Breaking Wind

I dedicate the following newspaper article to some of my students and teachers, some female tennis players, Coca Cola and Singapore Power for their immortal commitment, dedication and contribution to our gassy society.

The Straits Times MAY 29, 2004 Sat

Breaking wind: clearing the (foul)air

Do you have a burning science question? In our weekly series, we get experts to help unravel the mysteries of the universe. Send your questions to stlocal@sph.com.sg

I would like to know why we break wind? And why do some people do it loudly and others silently?

THE technical name for flatulence is 'flatus', or 'rectal gas'. It is actually intestinal gas released via the rectum, referred to also as 'fart' or 'cutting the cheese'.
Gas gets into our digestive system in various ways: by swallowing air, which accounts for very little; production within the intestinal tract, which accounts for a lot; and diffusion from the blood.
The gas that is diffused from the blood is mainly nitrogen and constitutes part of the rectal gas.
Gas is usually removed from our body via belching and breaking wind.
Each time a person swallows food or liquid, he swallows some air. The more frequently a person swallows, the greater the amount of air entering the stomach.
Most air that is swallowed comes out the way it went in. Hence, everyone belches occasionally, often after eating. Since the stomach does not produce air or gas on its own, belching is simply the release of swallowed air from the stomach.
To find out more about flatulence, we have to understand how our intestinal tract works.
Solid food and liquid travel down our throat to the stomach via the oesophagus or gullet.
In the stomach, food is churned into small pieces, partially digested, and then emptied into the small intestine.
How quickly the stomach empties varies, but generally, it happens in one to two hours after eating. The small intestine gently contracts, moving these food fragments down the intestinal tract.
Digestion and absorption of the food substances continue in the small intestine. Here, amino acids, glucose, minerals, vitamins and other nutrients are absorbed.
The indigestible liquid waste then reaches the large intestine, or the colon. Here, much of its water is reabsorbed, leaving behind the more solid stool.
Flatus is gas produced as a result of bacterial activity in the colon, which has hundreds of different bacteria growing in it. These bacteria live peacefully there and provide certain positive health benefits to the body.
In other words, they are harmless and cause no problems. They rely on the indigestible food we eat for their own nutrition.
Certain foods are more likely to cause certain types of bacteria to thrive. Some of these bacteria are called 'gas formers'.
Gas-forming bacteria generally feed on three nutrients: carbohydrates, fats and proteins. Carbohydrates produce the most gas.
If the amount of carbohydrates is reduced or eliminated from the diet, rectal gas or flatus can usually be reduced significantly.
An individual's response to certain foods is also a factor in producing rectal gas. Two people eating the same amount of the same carbohydrate can produce different amounts of rectal gas.
On average, we have about 14 'toots' per day. How often they happen do not seem to be determined by gender, age or the ability of an individual's colonic flora.
What about the noise? What makes some people break wind loudly?
Contrary to popular belief, the sound is not due to the flapping of the butt!
It is produced by the vibrations of the anal opening.
The loud toots are basically a result of three things - the volume of gas, the force and velocity with which it is expelled, and the tightness of the anus' sphincter muscles.
The presence of haemorrhoids and other anatomical features that could resonate also affects the sound.
People with large haemorrhoids, for example, will sound off louder than people with lax anal sphincter muscles.
Vegetarians, who actually pass out a lot of gas, would be quieter because they have large, bulky stool and looser sphincters. Their breaking wind will be detected socially only if what they let off is foul-smelling.
Carnivores may have less gas but, since they have tighter anal sphincter muscles and may be more constipated, their toots could be high drama!
Studies have shown that the actions related to flatulence - contractions of the colon, together with a rise in pressure in the rectum and early relaxation of the anal sphincter - are similar to those observed after swallowing, believe it or not!

Assistant Professor Diana Ang
National Institute of Education
Nanyang Technological University