How the gastrointestinal tract works
Before we go into why you can get a bloated stomach after a meal, we must explain how the gastrointestinal tract works (under normal conditions).
The most important function of the stomach is to digest (break down) proteins with the help of an enzyme and to sterilize the food with the help of hydrochloric acid. Together, the enzymes and acid transform the food into a bacteria-free gruel-like soup which is then emptied into the duodenum. In the duodenum, the food is mixed with other enzymes from the pancreas that help break down fat, carbohydrates, protein, and DNA, but also with bile from the liver that atomizes the fat into microscopic drops, all so that the nutrients can be absorbed in the small intestine. The wall of the small intestine also contains lactase, which breaks down milk sugar. The lining of the small intestine is made to be able to absorb nutrients from the intestinal contents and its folded surface is about the same size as the surface of a badminton court. Dietary fibers that are not broken down by amylase from the pancreas continue through the small intestine to the large intestine. The large intestine contains a large number of bacteria that can break down these dietary fibers. During this decomposition, gas (especially carbon dioxide, hydrogen, and methane) and by-products are formed. The large intestinal mucosa is well adapted to handle the products of the bacteria's metabolism. In the large intestine, water, salts, and also beneficial short-chain fatty acids such as butyric acid and propionic acid are taken up to the bloodstream. The bacteria in the colon also produce vitamin K, which is absorbed into the bloodstream and plays an important role in blood coagulation.
Common reasons for bloating
Gas is produced under normal conditions by bacteria in the colon. It takes 3-4 hours for the stomach to be emptied and another 3-7 hours for the food to pass through the small intestine to the large intestine. This means that gas production in the large intestine can take place 6-11 hours after a meal, i.e. when the intestinal contents have reached the colon. The reason for the gas to be produced in the large intestine is, for natural reasons, that the rectal opening is adjacent to the large intestine and can release these gases. Fiber-rich food (for instance containing the dietary fiber inulin) that nourishes the bacteria in the colon inevitably results in gas production.
Foods that contain inulin are:
- Jerusalem artichokes
Other foods that contain dietary fiber that can result in gas production:
- Dried fruit
- Kidney beans
- Red beans
If it takes 6-11 hours for the dietary fiber to reach the colon where the fibers are digested by the bacteria there (producing gas), how can it be that you can have problems with a tense, gassy and swollen stomach already 3-4 hours after the meal, that is, when the food has only reached the small intestine?