question: Why is that after being so hungry and not eating, after a while you no longer feel hungry?
comment: Hunger is a signal telling us to eat food. When food isn't available to eat, it's just a distraction, so the body begins to turn it off. We know we still need to eat, but it stops being prevalent in our mind so that we can concentrate on doing the things we need to do to find food.
passages: The physical sensation of hunger is related to contractions of the stomach muscles. These contractions—sometimes called hunger pangs once they become severe—are believed to be triggered by high concentrations of the ghrelin hormone. The hormones Peptide YY and Leptin can have an opposite effect on the appetite, causing the sensation of being full. Ghrelin can be released if blood sugar levels get low—a condition that can result from long periods without eating. Stomach contractions from hunger can be especially severe and painful in children and young adults.
   Section::::Reception.
   During fasting the body switches its main fuel source from carbohydrates to fat tissue fatty acids and amino acids as the main energy sources. The spleen decreases its rate of red blood cell breakdown thus conserving red blood cells. Many intracellular minerals become severely depleted during this period, although serum levels remain normal. Importantly, insulin secretion is suppressed in this fasted state and glucagon secretion is increased.
   Appetite is another sensation experienced with eating; it is the desire to eat food. There are several theories about how the feeling of hunger arises. A healthy, well-nourished individual can survive for weeks without food intake, with claims ranging from three to ten weeks. The sensation of hunger typically manifests after only a few hours without eating and is generally considered to be unpleasant. Satiety occurs between 5 and 20 minutes after eating.
   The set-point theories of hunger and eating are a group of theories developed in the 1940s and 1950s that operate under the assumption that hunger is the result of an energy deficit and that eating is a means by which energy resources are returned to their optimal level, or energy set-point. According to this assumption, a person's energy resources are thought to be at or near their set-point soon after eating, and are thought to decline after that. Once the person's energy levels fall below a certain threshold, the sensation of hunger is experienced, which is the body's way of motivating the person to eat again. The set-point assumption is a negative feedback mechanism. Two popular set-point theories include the glucostatic set-point theory and the lipostatic set-point theory.
   Hunger pangs can be made worse by irregular meals. People who cannot afford to eat more than once a day sometimes refuse one-off additional meals, because if they do not eat at around the same time on the next days, they may suffer extra severe hunger pangs. Older people may feel less violent stomach contractions when they get hungry, but still suffer the secondary effects resulting from low food intake: these include weakness, irritability and decreased concentration. Prolonged lack of adequate nutrition also causes increased susceptibility to disease and reduced ability for the body to self heal.
  
  Section::::World statistics.
   BULLET::::3. Glucostatic hypothesis: The activity of the satiety center in the ventromedial nuclei is probably governed by the glucose utilization in the neurons. It has been postulated that when their glucose utilization is low and consequently when the arteriovenous blood glucose difference across them is low, the activity across the neurons decrease. Under these conditions, the activity of the feeding center is unchecked and the individual feels hungry. Food intake is rapidly increased by intraventricular administration of 2-deoxyglucose therefore decreasing glucose utilization in cells.
   When hunger contractions start to occur in the stomach, they are informally referred to as hunger pangs. Hunger pangs usually do not begin until 12 to 24 hours after the last ingestion of food. A single hunger contraction lasts about 30 seconds, and pangs continue for around 30 to 45 minutes, then hunger subsides for around 30 to 150 minutes. Individual contractions are separated at first, but are almost continuous after a certain amount of time. Emotional states (anger, joy etc.) may inhibit hunger contractions. Levels of hunger are increased by lower blood sugar levels, and are higher in controlled diabetics. They reach their greatest intensity in three to four days and may weaken in the succeeding days, although research suggests that hunger never disappears. Hunger contractions are most intense in young, healthy people who have high degrees of gastrointestinal tonus. Periods between contractions increase with old age. 
   With a typical high-carbohydrate diet, the human body relies on free blood glucose as its primary energy source. The level of blood sugar is tightly regulated; as blood glucose is consumed, the pancreas releases glucagon, a hormone that stimulates the liver to convert stored glycogen into glucose. The glycogen stores are ordinarily replenished after every meal, but if the store is depleted before it can be replenished, the body enters hypoglycemia, and begins the starvation response.
   The term "bulimia" comes from Greek "boulīmia", "ravenous hunger", a compound of βοῦς "bous", "ox" and λιμός, "līmos", "hunger". Literally, the scientific name of the disorder, "bulimia nervosa", translates to "nervous ravenous hunger".
  
  Section::::History.:Before the 20th century.
   Section::::Chart performance.
   Environmental signals and ghrelin are not the only signals that initiate hunger, there are other metabolic signals as well. As time passes between meals, the body starts to take nutrients from long-term reservoirs. When the glucose levels of cells drop (glucoprivation), the body starts to produce the feeling of hunger. The body also stimulates eating by detecting a drop in cellular lipid levels (lipoprivation). Both the brain and the liver monitor the levels of metabolic fuels. The brain checks for glucoprivation on its side of the blood–brain barrier (since glucose is its fuel), while the liver monitors the rest of the body for both lipoprivation and glucoprivation.
   Hunger (motivational state)
  
  Hunger and satiety are sensations. Hunger represents the physiological need to eat food. Satiety is the absence of hunger; it is the sensation of feeling full.
   Section::::Premeal hunger.
  
