Hunger is the physical sensation and processes that signal our bodies and brains to eat. It can be perceived by low energy levels, rumblings in the stomach, and cravings for food. The cycle of hunger begins with the hormone ghrelin, which communicates with the hypothalamus in the brain, responsible for governing metabolism and regulating the basic body functions such as thirst, sleep, and sex drive. Receiving the message from ghrelin, the hypothalamus triggers the release of neuropeptide Y, which then stimulates appetite. When the brain perceives ghrelin it also signals the hindbrain, which controls the body’s automatic, unconscious process, and the mesolimbic reward center in the midbrain, where feelings of pleasure and satisfaction are processed. In contrast, satiety is the absence of hunger; it is the sensation of feeling full, while appetite is the desire to eat food.
The Biology of Hunger
The hunger cycle is experienced throughout the body. The center of the brain, known as the mesolimbic region, is the area that processes pleasure. The vagus nerve is responsible for signaling the stomach, which secretes digestive acids. The pancreas produces insulin and the liver works to process the sugar and fat and starch coming in. This complex process involves taste, smell, sight, texture, brain chemistry, gut chemistry, metabolism, and psychology.
The change in the levels of the hormone leptin results in the motivation to consume food. Upon eating, adipocytes trigger the release of leptin into the body. Increasing levels of leptin result in a reduction of motivation to eat. After hours of nonconsumption, leptin levels drop significantly, beginning the cycle once again.
Introception and Hunger
Though the body is designed to operate regularly and efficiently, circumstances such as genetic and psychological disorders, over- and underabundance of food, and cultural norms affect how individuals interface with hunger. Most of us learn along the way that even after we have had enough to eat, it can take a while for the brain to get the message. For some, the message of satiety, or fullness, is not received loud and clear. These individuals may have issues with interoception.
Interoception is the perception of the internal state of the body so that an individual recognizes sensations of being full or hungry, hot or cold, itchy or in pain. People who have problems processing sensory information, a condition called sensory processing disorder (SPD), may have impaired interoception and not recognize feelings of hunger or fullness. As a result, they overeat. Further, impaired interoception leads to emotional eating as being aware of the body’s internal state underlies self-awareness and emotional experience.
The peptide cholecystokinin (CCK) increases the feeling of heavy satisfaction, signaling fullness. Glucagon-like peptide-1 (GLP-1) and pancreatic polypeptide (PYY), which are produced in the lower gut, tell the brain the body has had enough and also tell the stomach to stop what it is doing and not move anything further along into the intestines. GLP-1 adjusts blood chemistry, stimulating the pancreas to release more insulin, which soaks up sugars released into the blood by the inrushing food and stores them in the body’s fat deposits.
Thirst occurs when the body needs water. When it does not drink enough water, the body receives mixed signals on hunger. Dehydration causes the brain to believe it needs to eat when the body really needs liquid intake. Hunger is the result because the body incorrectly thinks it needs food for energy. As people get older, they lose their thirst sensation and tend to confuse thirst with hunger. People often mistake hunger for thirst because the adult thirst mechanism is weak. Misdiagnosing the sensation of thirst can easily mislead the body into thinking it needs food when what it is really asking for is water.
Candida overgrowth in the intestines can make the body feel tired and irritable and cause a foggy head and poor concentration. It can also cause intense carbohydrate cravings. Candida is a type of yeast that is naturally present in everyone’s digestive tract; however, if the immune system is weak and digestion is poor, Candida levels can get out of control. Because it is a type of yeast, it needs sugar in order to grow. The overabundance of Candida in the system wants to be fed and its preferred food is sugar. This often results in an individual mistaking such sensations for true hunger.
See also: Brain Anatomy; Interoception; Thirst
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How Stuff Works Science. (n.d.). Stomach hunger—How food cravings work. Retrieved from http://science.howstuffworks.com/innovation/edible-innovations/food-craving1.htm
Kluger, Jeffrey. (2007). The science of appetite. Time. Retrieved from http://content.time.com/time/specials/2007/article/0,28804,1626795_1627112_1626670,00.html