All About the Gas You Pass

Tamara Duker Freuman


Although intestinal gas is relegated to the realm of bathroom humor in our culture, the fact is that excessive gas is not funny at all for the countless people beleaguered by chronic bloating, abdominal pain and socially inconvenient reality of excessive flatulence. Fart jokes may draw a cheap laugh, but there's nothing amusing about having to cancel plans all the time due to debilitating gas pain or bloating.

As uncomfortable and socially undesirable as intestinal gas may be, it's important to mention that it's entirely normal, and generally an indication that things are working as they should be. People pass gas 12 to 20 times per day on average, and men typically pass more gas than women. But just because it's normal, gas may not always be comfortable or convenient. This is particularly so for many people with Irritable Bowel Syndrome, who can be very sensitive to pain from even minor distention of the gut wall. When patients have gas that's become so problematic that they find themselves in my office seeking professional help, the common question I get is: What's causing all this gas?

On the surface, the answer is pretty straightforward. Intestinal gas generally derives from one of two sources. Primarily, the gas we pass is a byproduct of bacterial fermentation of various carbohydrates in the colon (large intestine). When bacteria feast on undigested carbs -- including various fibers, resistant starches, unabsorbed sugars and unabsorbable sugar alcohols (polyols) -- they produce gas as a byproduct. This gas is generally methane or hydrogen. Protein and fat are far less fermentable by gut bacteria, and they tend to be fully absorbed well before arriving in the colon. For this reason, people who follow very low-carb diets -- particularly those which do not contain artificial sugars and lots of vegetables -- often find that they are less gassy compared to when they follow a normal, mixed diet.

[Read: Coping with Intestinal Gas .]

Some of the healthiest, most nutritious foods one can eat are highly fermentable: beans, lentils, cabbage, broccoli, artichokes, onions, garlic and many types of whole grains. When we eat these fermentable foods, the health benefit is twofold. First, our bodies extract the vitamins, minerals and antioxidant-rich phytochemicals that these foods contain to use in maintaining normal cell function. Second, our bodies benefit from metabolic byproducts of the fermentation process carried out by gut bacteria -- such as short-chain fatty acids -- which nourish the cells of the intestinal lining itself and exert beneficial changes in the pH of the colon that facilitate other important metabolic reactions. In other words, intestinal gas is a sign that your gut bacteria are being well fed and paying it forward.

But if excess gas becomes problematic, it can be helpful to modify the diet to emphasize healthy foods that are relatively less fermentable by gut bacteria. This is the principle behind the Low FODMAP diet. Alternatively, using a supplemental enzyme like Beano can help pre-digest certain plant fibers so there's less of them available to be fermented by colonic bacteria -- and therefore, less gas.

[Read: IBS? Could be the FODMAPs.]

Less commonly, intestinal gas can result from aerophagia, or swallowing air. Air contains nitrogen gas, which does not diffuse into the bloodstream like its gaseous friends, oxygen and carbon dioxide. Swallowed air that does not get belched out from the stomach, therefore, gets trapped in the intestines, and must make its way all the way through the intestines before it can exit via the rear door. Some indications that you may be swallowing air include excessive belching in addition to frequent intestinal gas; normal bowel movements despite an increase in intestinal gas; and the absence of a foul odor when passing the intestinal gas. I often see aerophagia among people who eat quickly or talk while eating; opera singers; heavy exercisers; and folks with chronic sinus problems and allergies, who habitually snuffle or snort back excess mucus or experience chronic post-nasal drip. In such cases, remedies such as mindful eating; drinking from a straw; tucking the chin down when swallowing food; drinking seltzer with meals to induce belching; and using simethicone with meals can be helpful.

If you're trying to play Sherlock at home, a detailed food and symptom journal is a good place to start. Mark down the times of everything you eat (brands included), as well as times of the onset of your troublesome gas. Assuming your bowel transit time is normal, a good rule of thumb is that gas results from food you ate six to eight hours prior -- for this is the time it takes for a solid, mixed meal to travel from mouth to colon. So, if you start to become excessively flatulent after lunch (around 2 to 3 p.m.), look back to see what potentially-fermentable foods you ate for your 8 a.m. breakfast, not what you ate at lunch. Although gas does typically onset soon after eating, this is because the meal you most recently ate propels the previous one to two meal(s) forward into and through your colon. If you wake up very flatulent, look to dinner the night before.

When trying to make sense of your sleuthing, beware of the confounding effect of processed foods. Commonly, I'll see patients falsely blame wheat or gluten for their gas problems based on a bad reaction to an energy bar, fiber-enriched English muffin or protein-enhanced breakfast cereal. In these cases, it's far more likely that gas was caused by another highly fermentable food additive, such as soy protein concentrate, inulin (chicory root fiber) or a low-calorie sweetener such as xylitol or sorbitol. Finally, I've noticed that a lot of my patients are quick to eliminate gluten and dairy when excessive gas and bloating is a problem. When symptoms persist despite this elimination, however, most of them insist on staying gluten and dairy-free indefinitely. I often need to remind people that you can't react to something you're not actually eating. If you haven't eaten wheat or dairy in three days and you're still extremely gassy, then you can't blame the wheat or dairy! In these cases, assuming celiac disease has already been ruled out, I encourage my patients not to restrict themselves any more than necessary.

[Read: What is Non-Celiac Gluten Sensitivity?]

Lastly, if intestinal gas is particularly malodorous, and/or is accompanied by urgent, loose stools/diarrhea, light-colored stools, or oily/floating stools, something may be amiss that warrants a trip to your doctor. Such symptoms often suggest the possibility of malabsorption: proteins, sugars or fats that would normally be absorbed in the small intestine are not being absorbed there, and are instead travelling further into the colon to serve as fermentable substrates for the gut bacteria. Malabsorption can be benign but uncomfortable, as in the case of lactose intolerance or fructose intolerance. Or it can reflect something more serious, like celiac disease, Crohn's disease or pancreatic insufficiency. Your doctor can test for all of these conditions with breath tests, blood tests, stool tests and/or endoscopy if s/he suspects them based on your symptoms and diet history.


Tamara Duker Freuman, MS, RD, CDN, is a registered dietitian whose NYC-based clinical practice specializes in digestive disorders, celiac Disease, and food intolerances. Her personal blog, www.tamaraduker.com, focuses on healthy eating and gluten-free living.