The average healthy Australian bloke passes wind 12 times a day. He releases about half a litre of gas, enough to blow up a small balloon. These days, we know more about farting than ever before. Fearless investigators have collected emissions from all sorts of people on all sorts of diets and documented their findings.
They know what farts are made of, how much they weigh, why some are noisy and what different aromas can mean. They tell us women average only seven a day and report more than half of these are odourless. Men report an odour two thirds of the time.
Everyone has intestinal gas. People swallow air as they eat and drink. Some gulp air when they are nervous. Often this comes back up as a burp, but once the air gets through the stomach, the only way out is the back passage.
Gas is also created in the intestines by bacterial activity; while some is used or re-absorbed, the rest has only one escape route.
When Sydney gastroenterologist Professor Terry Bolin and nutritionist Rosemary Stanton wrote a book on intestinal gas, they were amazed at the response. Their book, Wind Breaks, is now in its third printing and is also being published overseas.
They say the amount of gas a man produces depends on his diet and the kind of bacteria living in his bowel. In a study they conducted, men had farting-range from three to 38 a day. (Volunteers were each given a hand counter to keep in their pockets and click everytime they passed wind. Other researchers insert a small catheter into the rectum to count emissions.)
Some men pass small volumes of gas often and others pass larger volumes less often. Farting frequency depends on the sensitivity of the walls of the rectum. If the walls are sensitive to small amounts of distension, the man will pass small volumes more often than if his rectum tolerates greater distension.
With age, the bowel becomes less elastic and more sensitive to being distended. This means older men often can't hold in gas and so pass wind more frequently, without actually producing more gas.
Dr Michael Levitt, of Minnesot , US, who has published widely on flatus, says farts are made up of five main gases: nitrogen, oxygen, hydrogen, methane and carbon dioxide. All of these are odourless; it is traces of other chemicals that give each fart its unique aroma.
Men who seek medical help for wind are usually concerned about aroma, fearing that a pungent smell indicates bowel disease. But Bolin says odours are usually the result of diet and rarely due to colitis or bowel cancer.
Many protein foods, including meat and eggs, contribute to flatal odour. Some spices and herbs also produce pungent aromas as do onions, garlic and concentrates like shrimp paste. Writing in the latest issue of Australian Doctor, Rosemary Stanton is concerned that fear of flatulence is keeping people from increasing their dietary fibre. There is a correlation between fibre and flatulence, but people who don't eat enough fibre still produce gas.
A Melbourne gastroenterologist, Dr James St John, says there are different types of fibre: people who feel uncomfortable after eating one type should find another that suits them.
Some foods have a reputation for causing flatulence, but there are ways of reducing their gas-producing potential. For example mildly cooked cabbage causes less flatulence than limp, overcooked cabbage. Soaking beans and then discarding the soaking water before cooking reduces their gas potential. Dr Levitt has found (unsoaked) beans increase the average person's output of gas by a factor of 10.
Beans have always suffered bad press. Even Saint Jerome is said to have forbidden his nuns to eat beans, believing that in partibus genitalibus titillationes producunt (they tickle the genitals).