Unformatted text preview: Etiology of
Obesity A Cascade of
Hunger Physiological need to eat, experienced as drive to obtain food
Triggered by chemical messengers originating & acting in the brain, esp. the hypothalamus
Neuropeptide Y appears to be strong appetite stimulant, esp for carbohydrate
rich foods Factors Affecting Hunger
Factors Nutrients in bloodstream
Size & composition of preceding meal
Customary eating patterns
Physical & mental disease states Adaptation of Hunger Response
Adaptation When intake is limited, hunger may diminish after a few days, BUT…
At some point, with continued deprivation, (and in the absence of illness affecting appetite) hunger returns with a vengeance
Stomach doesn’t actually shrink except in chronic starvation Hunger vs Appetite
Hunger Appetite could be defined as the psychological desire to eat
Appetite is more of a learned phenomenon
Endorphins (endogenous opiates – brain’s pleasure chemicals) are released on seeing, smelling, or tasting delicious food – believed to enhance drive to eat or continue eating
Social factors can influence appetite “Stop” Signals Satiation: perception of fullness that builds throughout a meal, eventually causing a person to stop eating. Natural determinant of how much food is consumed at one sitting.
Satiety: perception of fullness that lingers in the hours after a meal & inhibits eating until the next mealtime. Natural determinant of time between meals. Satiety
Foods Genetics & Obesity: The Evidence
Genetics Chance of becoming obese is 60% with one obese parent, 90 % if both parents obese
Adopted children tend to be similar in weight to biological parents, not adoptive parents
Identical twins are twice as likely to weigh the same as fraternal twins, even when reared apart More Evidence for Genetics
More When given 1000 extra calories/day for 100 days, some people gain 30 lbs while others gain less than 10 lbs. Some people lose more weight faster than others on comparable exercise regimens.
Discovery of leptin & the ob gene
Leptin: hormone produced by adipose tissue & linked to appetite & body fatness Genetically
Gene for Leptin Genetically
Gene for Leptin Receives Leptin No Leptin A Model
Fatness Leptin in Humans
Leptin Suppresses action of neuropeptide Y
Most obese people have elevated leptin concentrations already, & injections have no effect on appetite
Leptin receptors may become less responsive
Leptin appears to have other regulatory roles in the body, also Set-Point Theory
Set-Point Phenomenon of weight regain suggests that body chooses weight it wants to be and defends that weight by regulating eating behaviors & hormonal actions
Setpoint mechanism seems to trigger change in metabolic energy expenditure in the direction that restores initial body weight Other Obesity Theories
Other Enzyme theory: Based on action of LPL (lipoprotein lipase), which enables fat cells to store triglycerides. Concentrations increase as fat cells become larger. Which comes first, elevated LPL or larger fat cells?
Fat Cell Number: difficulty of losing weight may be due to excess number of fat cells. Prevention of formation of extra fat cells during childhood is suggested best approach. More Obesity Theories
More Adaptive thermogenesis: appears to occur in many tissues throughout the body. Consists of using energy to produce heat, which is basically a way to expend excess energy. When energy intake is low or body fat diminishes, heat production decreases to conserve energy.
In many obese people, no change in energy use occurs after eating.
Overall, obese people do not expend less energy than normal weight people on a daily basis. In fact, actually expend more. Behavioral Theories of Obesity
Behavioral External Cue Theory Rats fed “cafeteria diet” become obese
Availability & appeal of high fat foods could contribute to obesity
Stress can lead to overeating for many individuals, while having opposite effect for others Physical Inactivity Obese people less often engage in planned exercise (which comes first?) ...
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- Winter '11
- Nutrition, Malnutrition, Appetite, Leptin, obese people