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By Root 932 0

when food enters seems to stimulate the hypothalamus to reduce our level of hunger. When the small intestine releases sugars into the blood, blood sugar concentration increases. When blood sugar levels are high, the pancreas secretes the hormone insulin. For some people, the sight and smell of appealing food can stimulate the secretion of insulin. High levels of insulin generally stimulate hunger. Insulin lowers the blood glucose level by increasing the use of glucose in the tissues, by promoting storage of glucose as glycogen in the liver and muscles, and by promoting formation of fat from glucose. When blood sugar levels are low, insulin release is inhibited and the pancreas secretes the hormone glucagon. Glucagon increases the blood glucose level by stimulating rapid conversion of glycogen into glucose, which is released by the liver and muscles into the bloodstream. Thus, insulin and glucagon work antagonistically through a negative feedback loop to help maintain homeostasis.

Hunger and the Hypothalmus

Neurons in the liver sensitive to glucose in the surrounding fluid send signals to the hypothalamus by way of the vagus nerve. Three parts of the hypothalamus in the brain seem to integrate information about hunger and satisfaction or satiety. The lateral hypothalamus (LH) was originally called the “on” button for hunger. When stimulated, this structure of the brain will start eating behavior, but if it is lesioned or removed, the individual will not eat at all, and will even starve to death. The ventromedial hypothalamus (VMH) was called the satiety center, or “off” button, for hunger. When stimulated, it turns off the urge to eat and when removed, the organism will continue to eat excessively and gain weight rapidly. Recent research indicates a third region of the hypothalamus called the paraventricular nucleus (PVN) also helps regulate eating behavior as a result of stimulation or inhibition by neuro-transmitters. Norepinephrine, GABA, and neuropeptide Y seem to increase the desire for carbohydrates, whereas serotonin seems to decrease the desire for carbohydrates. When the hormone leptin, produced by fat cells, is released into the bloodstream, it acts on receptors in the brain to inhibit release of neuropeptide Y into the PVN, thus inhibiting eating behavior.

Eating and Environmental Factors

Although eating behavior is partially regulated by biological factors, environmental factors such as learned preferences, food-related cues, and stress also influence our desire to eat. We all seem to have some inborn taste preferences for sweet foods, salty foods, and high-fat foods, but learning also influences what we eat. People from different cultures show different patterns of food consumption. Meat and potatoes are consumed in larger quantities in the United States, while rice and fish are the staple foods in Japan. Religious values also influence eating behavior by setting specific rules for the foods we may eat and those we are not permitted to eat. Finally, we tend to learn our food habits from our parents, partly by observational learning and partly by classical conditioning, for example by pairing foods with pleasant social interactions. What, how often, and how much we should eat are expectations we have learned since we were babies.

Obesity

Obesity and the potential for health problems associated with diabetes and hypertension are growing concerns in our population. People of normal weight tend to respond to internal, long-term bodily cues, such as stomach contractions and glucose–insulin levels; while those who are obese pay more attention to the short term, external cues, such as smell, attractiveness of food and whether it is meal time. Stress-induced arousal also stimulates eating behavior in a large proportion of the population.

Aware that obesity often leads to health problems and that millions of people try to lose weight, scientists have studied obesity and weight loss. By studying identical twins who were raised apart, they have found that some people inherit a predisposition to be overweight, while