakfast, large lunch & late dinner – after 8pm Unit bias: occurs w/ mindlessness to increase our caloric intake. When available, we often select the larger portion sizes; if food is served in/on a larger plate or bowl, we take more & thus, eat more food.