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Straight, No Chaser: Eructation (Belching) and Flatus (The Other One)

By Jeffrey Sterling, MD October 26, 2020


It seems like Straight, No Chaser is spending the week addressing your digestive system, so why not continue the theme? Here’s one of those conversations that everyone wants to have but rarely does. Gas is a natural phenomenon. That’s a given. However, all of us probable want to and would benefit from knowing why it’s happening and what can be done to minimize those odoriferous emanations from above and below. Here are some frequently asked questions on the gas you pass.


What is gas?
Gas is a byproduct of the digestive process or of your swallowing air. It’s some combination of oxygen, carbon dioxide, hydrogen, nitrogen and methane gases. Remember the digestive tract extends from your mouth to your anus, so depending on where the gas is produced, the gas may be expressed from either end of you through burps or flatus.
Why would I swallow air?
Everyone swallows a small amount of air when eating and drinking. The amount of air swallowed increases when people eat or drink too fast, chew gum or suck or hard candy, drink carbonated beverages, smoke or wear loose-fitting dentures.

 belching cows

Why does gas have that smell?
Flatus (gas passed through the anus) may contain small amounts of sulfur. Flatus that contains more sulfur gasses has more odor.
Why do I produce so much gas? 

  • Passing gas is normal. In fact, the average person does so about 15-20 times a day. Many things can cause you to produce more, including eating a lot of carbohydrates (e.g. sugars, starches, fibers). The upper parts of the digestive system (stomach and small intestines) are as effective as the lower intestines as breaking down carbohydrates. When the lower intestines do so, gases including hydrogen, carbon dioxide, methane gas or hydrogen sulfide (a sulfur gas – as mentioned, methane and sulfur as more noticeably smelly gases). This isn’t as much of an issue with fat and protein based diets.
  • Constipation also results in increased amounts of methane production.
  • Conditions that disrupt the digestive system can have the same effect. Examples include diabetes and Crohn’s disease.

 flatulence foodsflatusbeans

Can you give examples of foods that are carbohydrates and cause gas?
There’s wide variation between individuals in how foods are digested. As an example, consider the effect of being lactose intolerant. Some foods that may cause gas include

  • fruits such as pears, apples, and peaches
  • vegetables such as broccoli, cauliflower, cabbage, Brussels sprouts, onions, mushrooms, artichokes, and asparagus
  • whole grains such as whole wheat and bran
  • sodas; fruit drinks, especially apple juice and pear juice; and other drinks that contain high-fructose corn syrup, a sweetener made from corn
  • beans
  • milk and milk products such as cheese, ice cream, and yogurt
  • packaged foods—such as bread, cereal, and salad dressing—that contain small amounts of lactose, a sugar found in milk and foods made with milk
  • sugar-free candies and gums that contain sugar alcohols such as sorbitol, mannitol, and xylitol


What are the symptoms of gas?
In addition to burping and passing gas, bloating and abdominal discomfort are common.
When should I be seen for gas?
It’s easy to be distracted by what you believe to be simple gas pains. If your symptoms are new or different (especially if you’re above age 40), or if your gas symptoms are accompanied by diarrhea, constipation or weight loss, you should get evaluated. Of course, severe pain seems to be the most common prompt for an evaluation.
Another Straight, No Chaser post will address prevention and treatment of your belching and flatus.
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