The digestive system

Digestive phenomena

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Intestinal wind is expelled at both ends of the digestive tract.

  • When expelled through the mouth, it is called belching (or burping).
  • When expelled through the anus, it is called flatulence (or farting).

Intestinal gases are produced by bacteria in the colon when there is fermentation of leftover food.

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Intestinal wind

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The digestive tract contains intestinal gases. Release of these gases through the anus is quite normal and is actually a sign that the digestive tract is functioning well. On average, a person releases 0.5 to 1.5 litres of gas each day, over the span of 12 to 25 episodes. These gases are released at the two ends of the digestive tract – either at the mouth (through burping) or at the anus (through flatulence).


Intestinal gases consist of nitrogen, oxygen and carbon dioxide produced by the bacteria present in the digestive tract. These bacteria ferment food residues and gas is released during this breakdown process.

There are also hydrogen, methane and sulphur-containing substances. These sulphated gases have a distinct odour, and the human nose can easily detect concentrations of hydrogen sulphide, even low ones.

Fermentation of certain kinds of food generates more gas than others, namely pulses such as kidney beans. Their outer shell has a large amount of sugar, which the intestinal flora easily ferments. Starchy food such as pasta, corn and wheat can also generate gas during fermentation.

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