GI and EDS/HSD Part II

Dec 31, 2021 | Samantha Campbell | @samanthacmaa

What is normal?

Before discussing what is abnormal, it is always good to understand what is normal. Everybody makes gas in the intestinal tract. In fact, the average person produces at least 750-1000 ml of gas each day (that is the size of a one-liter bottle). At any one time, most people have approximately 200 ml of gas in their intestinal tract (that is approximately equal to 8 ounces of fluid, or one cup). In addition, the average person passes gas from the rectum 15-18 times per day.  Some people produce much more gas than that, often because of what they eat. Most gas produced in the gastrointestinal tract is produced in the colon (also called the large intestine). The colon contains many bacteria, and these bacteria help finish the process of digesting food. In fact, there are nearly 1,000 different types of bacteria in the colon. During the final process of digestion, when liquified food arrives in the colon, the bacteria act to help break down the liquified food and gas is produced. Most of the gas produced in the colon is either hydrogen or methane. The production of gas in the colon may lead to symptoms of bloating and distension in some people.

What is abnormal?

Despite understanding how gas in the intestinal tract is produced and recognizing that symptoms of gas and bloating are quite common, there are no agreed upon standards for what is considered abnormal. We know that certain types of diets create more gas than other types of diets. For example, people who take in larger quantities of protein, but only small amounts of fruits and vegetables usually produce less gas than people who eat very little animal protein but take in greater quantities of fruits and vegetables.  We also know that certain types of foods create more gas than other types of foods (see below). In addition, the amount of gas produced reflects the different mixture of bacteria in the colon, and this varies from person to person. In general, health care providers do not focus so much on what is abnormal in terms of gas production, but rather what is bothersome to the patient.


Abdominal gas and bloating can occur for many reasons. However, there are five major causes, which will first be briefly listed and then reviewed more carefully. These causes include: diet; disorders of intestinal transit (how things move through the gastrointestinal tract); too many bacteria in the small intestine (also called small intestinal bacterial overgrowth); disorders of gut sensation (how gas in the intestinal tract is felt or sensed); and an abnormal reflex that involves the abdominal wall and the gastrointestinal tract.

One of the most common causes of gas and bloating is diet. As discussed previously, when partially digested (broken down) food reaches the large intestine (colon), the bacteria in the colon finish the process of digestion. During this final process of digestion gas is produced. Some foods produce more gas and bloating than others. Some of the worst offenders in terms of gas production include: dairy products (milk, ice cream, cottage cheese, cheese) for those who are intolerant to lactose (lactose is the milk sugar); high fructose corn syrup (found in soft drinks, some energy drinks and sports drinks); cruciferous vegetables (broccoli, cauliflower, cabbage, brussel sprouts); legumes (red beans, black beans, baked beans, lentils, garbanzo beans, hummus); onions, garlic and peppers; and foods with fiber (many fruits and vegetables and whole grains). It is important to note that eating fruits and vegetables and whole grains is part of a healthy diet. It is recommended that adults eat approximately 25 grams of fiber each day.  But, in some patients these foods can produce more gas and bloating than other types of foods. This is not dangerous, but it can be uncomfortable.

A second major cause is related to disorders that affect how materials move through the gastrointestinal (GI) tract. These are often called disorders of GI transit. Two of the most common disorders associated with gas and bloating are chronic constipation and IBS-C - irritable bowel syndrome with constipation (IBS). Both disorders are characterized by symptoms of constipation, which can include skipping days without having a bowel movement, or straining at stool, or passing hard stool. Many patients with these symptoms of constipation also have difficulty evacuating gas and this can lead to chronic symptoms of gas and bloating.

The third major category is that of small intestinal overgrowth (also called SIBO). Normally, very few bacteria live in the small intestine. Patients who have small intestinal bacterial overgrowth have a problem with too many bacteria living in the small intestine. These bacteria process food sooner than usual and this can cause symptoms of gas and bloating.

The fourth major category associated with symptoms of gas and bloating is that of a disorder of gastrointestinal sensation. The clinical term for this is visceral hypersensitivity. Simply stated, this means that some people sense things differently in their gastrointestinal tract. They may sense very low levels of pain or discomfort that others don’t feel. They may sense low levels of discomfort, but their brain interprets the low levels of discomfort at much higher levels. This hypersensitivity to pain or discomfort in the GI tract is common in patients with IBS.

The fifth major category is that of an uncommon disorder related to how the muscles of the abdominal wall work with the intestinal tract.  Normally, when gas in the intestinal tract stretches the small intestine or large intestine, the muscles of the abdominal wall automatically contract so that the abdomen does not bulge out. Contraction of the abdominal wall muscles will minimize symptoms of distension. However, in some patients this automatic contraction does not occur, and in fact, the muscles inappropriately relax rather than contract. This means that when the large or small intestine stretches due to gas, the abdomen (your belly) may become more distended. Why this occurs in some patients but not others is unknown. Our next post on this topic is the most anticipated – Treatments. So, keep following here!

Author: Brian Lacy, MD, PhD

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