  Prior to consuming a meal, the body's energy reserves are in reasonable homeostatic balance. However, when a meal is consumed, there is a homeostasis-disturbing influx of fuels into the bloodstream. When the usual mealtime approaches, the body takes steps to soften the impact of the homeostasis-disturbing influx of fuels by releasing insulin into the blood, and lowering the blood glucose levels. It is this lowering of blood glucose levels that causes premeal hunger, and not necessarily an energy deficit.
  
  Section::::Similar conditions.
   Section::::Legacy.
  
  The fast has been the subject of many books and studies taken since 1880. His daily log of weight and physical condition were released to the public for further evaluation. 
  
  Tanner's fame in the coming decades was enough for Mark Twain to mention in passing, "I think that the Dr. Tanners and those others who go forty days without eating do it by resolutely keeping out the desire to eat, in the beginning, and that after a few hours the desire is discouraged and comes no more" in "Following the Equator: A Journey Around the World" in 1897.
   Hunger is also the most commonly used term in social science and policy discussions to describe the condition of people who suffer from a chronic lack of sufficient food and constantly or frequently experience the sensation of hunger, and can lead to malnutrition.
  
  Section::::Hunger pangs.
   Section::::Short-term regulation of hunger and food intake.:Nutrient signals.
  
  Blood levels of glucose, amino acids, and fatty acids provide a constant flow of information to the brain that may be linked to regulating hunger and energy intake. Nutrient signals that indicate fullness, and therefore inhibit hunger include rising blood glucose levels, elevated blood levels of amino acids, and blood concentrations of fatty acids.
  
  Section::::Short-term regulation of hunger and food intake.:Hormone signals.
   Section::::Malnutrition.
  
  Section::::Malnutrition.:Causes.
  
  Malnutrition can be caused by a number of things including inadequate or unbalanced diet, problems with digestion or absorption, or certain medical conditions. Hunger is a main cause of malnutrition because if it is not satisfied then malnutrition is sure to follow. People suffer from hunger because of a lack of food and the nutrients which accompany food in the short term. If hunger proceeds for an extended period of time there is a good chance that it will lead to malnutrition.
   BULLET::::- Stimulate the expression of cocaine and amphetamine regulated transcript (CART).
  
  Though rising blood levels of leptin do promote weight loss to some extent, its main role is to protect the body against weight loss in times of nutritional deprivation. Other factors also have been shown to effect long-term hunger and food intake regulation including insulin.
   BULLET::::- Not eating causes one form of unhealthy snacking. Evelyn Tribole and Elyse Resch claim in their book "Intuitive Eating" that the symptoms of starvation occur when the absence of eating is extended longer than a period of three to six hours. When the body undergoes a period of starvation, metabolism decreases and food cravings increase, causing a binge in eating high-carbohydrate foods. Neuropeptide Y (NPY) is a chemical in the brain produced during periods of starvation that triggers the need for carbohydrates. After a bout of starvation, NPY causes an eating binge of carbohydrates in which one surpasses the daily allowance, causing weight gain. Ingesting carbohydrates causes an increase in serotonin production which cancels the production of NPY. The longer the starvation period, the more intense food cravings become, making it difficult to follow the five characteristics of healthy snacking.
   The process of regaining weight and especially body fat is further promoted by the high metabolic plasticity of skeletal muscle. The "Summermatter Cycle" explains how skeletal muscle persistently reduces energy expenditure during dieting. In addition, food restriction increases physical activity which further supports body weight loss initially. Such weight regain in the form of preferential catch-up-fat is well documented after weight loss due to malnutrition, cancer, septic shock or AIDS and thus constitutes a general phenomenon related to weight loss.
  
  Section::::Effects on health.
   Because patients are being fed intravenously, the subject does not physically eat, resulting in intense hunger pangs (pains). The brain uses signals from the mouth (taste and smell), the stomach and gastrointestinal tract (fullness) and blood (nutrient levels) to determine conscious feelings of hunger. In cases of TPN, the taste, smell and physical fullness requirements are not met, and so the patient experiences hunger, although the body is being fully nourished.
  
  Patients who eat food despite the inability can experience a wide range of complications, such as refeeding syndrome.
  
  Section::::Complications.:Cholecystitis.
   The hormones insulin and cholecystokinin (CCK) are released from the GI tract during food absorption and act to suppress feeling of hunger. CCK is key in suppressing hunger because of its role in inhibiting neuropeptide Y. Glucagon and epinephrine levels rise during fasting and stimulate hunger. Ghrelin, a hormone produced by the stomach, is a hunger stimulant.
  
  Section::::Short-term regulation of hunger and food intake.:Psychological factors.
   Absorptive state
  
  Absorptive state is the period in which the gastrointestinal tract is full and the anabolic processes exceed catabolism. The fuel used for this process is glucose.
  
  Section::::Nutrient processing in the absorptive state.
   Szervánszky decided on the desperate gamble of not eating in order to starve himself into a state of weakness. Over the course of a few weeks he ate less and less. His physical state rapidly deteriorated to the extent that he weighed only thirty-eight kilos. His plan worked and he was released as of no practical use as a worker.
  
  Section::::Life and career.:After the war.
  