162 lines
8.5 KiB
Plaintext
162 lines
8.5 KiB
Plaintext
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THE FACTS ABOUT FLATULENCE
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by Margaret C. McDonald
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Ever since my hearthmate banned me from eating black bean soup,
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I've been wanting to know the facts about flatulence. Why are
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some, uh, emissions appropriately labeled "silent but deadly"?
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Why do others cause great auditory but not olfactory
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embarrassment? To get answers I turned to Pitt
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gastroenterologist David H. Van Thiel, M.D., who promptly armed
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me with Chapter 19 of the textbook Gastrointestinal Disease,
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titled simply "Intestinal Gas." Between it and the good doctor,
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I am now the office expert on this awkward but interesting
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subject.
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According to chapter authors Michael D. Levitt, M.D., and John H.
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Bond, M.D., "...Medical literature concerning bowel gas is
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relatively long on subjective impressions and short on scientific
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data." Some of the impressions, however (like the one about
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black beans), turn out to have good physiologic explanations.
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Here's what I learned.
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Most of us pass somewhere between 200 and 2,000 ml of gas per day
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(average, about 600 ml) in roughly 13-14 passages. These
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emissions are composed of five gasses: nitrogen (N2), oxygen (O2),
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carbon dioxide (CO2), hydrogen (H2), and methane (CH4). Nitrogen
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usually predominates, followed by variable concentrations of
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carbon dioxide, hydrogen, and methane, and very low levels of
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oxygen. Gas gets into our guts by air swallowing (which accounts
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for very little), production within the bowel and colon (which
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accounts for a lot), and diffusion from the blood. As far as
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those who study these things can figure out, most air that is
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swallowed comes out the way it went in: it is belched or
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"eructed," as the textbook informed me. Most of the nitrogen is
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accounted for by diffusion from blood to bowel; it may give
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flatus some of its bang but little of its bite.
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We are more interested in the gases produced in the bowel's
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interior space or lumen -- the carbon dioxide, hydrogen, and
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methane (all of which are negligible in the atmosphere). These
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gases accumulate when the digestive system's assortment of
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resident bacteria, acting like microscopic gas factories, begin
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the task of digesting our latest meal. It is unclear whether
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carbon dioxide is a direct or indirect product of bacterial
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metabolism, but CO2 can account for up to 50%-60% of the gas in
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flatus, usually in association with hydrogen, which is definitely
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a product of bacterial fermentation. Methane, too, is
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exclusively a bacterial leftover. However, to make the H2 and
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CH4, the bacteria need what Levitt and Bond call "exogenous
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fermentable substrates" -- in English, that's carbohydrate and
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protein. And here's where the science becomes useful in
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answering my questions.
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"Gas is basically produced by foods that have undigestible or
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excess carbohydrates, which are not absorbed when they get to the
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colon, explains Van Thiel. "Beans, for example, have complex
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carbohydrates that are maldigested. And the same holds true for
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mushrooms. Many people don't realize that mushrooms contain a
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unique sugar called raffinose, which humans can't break down.
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Cabbages and onions do the same thing." As a group, vegetarians
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produce more gas than meat-eaters because the intestinal enzymes
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can't digest the cellulose in vegetables' cell walls. However,
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the colon's bacteria relish the stuff. The outcome: When a group
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of young men, in the service of science, feasted on a diet rich
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in pork and beans, their flatus elimination increased from 15 ml
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to 176 ml per hour!
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Great, so this is where the gas comes from. But what about the
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odor, the noise, the frequency -- the embarrassing stuff? The
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amount and odor of flatus, says Van Thiel, are largely accounted
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for by the type of bacteria we have in our guts. Newborn infants
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and germ-free rats have no intestinal bacteria, although the
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infants acquire them almost immediately. "Unless you're
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hermetically sealed, which is essentially what those germ-free
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rats are, you take in bacteria within hours of being delivered;
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and they immediately begin to replicate in the advantageous
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environment of the intestinal system. And it appears as if the
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kind of bacteria you acquire in your neonatal life basically
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persist with you." While the bacteria that make up the
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intestinal flora are generally the same in everyone, "that's like
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saying people are generally the same," says Van Thiel. They do
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the same job but in their own way.
