How come: Flatulence, or how to clear a room
BY KATHY WOLLARD | Special to Newsday
February 18, 2008
From today's Chicago Tribune:
(note comments at bottom of article)
How and why does the human body produce wind? What causes the odor of gas? asks Nayna Kumari, via e-mail.
Whether we call it breaking wind, passing gas or something more impolite, everyone experiences flatulence. And it's not just we humans; creatures from farm animals to household pets get gassy, too. (Looking pointedly at the dog, in fact, is a favorite way to dodge flatulence blame in a small room.)
Gastroenterologists say most people pass gas about 10 to 20 times a day. And just as in the old saying "Horses sweat; men perspire; women glow," females seem favored in the flatulence department, too. Because women's bodies are usually smaller than men's, they may pass less gas. According to Dr. Michael Levitt, a gastroenterologist and flatulence expert in Minneapolis, if the average man's gassy output amounts to about five cups a day, the average woman's might be three.
Intestinal gas builds up when food isn't completely digested. Food that is digested only partially in its trip through the stomach and the 20-plus feet of the small intestine passes into the large intestine (colon). The colon is where last-chance digestion goes on, as bacteria work on breaking down leftover food before it leaves the body as waste.
Bacteria quickly multiply as they get to work on fiber and other undigested carbohydrates. As they break down, or "ferment" food, gases are a byproduct. It's the same story when yeast fungi break down sugars in bread dough; the carbon dioxide they release makes the dough swell and expand. And just as dough rises, so do our doughy abdomens distend a bit from trapped gases. Some of the gas is absorbed into the body and bloodstream. And some is (embarrassingly) expelled into the air.
Some foods make us more gassy than others. Beans, beans, the musical fruit ... er, legume? The more you eat, the more you clear the room?
According to Levitt, beans top the gas and bloating list for most people. Besides lots of fiber, beans contain complex sugars that aren't broken down until they reach the colon. Other foods high on the flatulence charts include cruciferous vegetables such as cabbage and broccoli, as well as "sugar alcohols" like sorbitol.
Suddenly upping the fiber in your diet also can cause bloating. If your body doesn't produce the enzyme that breaks down lactose (milk sugar), dairy foods can be the culprit. And then there's plain old swallowed air.
The main ingredients in passed gas - nitrogen, oxygen, carbon dioxide, hydrogen and methane - are odorless. That's why natural gas suppliers add smelly sulfurous compounds to the mostly-methane gas piped to your stove or furnace. The rotten-egg odor can alert you to a dangerous gas leak. Likewise, what gives intestinal gas its often unpleasant odor are traces of sulfur compounds, plus pungent chemicals like indole and skatole.
Intestinal bacteria produce these smelly compounds as they work on fermenting food. (So do between-teeth bacteria, contributing to the noxious odor of bad breath.) But in a twist, tiny traces of indole and skatole also help create the flowery fragrance of orange blossoms, as well as many perfumes.