Natural gas

Clearing the air...

This article comes with a health warning attached because it is concerned with the embarrassing subject of farting and belching. If you are eating and drinking as you read this article you might like to postpone that activity until after you have finished reading. Alternatively you might like to continue eating or drinking and defer reading this until later. This article will not trawl the depths of puerile humour on this subject. It is a serious attempt to clear the air and that is the sole pun contained within this article.

The flatus or gas within our digestive system comes from a variety of sources. Some of it may be swallowed down into the stomach especially if we eat or drink too quickly. Bacteria in the large intestine or colon also produce some of the intestinal gas and some of it is transferred from the blood stream into the gut in a process known as diffusion. Most of the swallowed gas leaves the way it came in by belching and this action occurs when the gas over inflates the stomach. Further down the gut bacteria that colonise the large intestine produce most of the gas contained therein and most of it is released through the anus. A smaller portion of this gas diffuses into the bloodstream and is exhaled when we breathe.

Five gases

The gas emissions mainly consist of five gases: nitrogen, oxygen, carbon dioxide, hydrogen and methane. Some of the nitrogen gets into the gut by diffusion from the blood and is the predominant gas in the gut, followed by variable concentrations of carbon dioxide, hydrogen, methane and very low levels of oxygen. There is a sixth gas present but this is contained in tiny trace amounts. I refer to sulphur, which is contained in meat, eggs and cauliflower and it contributes significantly to the smell of a fart. Its impact on smell is disproportionate to its actual volume

We cannot avoid swallowing air when we swallow our food or drink but we can reduce the amount being swallowed by chewing more slowly and not bolting our food down. Additional amounts of gas are produced in the stomach through the process of digestion. Saliva reacts with the hydrochloric acid in the stomach to produce carbon dioxide. Chewing gum can contribute to carbon dioxide production because of the continuous production of saliva associated with such chewing. Therefore if you have a problem with belching you might consider reducing your consumption of chewing gum especially if you happen to chew a lot of it. Further along the gut additional amounts of carbon dioxide are produced in the duodenum where the gastric and pancreatic juices mix.

Bacterial action

Bacteria in the colon account for most of the gas emitted in a fart. The gas is produced by bacterial action leading to the fermentation of foods that have not been digested or absorbed by the time they get to the colon. The type of bacteria present in the colon can influence the amount and odour of flatus. Newborn infants have no intestinal bacteria although they acquire them very quickly after birth. It would appear that the type of bacteria we acquire in neonatal life persist throughout childhood and into adulthood. Different bacteria digest different kinds of carbohydrates. Some produce more methane whereas others help to combine hydrogen with sulphur to make hydrogen sulphide. This is the chemical that produces the odour of rotten eggs. Methane is the gas that produces the flame-thrower effect most beloved by very juvenile university students and coincidentally methane production from cattle is now being blamed as a significant contributor to global warming.

Beans and peas are famous for their gas produce effects. This is because they contain large amounts of complex carbohydrate, which pass into the colon largely unabsorbed. However, beans and peas are not the only potential culprits. Troublesome foods may include vegetables of the cabbage family such as broccoli, Brussels sprouts, cabbage and cauliflower. You can add to that list asparagus, cucumber, onions, turnip, peppers, garlic, melons, spicy foods and cheeses such as Roquefort, Brie and other strong cheeses.

Certain types of seafood such as prawns, crab and salmon may also contribute to difficulties with flatulence. Mushrooms can also create difficulty because they contain a particular sugar called raffinose, which humans cannot digest. As a group, vegetarians produce more gas than meat eaters because of the higher level of non-digestible foodstuffs in their diet. It is also appropriate to mention that if you are increasing the amount of fibre in your diet you should do so by degrees because the gut needs to adjust gradually to the increased fibre load.

Weight loss

People who are trying to lose weight also need to be aware that some foods that are advertised as slimming aids also create extra flatus. Some slimming chocolate contains sorbitol and most of this substance is not absorbed from the gut, which is the very reason why it is marketed for people who want to lose weight. This material reaches the colon in undigested form and is subjected to bacterial action, which again leads to fermentation and gas production.

Common sense tells us that many people belch because they eat too much. When we overeat the bubble of air that normally floats on top of the liquid contents of the stomach becomes pressurised because the stomach is too full. In order to relieve the raised pressure some of that air bubble is released in the form of a belch. Tight fitting clothing can also cause pressure effects on the abdomen and cause trapping of flatus. In that case it might be worth avoiding tight belts, corsets and other figure maintaining clothing. It really could ruin your night and your partners if you had the figure of a Goddess but could not stop breaking wind!

Farting and belching rarely indicate the presence of underlying disease when no other symptoms are present. However, excessive flatus can occur as a result of a variety of medical conditions. For example people suffering from lactose intolerance lack an enzyme in the gut that breaks down lactose, which is the principal sugar found in dairy products. The non-digested and consequently unabsorbed lactose then travels on to the colon where it is subjected to bacterial action. Similarly people suffering from diseases of the pancreas may not absorb certain nutrients, which again travel on to the colon. In general terms people that suffer from various forms of malabsorption syndrome tend to have excessive amounts of flatus and can produce stools with a very strong odour.

Natural gas

Some experts believe that our attempts to avoid farting are an unnatural result of our enclosed lifestyles and that when our ancestors lived in the great outdoors farting was not a problem. It is even suggested by some that holding on may be a factor in the building up of pressure in the gut that can be a contributory factor in the development of diverticular disease.

Finally I would like to stress that I do not advocate that people who fart or belch too much should adopt an extreme approach and totally exclude the various gas producing foods that I have listed. Most people do not get sufficient fibre in their diets and most of us should include more fruit, cereals and vegetables in our daily diet. However, if you consume an excessive amount of any of the foods I have listed it would be reasonable to reduce your intake of that particular food and monitor your response.

* Dr Leonard Condren is the medical editor of

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