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Burping is generally caused by swallowing air when eating or drinking and subsequently expelling it, so in this case the expelled gas is mainly a mixture of nitrogen and oxygen. Burps can also be caused by drinking carbonated beverages, such as beer, soft drinks, energy drinks, and wine in which case the expelled gas is primarily carbon dioxide from the drink itself. Common diabetes drugs metformin and Byetta can cause burping, especially at higher doses. This often resolves in a few weeks. Burping combined with other symptoms such as dyspepsia, nausea and heartburn may be a sign of an ulcer or hiatal hernia, and should be reviewed by a physician. Other causes of burping include: food allergy, gallbladder problems, acid reflux disease, H. pylori, and gastritis.
In microgravity environments burping is normally associated with regurgitation. The valve at the top of the stomach (the gastroesophageal junction) does not produce a tight seal, and in the absence of gravity, the stomach contents tend to float near this loose seal, making them likely to come up along with the expelled air.
Inability to burp is uncommon, and chest pain caused by dysfunction of the belch reflex is rare.
Babies are particularly subject to accumulation of gas in the stomach while feeding, and this can cause considerable discomfort and agitation unless the child is burped. The act of burping an infant involves placing the child in a position conducive to gas expulsion (for example holding the infant up to the adult's shoulder, with the infant's stomach resting on the adult's chest) and then lightly patting the lower back so that the child burps. Because burping can cause vomiting in infants, a "burp cloth" or "burp pad" is sometimes employed on the shoulder to protect the adult's clothing.
Some cultures, notably Chinese and Indian, regard burping as acceptable in certain situations. In Japan, burping during a meal is considered bad manners. In others, particularly Western cultures, such as North American and European cultures, burping is also deemed socially inappropriate. In Middle Eastern countries it is not acceptable to burp out loud, and one should silence one's burp, or at least pretend to do so.
It is possible to voluntarily induce burping through swallowing air and then expelling it, and by manipulation of the vocal tract produce burped speech.
While this is often employed as a means of entertainment or competition, it can also act as an alternative means of vocalisation for people who have undergone a laryngectomy, with the burp replacing laryngeal phonation. This is known as esophageal speech.
In other animals
Many other mammals, such as cows, dogs, and sheep also burp. In the case of ruminants, much of the gas (wind) expelled is produced as a byproduct of the animal's digestive process. These gasses notably include a large volume of methane, produced exclusively by a narrow cohort of methanogenic archaea in the animal's gut; Escherichia coli (E. coli) and other bacteria lack the enzymes and cofactors required for methane production. Cows are thought to emit an average of 542 litres (if located in a barn) and 600 litres (if in a field) of methane per day through burping and exhalation, making commercially farmed cow a major[quantify] contributor to the greenhouse effect. 95% of this gas (wind) is emitted through burping. This has led scientists at the Commonwealth Scientific and Industrial Research Organisation of Perth, Australia, to develop an anti-methanogen vaccine to minimize methane in cow burps.
One reason why cows burp so much is that they are often fed foods that their digestive systems cannot fully process, such as corn and soy. Some farmers have reduced burping in their cows by feeding them alfalfa and flaxseed, which are closer to the grasses that they had eaten in the wild before they were domesticated.
In some animals, a failure to burp successfully can be fatal. This is particularly common among domesticated ruminants that are allowed to gorge themselves on very rich[clarification needed] spring clover or alfalfa. The condition, known as bloat, is a high pressure buildup of gas in the stomach(s) and requires immediate treatment to expel the gas, usually the insertion of a flexible rubber hose down the esophagus, or in extreme cases the lancing of the animal's side with a trochar and cannula.
There is no documented evidence that birds burp, though ornithologists believe that there is nothing which physiologically prevents them from doing so. However, since the microbiota of birds doesn't include the same set of gas-producing bacteria that mammals have to aid in digestion, gas rarely builds up in the gastrointestinal tracts of birds.
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