You may be surprised to find out that normal people pass gas an average of 13.6 times a day (the normal range is between 6 to 20 times a day). We produce and rectally pass between 500 to 2000 ml of flatus per day with the average man passing 110 ml per episode and the average woman passing 80 ml per episode.
Intestinal gas is mostly (99%) carbon dioxide from digestion of protein and fat, hydrogen from digestion of carbohydrate and protein, nitrogen and oxygen from swallowed air, and methane from gut bacteria. These are all odorless gasses, but that remaining 1% can be olfactorily challenging. Certain microorganisms in our gut produce methanethiol, dimethyl sulfide, and hydrogen sulfide which along with some short chain fatty acids may cause your neighbors to pinch their noses when you walk into the room.
Except for swallowed air, most intestinal gas comes from the foods we eat. Some foods are notorious for gas production. You may have heard the term FODMAP which stands for Fermentable, Oligosaccharides, Disaccharides, Monosaccharides, and Polyols. These are foods which may not be absorbed well in some people and can increase the volume of bowel gas.
The oligosaccharides that may cause us trouble are found in wheat, barley, rye, onions, artichokes, peas, cashews, legumes, and lentils. The disaccharides are almost all in lactose-based dairy products: milk, custards, ice cream, and yogurt. The monosaccharides are fructose-based sugars found in apples, pears, cherries, asparagus, honey, and of course high fructose corn syrup. Polyols (sorbitol, mannitol, and xylitol) are found in stone fruits (peaches, nectarines, etc.) and in apples, pears, cherries, cauliflower, and artificially sweetened foods including chewing gum.
The worst offenders in terms of the volume of gas produced are beans, carrots, raisins, bananas, onions, and milk products (for those of us with lactose intolerance). Next are foods with a lot of complex carbohydrates, such as pastries, potatoes, citrus fruits, apples, and bread. The least likely to cause gas are meat, fish, grapes, berries, nuts, eggs, rice, and gluten-free grains.
Elderly patients may complain about gas symptoms which are more due to swallowed air from poorly fitting dentures, but also from the medications they take (NSAIDs, laxatives, and statins), slower digestion, and constipation. Younger patients who eat quickly, smoke, or chew gum may also have more swallowed air on top of their normal digestive production of flatus.
So, what do we tell our patients with too much gas? First, ask about worrisome symptoms such as weight loss, anorexia, diarrhea, travel, or pain, and work up the symptoms appropriately. Health conditions such as constipation, irritable bowel syndrome, celiac disease, lactose intolerance, and giardiasis can usually be readily worked up.
If there are no worrisome symptoms or signs by history or exam, have your gaseous patient keep a flatugraphic diary to record the number of times he or she passed gas and what he or she ate that day. Quick hits for those patients with over 40 flatulent episodes per day are to avoid lactose (or add lactase) and avoid the worst offenders: beans, broccoli, cabbage, cauliflower, raisins, lentils, onions, prunes, and apples.
If smelly odor in flatus is the main problem, activated charcoal underwear absorbs 100% of sulfur-based gasses. Activated charcoal seat cushions can also be used, but they only absorb 20% of the odorous gasses. Particular care should be used when flying on commercial aircraft. Planes are only pressurized to 8000 feet and gas will expand in the gut. My medical recommendation to avoid pain or injury is to pass the gas. I realize this may be a problem, since only 50% of air on a plane is recycled. For the sake of one’s fellow passengers, individuals who are sulfide-producing gas machines can (and probably should) consider wearing activated charcoal underwear when taking to the friendly skies.
Jim Cotter, MD