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The reason this is important is that different bacteria digest
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different kinds of carbohydrates. Some make more methane; others
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help hydrogen to combine with sulfur (from other foods or water)
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to make hydrogen sulfide. According to Levitt and Bond, only
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about one-third of us excrete CH4, a capability that, again, seems
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to depend on the bacteria floating around us at birth. There's
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an easy way to determine whether you produce methane or not: if
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you do, your stools will float. This is because CH4 gets trapped
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in the stool, making it less dense than water. Better the
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relatively odorless methane, however, than hydrogen-sulfide,
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which has the unavoidable odor of rotten eggs. "The only notable
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fact about methane is that it burns with a blue flame," says Van
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Thiel, "and that's why crazy college kids who like to, uh, ignite
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their flatus have to be methane producers. And those who make
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more methane are more like flamethrowers than those who don't."
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That answers the odor question, but what about the noise? "What
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makes the loud ones?" I asked the accommodating
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gastroenterologist. The loud ones are basically a function of
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three things, he told me: the volume of gas, the force with which
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it is expelled, and the presence of hemorrhoids or other
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anatomical features that could resonate. "People with large
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hemorrhoids, for example, will have louder flatus than people
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with lax sphincters. Vegetarians, who actually pass a lot of
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gas, frequently have quiet, frequent flatus because they have
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large, bulky stools and looser sphincters. They will be detected
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socially only if it's foul-smelling; whereas, carnivores may have
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less gas but, since they have tighter sphincters and may be more
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constipated, have high drama flatus."
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So what's to be done if we wish to alter our flatulence profiles?
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Paradoxically, studies show that many people who complain of
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discomfort from "too much gas" have essentially the same gas
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volume and composition as normal controls. However, they seem to
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suffer from disordered intestinal motility, with more gas being
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refluxed back into the stomach, as well as an abnormal pain
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response to bowel distention. While anticholinergic agents have
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been prescribed for this problem, their efficacy has not been
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proven. Thus, the path of least resistance is to stop eating the
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offending foods.
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The same advice is good for those who complain of frequent or
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excessive flatus. If much of the excreted gas is composed of
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hydrogen and carbon dioxide, which originate in the body, not the
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air, the problem may be a general malabsorption disorder or
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difficulty with particular foods. A low carbohydrate diet will
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often turn down the flatus volume.
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In addition to the beans, mushrooms, onions, celery, and other
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foods containing complex carbohydrates and undigestible fiber,
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many patients with abdominal complaints also benefit from
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reducing their intake of lactose, the milk sugar in dairy
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products. Most adults lack, to some degree, the enzyme needed to
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digest lactose. "As long as you eat an amount below your
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tolerance threshold, you're asymptomatic," says Van Thiel. "If
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you go above your threshold, then you have gas, cramps, and
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diarrhea." Another culprit may be the sorbitol in diet foods
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like candy, chewing gum, and sugar-free lozenges. Sorbitol is
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another non-digestible carbohydrate; but, because of its form,
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people have a harder time making the association between
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consumption and later discomfort.
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At this point I'm thinking, "Well, I don't want to stop being a
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vegetarian. I like cheese, and onions are a necessity. Maybe I
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can take some medicinal pesticide to kill my intestinal flora and
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recultivate with a less obnoxious set." Wrong, says Van Thiel.
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Even the strongest antibiotics won't seek and destroy all of the
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107 to 1015 bacteria in my distal small intestine and colon; and
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I'm likely to make myself very sick in the process. Thus, after
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my journey into the dark recesses of my bowel, I can only come up
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with one solution: make sure that when I dine on black bean soup
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I dine alone.
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-/Vuarnet International/-
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617/527.oo91
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24oo-16.8k HST/V32bis |