Most of these gases are either swallowed inadvertently when food is eaten or released from the food as it is digested. What makes this remarkable to most people is not just that these gases are so common but that they are also utterly odorless. For flatus to attain its singular bouquet, it must rely on the remaining 1 percent of the gas that makes it up–a percent composed of very different stuff, which comes from a very different source. Like all complex organisms, the human body is home to millions of microorganisms that live in our hair, pores, and even our internal organs.
The part of the body that is apparently zoned for the most residential development–at least by house-hunting one-celled organisms without much of an eye for resale values–is the digestive tract. Among the better known microbes that receive their E-mail and E! channel in your intestines is the prolific E. coli. Among the lesser known are Klebsiella and Clostridium. All these organisms live for the most part in the colon, where they attack and consume undigested food and in turn generate their own waste products. In the case of microorganisms, waste usually means gas, and in the case of these microorganisms, that gas can be pretty ripe stuff–usually molecules containing sulfur, such as dimethyl sulfide and methanethiol. When these waste products build up to a sufficient level, they are released with the rest of the gas in the bowels, announcing their presence–and too often yours–to the world.
The odoriferous gases present in flatus are present in extremely small concentrations, Levitt says. It is a testament both to the pungency of the gases and to the sensitivity of the nose that we can detect them so readily. Of course, not all episodes of flatulence carry an olfactory price tag. Some people, it seems, can release all the intestinal gas they want with no one the wiser, while other people seem to be unable to enter a room without first having to file an environmental impact statement. While it’s tempting to conclude that individual quirks of individual metabolisms account for these differences, the answer usually has less to do with our bodies than with what we put into them–particularly when what we put into them are carbohydrates. Nutritionists have long known that while there are many kinds of carbohydrates present in food, Levitt says, not all of them are digestible. Generally it is only the simplest carbohydrates, made up of the simplest sugars, that we’re able to process.
Some complex carbohydrates– those made up of three or four sugar molecules–can’t be broken down by normal metabolism. When these get into the digestive tract, they are simply passed along to the colon, where the intestinal flora get hold of them. Among the foods with the fewest complex carbohydrates and thus the fewest flatulent consequences are meat, fish, grapes, berries, potato chips, nuts, and eggs–the so-called normoflatugenic foods. Further up the gaseousness scale are pastries, potatoes, citrus fruits, apples, and breads, all of which contain some complex sugars, and thus some potential for flatulent fallout. At the top of the explosiveness list are the Fat Man and Little Boy of our diets–those foods that are practically nothing but complex sugars. Among these most eruptive edibles are beans, carrots, raisins, bananas, onions, milk, and milk products. When Levitt began treating his grievously gassy patient, it was these well-nigh radioactive consumables that first drew his attention. In his initial journal paper, as well as in a subsequent paper entitled Follow-up of a Flatulent Patient (itself later followed up by Flatulent Patient: The Musical!), Levitt described the painstaking process by which the patient altered his diet to determine which foods were responsible for his distress.
