Answer to Question 1
Some people eat to live and others live to eat.. People who eat primarily in response to hunger are responding physiologically to the need to meet their energy needs. People that eat in response to appetite or cravings are responding psychologically and may or may not physically be hungry or be in an energy deficit.
People who eat because of appetite, if they are influenced by food cravings, may be more prone to eat calorie-rich, less-nutrient-dense foods high in refined carbohydrate and/or fat. For those who eat in response to cravings, new information on the role of neurochemicals is becoming available. Hormones are thought to be involved, since food cravings are more common in women, especially during menstruation or pregnancy.
Answer to Question 2
Hunger and satiety are influenced by concentrations of glucose, amino acids, and lipids in the blood. Elevated blood glucose, amino acids, and lipids promote satiety. Decreased levels of glucose, amino acids, and lipids release neurotransmitters that stimulate hunger. The presence of food in the stomach and small intestine can trigger the release of GI hormones (CCK, PYY)the majority of which promote satiety. Ghrelin is one of the few that doesn't promote satiety but appears to signal hunger to the brain.
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