Excessive Flatulence | Causes of Lower Gut (Bowel, Colon) Gas

Gas in the lower gut, which includes the latter part of the small intestine, colon and rectum, is passed out of the system as flatus.  Most of the gas that enters or is produced in the upper gut is evacuated through belching, however, small amounts do pass into the lower gut to be passed out as flatus. Normally, a person passes flatus anywhere between 15 to 20 times in a day. The volume, odor and even sound of the flatus that is passed may vary from person to person and even during the course of the day.

Anywhere between 1,000 milliliters to 2,000 milliliters of gas is produced in the gut per day. This is primarily a result of chemical digestion and bacterial fermentation. Most of this gas is evacuated from the bowels but about 200 milliliters remain within the gut.

Bacteria in the bowel produce most of the gas in the lower gut. The large intestine has the largest population of these bacteria, which ingest remnants of food and waste matter in the colon. This is known as microbial fermentation. It is a vital process since these colonic bacteria produce vitamin K and enzymatically digest any remaining carbohydrates in the bowel. These nutrients are then absorbed by the the colon wall.

The main gases that accumulate in the bowel due to bacterial fermentation includes methane, carbon dioxide and hydrogen. Small amounts of nitrogen pass from the bloodstream into the lumen of the gut. This is eventually expelled from the rectum during a bowel movement or during the course of a day as flatus.

Other Symptoms Associated with Excessive Flatulence

Causes of Excessive Flatulence

Apart from the normal process of gas production explaineded above, there are other contributing factors to the gas in the gut that are not pathological (due to disease). Some of these may also result in excessive flatulence but in most cases, the gas is passed out in belching. This includes :

Other non-pathological factors that may contribute to both excessive belching and excessive flatulence includes :

  • ‘Gassy’ foods (refer to Gassy Stomach)
  • High fiber diets
  • Medication

Impaired Digestion

Digestive problems (maldigestion) may arise for a number of reasons. Deficiency and inactivity of certain digestive enzymes prevents nutrients from being absorbed from the gut. This residual nutrition allows intestinal bacteria a larger nutrient supply for consumption thereby increasing the gas production in the gut.


A number of gastrointestinal infections can disrupt the normal physiological processes within the gut. Via various mechanisms, these infections may lead to excessive gas in the gut. Even after the infection resolves, a disturbance in the population of the normal intestinal flora (bowel bacteria) may continue to contribute to excessive belching and flatulence.

Refer to Stomach Infections for other causes.

Delayed Transit

If the transit of food and waste materials through the gut is delayed, either as a result of a disorder with gut motility or an obstruction (or pseudo-obstruction), the normal intestinal bacteria will have a longer period of time to consume residual nutrients thereby producing excessive gas.


Irritable bowel syndrome (IBS) is a functional bowel disorder the cause of which is not clearly understood. Excessive flatulence is often reported in IBS, both in constipation-predominant and diarrhea-predominant IBS. The exact cause of this excessive gas is also not clearly understood but may be due to impaired transit of intestinal gas (Reference 1).

Related Articles


  1. Impaired transit and tolerance if intestinal gas in IBS.

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