Flatulence

Overview
Flatulence is the presence of a mixture of gases known as flatus in the digestive tract of mammals expelled from the rectum. It is more commonly known as 'farting', 'passing gas', or 'passing wind' (UK).

Explanation
Flatus is expelled under pressure through the anus, whereby, as a result of the voluntary or involuntary tensing of the anal sphincter, the rapid evacuation of gases from the lower intestine occurs. Depending upon the relative state of the sphincter (relaxed/tense) and the positions of the buttocks, this often results in an audible crackling or trumpeting sound, but gas can also be passed quietly. The olfactory components of flatulence include skatole, indole, and sulfurous compounds. The non-odorous gases are mainly nitrogen (ingested), carbon dioxide (produced by aerobic microbes or ingested), and hydrogen (produced by some microbes and consumed by others), as well as lesser amounts of oxygen (ingested) and methane (produced by anaerobic microbes). Odors result from trace amounts of other components (often containing sulfur compounds, see below).

Composition of flatus gases
Nitrogen is the primary gas released. Carbon dioxide is often present, especially in persons who drink carbonated beverages in quantity. Methane and hydrogen, lesser components, are flammable, and so flatus is susceptible to catching fire. Not all humans produce flatus that contains methane. For example, in one study of the feces of nine adults, only five of the samples contained bacteria capable of producing methane. Similar results are found in samples of gas obtained from within the rectum.

The gas released during a flatus event frequently has a foul odor which mainly results from low molecular weight fatty acids such as butyric acid (rancid butter smell) and reduced sulfur compounds such as hydrogen sulfide (rotten egg smell) and carbonyl sulfide that are the result of protein breakdown. The incidence of odoriferous compounds in flatus increases from herbivores, such as cattle, through omnivores to carnivorous species, such as cats or dogs. Flatulence odor can also be caused by the presence of large numbers of microflora bacteria and/or the presence of feces in the rectum.

The major components of the flatus by percentage are:


 * Nitrogen - 20% - 90%
 * Hydrogen - 0% - 50%
 * Carbon Dioxide - 10% - 30%
 * Oxygen - 0% - 10%
 * Methane - 0% - 10%

Mechanism of action
The noises commonly associated with flatulence are caused by the vibration of the anal sphincter, and not by the buttocks. The sound varies depending on the tightness of the sphincter muscle and velocity of the gas being propelled, as well as other factors such as water and body fat. The auditory pitch (sound) of the flatulence outburst can also be affected by the anal embouchure. Among humans, farting sometimes happens accidentally, such as incidentally to coughing or sneezing; on other occasions, farting can be voluntarily elicited by tensing the rectum or "bearing down" and subsequently releasing the anal sphincter. Humans are also known to flatulate during sleep, largely due to the relaxed state of body muscles, which results in the average person flatulating about 10-20 times through any given night.

Flatus is brought to the rectum via peristalsis, which also causes feces to descend from the large intestine, and may cause a similar feeling of urgency and discomfort. Nerve endings in the rectum usually enable individuals to distinguish between flatus and feces, although loose stool can confuse the individual, occasionally resulting in accidental defecation.

Causes
Intestinal gas is composed of varying quantities of exogenous sources (air that is ingested through the nose and mouth) and endogenous sources (gas produced within the digestive tract). The exogenous gases are swallowed (aerophagia) when eating or drinking or increased swallowing during times of excessive salivation (as might occur when nauseated or as the result of gastroesophageal reflux disease). The endogenous gases are produced either as a by-product of digesting certain types of food, or of incomplete digestion. Anything that causes food to be incompletely digested by the stomach and/or small intestine may cause flatulence when the material arrives in the large intestine due to fermentation by yeast or bacteria normally or abnormally present in the gastrointestinal tract.

Flatulence-producing foods are typically high in certain polysaccharides (especially oligosaccharides such as inulin) and include beans, lentils, dairy products, onions, garlic, scallions, leeks, radishes, sweet potatoes, cashews, Jerusalem artichokes, oats, wheat, yeast in breads, and other vegetables. Cauliflower, Broccoli, cabbage and other cruciferous vegetables that belong to the Brassica family are commonly reputed to not only increase flatulence, but to increase the pungency of the flatus. In beans, endogenous gases seem to arise from complex oligosaccharide (carbohydrates) that are particularly resistant to digestion by mammals, but which are readily digestible by microorganisms that inhabit the digestive tract. These oligosaccharides pass through the upper intestine largely unchanged, and when they reach the lower intestine, bacteria feed on them, producing copious amounts of flatus. In the case of those with lactose intolerance, intestinal bacteria feeding on lactose can give rise to excessive gas production when milk or lactose-containing substances have been consumed.

Interest in the causes of flatulence was spurred by high-altitude flight and the space program; the low atmospheric pressure, confined conditions, and stresses peculiar to those endeavours were cause for concern.

Dietary
Certain spices have been reported to counteract the production of intestinal gas, most notably cumin, coriander, caraway and the closely related ajwain, turmeric, asafoetida (hing), epazote, and kombu kelp (a Japanese seaweed). Most starches, including potatoes, corn, noodles, and wheat, produce gas as they are broken down in the large intestine. Rice is the only starch that does not cause gas. The amount of water-soluble oligosaccharide in beans that may contribute to production of intestinal gas is reputed to be reduced by a long period of soaking followed by boiling, but at a cost of also leaching out other water-soluble nutrients. Also, intestinal gas can be reduced by fermenting the beans, and making them less gas-inducing, and/or by cooking them in the liquor from a previous batch. Lactobacillus casei and Lactobacillus plantarum have recently been hypothesized as being responsible for this effect. Some legumes also stand up to prolonged cooking, which can help break down the oligosaccharides into simple sugars. Fermentation also breaks down oligosaccharides, which is why fermented bean products such as miso and tofu are less likely to produce as much intestinal gas.

