Intestinal Gas and Diving (Flatus)

Diving with intestinal gas can be an experience that most of us would rather not even think of–much less have to deal with.The gas has to conform to Boyle’s law and can cause extreme discomfort in ascending from depth–particularly if it has become trapped or increased in amount from whatever source.

Gas is the production of digestion, and most of us pass (fart, poot, bubble) somewhere between 200 and 2,000 ml of gas per day (average, about 600 ml) in roughly 13-14 passages. There was a paper in 1976 reporting a patient who passed gas 34 times in one twenty-four hour period. These emissions are composed of five gases: nitrogen (N2), oxygen (O2), carbon dioxide (CO2), hydrogen (H2), and methane (CH4). Nitrogen usually predominates, followed by variable concentrations of carbon dioxide, hydrogen, and methane, and very low levels of oxygen.
Gas also gets into our guts by air swallowing (which accounts for very little in the lower portions), production within the bowel and colon (which accounts for a lot), and diffusion from the blood. Most air that is swallowed comes out the way it went in: it is belched or “eructed,” and in divers this can distend the stomach to the bursting point. Most of the nitrogen is accounted for by diffusion from blood to bowel; it may give flatus some of its bang but little of its bite. I’m not aware that this N2 has any relationship decompression sickness.

The function of the digestive process is to break the presented food into small essential nutrients, which then pass through the bowel wall (absorption) into the blood stream for transportation (distribution) to the various locations where they are used for either the work (metabolism) or construction/repair (anabolism) of the body. Nutrients not needed immediately are stored as fat or glycogen for future use.

Bacteria in the bowel account for 50- 60 % of the gas in flatus –most from the breakdown of carbohydrates, with the production of CO2, hydrogen and methane, often a function of fermentation.

Gas is basically produced by foods that have undigestible or excess carbohydrates, which are not absorbed when they get to the colon. Beans, for example, have complex carbohydrates that are maldigested. And the same holds true for mushrooms, cabbages and onions. Many people don’t realize that mushrooms contain a unique sugar called raffinose, which humans can’t break down. As a group, vegetarians produce more gas than meat-eaters because the intestinal enzymes can’t digest the cellulose in vegetables’ cell walls. However, this is where the colon’s bacteria come in: the outcome being a marked increase in gas production. “Beano”is the answer to this problem for those of us that have these “carbohydrate eating” bacteria. A few Beano drops will close down this flatus-factory and tablets exist for the more self-conscious restaurant diner.
The amount and odor of flatus are largely accounted for by the type of bacteria we have in our guts. Newborn infants and germ-free rats have no intestinal bacteria, although the infants acquire them almost immediately. And it appears as if the kind of bacteria you acquire in your neonatal life basically persist with you.

The reason this is important is that different bacteria digest different kinds of carbohydrates. Some make more methane; others help hydrogen to combine with sulfur (from other foods or water) to make hydrogen sulfide. It is the latter that have the odor of rotten eggs and the former that have the “flamethrower” reputation with college kids!

Altering this gas response with medications seems to work only part of the time–part of the problem being that some individuals have more intestinal spasm in response to less gas. Anticholinergic medications work for these spastic gut divers.

Additionally we can eat slowly, chew thoroughly, sip rather than gulp liquids, minimize fizzy beverages, not chew gum, and eliminate sugar-free foods containing sorbitol or xylitol — both are poorly digested and serve up a potent fare for our gas-forming bacterial friends.

If you must eat beans–boil them for three minutes, soak overnight and throw out the water containing the offending carbohydrates. Use of the enzyme “epazote” can also be helpful.

The same advice is good for those who complain of frequent or excessive flatus. If much of the excreted gas is composed of hydrogen and carbon dioxide, which originate in the body, not the air, the problem may be a general malabsorption disorder or difficulty with particular foods. A low carbohydrate diet will often turn down the flatus volume.

In addition to the beans, mushrooms, onions, celery, and other foods containing complex carbohydrates and undigestible fiber, many patients with abdominal complaints also benefit from reducing their intake of lactose, the milk sugar in dairy products. This sugar can cause gas, cramps and diarrhea as can the sorbitol in diet foods like candy, chewing gum, and sugar-free lozenges. Sorbitol is another non-digestible carbohydrate; but, because of its form, people have a harder time making the association between consumption and later discomfort.

Hopefully, this will help explain those cramps in your gut and the terrible odor that your buddy has on those occasions that you both have had black bean soup. Keeping your diet in mind when preparing for a dive just might turn you trip around.


Ernest S. Campbell, M.D., FACS

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