A Whiff at What Causes Flatulence

Flatus is the name given to the combination of gases that are expelled at high-speed through the rectum. There are two main causes:

Ingested air - exogenous source of air coming through the mouth and nose. The air is also swallowed as we eat and drink. Consequently the primary gas release during flatulence is nitrogen, which is the main constituent of air.

Food - for food to be useful to our body it has to be absorbed into the bloodstream and usually this occurs through the lining of the stomach and small intestine. However, many foods contain long chain sugar molecules known as carbohydrates which cannot be absorbed. But what our bodies can't handle microbes will, and so carbohydrates pass into the colon for further processing. Here hundreds of different types of bacteria start to break them down. One of the results of this bacterial digestion is the gas that's given off as a by-product and released as flatulence.

Some of the foods which contain a large amount of indigestible carbohydrates are beans, pulses, raisins, broccoli, leeks, sweet potatoes, and turnips. Generally speaking, the more indigestible carbohydrates that are in a food stuff then the bigger the contribution to flatulence.

Flatulence is made up of odourless gases - nitrogen, oxygen, hydrogen, carbon dioxide, and sometimes methane. The nose-turning unpleasant whiff comes from bacteria that release gases consisting of sulphur, and nitrogen compounds such as skatole and indole. Examples of bacteria that cause flatulence include:

Bifidobacteria bifidus - friendly (probiotic), non-motile bacteria inhabiting the gastrointestinal tract and cause the production of hydrogen sulphide and sulfur dioxide

Bifidobacteria bulgaricus - friendly (probiotic), non-motile bacteria inhabiting the gastrointestinal tract and cause the production of hydrogen sulphide and sulfur dioxide

Lactobacillus acidophilus - ferment sugars into lactic acid and inhabit the gastrointestinal tract. Some strains have friendly characteristics.

Methanobrevibacter smithii - the dominant archaeon (single-celled microorganism) in the gastrointestinal tract; it causes the production of methane.

 You can blame it on the person next to you, the cat, or even grandma, but no matter who you are you will pass wind at least 10-14 times every day.

The whiff is variable depending on the type of food we eat, the bacteria in our gut and how much air we have swallowed.

If you hold in a fart you are only delaying the inevitable; it will come out at some point, although some of the gases maybe absorbed into the bloodstream.

Farts are flammable because they contain flammable gases - methane (sometimes) and hydrogen.

On average, a person will release about half a litre of flatus a day.

by Tilo Hauke - released under Creative Commons Attribution ShareAlike 2.5