Probiotics (yogurt, kefir, etc.) are reputed to reduce flatulence when used to restore balance to the normal intestinal flora. Yogurt contains Lactobacillus acidophilus which may be useful in reducing flatulence. L. acidophilus may make the intestines more acidic, thus maintaining the natural balance of fermentation processes. L. acidophilus is available in supplements (non-dairy is reputedly best. Prebiotics, which generally are non-digestible oligosaccharides, such as fructooligosaccharide, generally increase flatulence in a similar way as described for lactose intolerance.

Medicinal activated charcoal tablets have also been reported as effective in reducing both odor and quantity of flatus when taken immediately before food that is likely to cause flatulence later.

Pharmacological
Digestive enzyme supplements may significantly reduce the amount of flatulence caused by some components of foods not being digested by the body and thereby promoting the action of microbes in the small and large intestines. It has been suggested that alpha-galactosidase enzymes, which can digest certain complex sugars, are effective in reducing the volume and frequency of flatus. The enzymes alpha-galactosidase (brands Beano, Bean-zyme), lactase (brand Lactaid), amylase, lipase, protease, cellulase, glucoamylase, invertase, malt diastase, pectinase, and bromelain are available, either individually or in combination blends, in commercial products.

The antibiotic rifaximin, often used to treat diarrhea caused by the microorganism E. coli, may reduce both the production of intestinal gas and the frequency of flatus events.

While not affecting the production of the gases themselves, surfactants (agents which lower surface tension) can reduce the disagreeable sensations associated with flatulence, by aiding the dissolution of the gases into liquid and solid fecal matter. Preparations containing simethicone reportedly operate by promoting the coalescence of smaller bubbles into larger ones more easily passed from the body, either by burping or flatulence. Such preparations do not decrease the total amount of gas generated in or passed from the colon, but make the bubbles larger and thereby allowing them to be passed more easily.

Often it may be helpful to ingest small quantities of acidic liquids with meals, such as lemon juice or vinegar, to stimulate the production of gastric hydrochloric acid. In turn, acid ingestion may increase normal gastric enzyme and acid production, facilitating normal digestion and perhaps limiting intestinal gas production. Ingestion of bromelain- or papain-containing supplements (such as pineapple or papaya, respectively, may be helpful.

Odor from flatulence, caused by the intestinal bacteria called microflora in the bowel, can be treated by taking bismuth subgallate (brand Devrom). Bismuth subgallate is commonly used by individuals who have had ostomy surgery, bariatric surgery, fecal incontinence and irritable bowel syndrome.

Post-Release
In 1998, Chester "Buck" Weimer of Pueblo, Colorado, USA received a patent for the first undergarment that contained a replaceable charcoal filter. The undergarments are air-tight and provide a pocketed escape hole in which a charcoal filter can be inserted.

A similar product was released in 2002, but rather than an entire undergarment, consumers are able to purchase an insert similar to a pantiliner that contains activated charcoal. The inventors, Myra and Brian Conant of Milihani, Hawaii, USA still claim on their website to have discovered the undergarment product in 2002 (8 years after Chester Weimer filed for a patent for his product), but states that their tests "concluded" that they should release an insert instead.

Health effects
As a normal body function, the action of flatulence is an important signal of normal bowel activity and hence is often documented by nursing staff following surgical or other treatment of patients. However, symptoms of excessive flatulence can indicate the presence of irritable bowel syndrome or some other organic disease. In particular, the sudden occurrence of excessive flatulence together with the onset of new symptoms provide reason for seeking further medical examination.

Flatulence is not poisonous; it is a natural component of various intestinal contents. However, discomfort may develop from the build-up of gas pressure. In theory, pathological distension of the bowel, leading to constipation, could result if a person holds in flatus.

Not all flatus is released from the body via the anus. When the partial pressure of any gas component of the intestinal lumen is higher than its partial pressure in the blood, that component enters into the bloodstream of the intestinal wall by the process of diffusion. As the blood passes through the lungs this gas can diffuse back out of the blood and be exhaled. If a person holds in flatus during daytime, it will often be released during sleep when the body is relaxed. Some flatus can become trapped within the feces during its compaction and will exit the body, still contained within the fecal matter, during the process of defecation.

Environmental impact
Flatulence is often blamed as a significant source of greenhouse gases owing to the erroneous belief that the methane released by livestock is in the flatus. While livestock account for around 20% of global methane emissions, 90 to 95% of that is released by exhaling or burping. This means only 1–2% of global methane emissions come from livestock flatus.

Social context
In many cultures, human flatulence in public is regarded as embarrassing and repulsive, even to the point of being a taboo subject. People will often strain to hold in the passing of gas when in polite company, or position themselves to conceal the noise and smell. In other cultures it may be no more embarrassing than coughing.

Flatulence is a potential source of humor, either due to the foul smell or the sounds produced. Some find humour in flatulence ignition, which is possible due to the presence of flammable gases such as hydrogen and methane, though the process can result in burn injuries to the rectum, anus and surrounding buttocks.

While the act of farting is generally considered to be an unfortunate occurrence in public settings, a flatus may, in casual circumstances, be used as either a humorous supplement to a joke, or as a comic activity in and of itself.

The History of Farting, by Benjamin Bart, is a collection of assorted limericks, facts, and blurbs on farting, while Who Cut the Cheese: A Cultural History of the Fart, by Jim Dawson, gives a more complete cultural discussion of the historical and social significance of farting.