Tout savoir sur la digestion des aliments - Epycure

NUTRITION Everything you need to know about food digestion


5min reading time

What is digestion for?

Digestion transforms the food we eat into molecules that can be assimilated by the body. The digestive system is made up of a succession of organs, each of which plays a specific and essential role in digestion.

Food is transformed by mechanical and chemical digestion processes. Mechanical digestion makes it possible to soften and reduce food to mush during chewing and to mix the food bolus thanks to contractions of the stomach. Chemical digestion , which takes place throughout the digestive tract, dissolves nutrients and breaks down assimilable elements using digestive enzymes and digestive juices.

Thanks to these two processes, the complex molecules that we ingest are transformed into simpler elements that are more easily absorbed by the body: carbohydrates, proteins, lipids, vitamins, minerals and trace elements.

After their absorption in the digestive tract, the nutrients pass into the blood and are directed to the liver, which will distribute them to the rest of the body or store them. All of this provides our body with the necessary energy and nutrients it needs to function. Indigestible substances such as fiber are compacted in the form of stool and passed through the anus at the end of digestion.

Digestion is a long process that lasts about 24 hours and varies depending on the amount of food ingested and the fat content. In fact, the fattier a meal, the longer it will digest.

What are the main stages of digestion?

As the meal approaches, even before the first bite, a signal is sent to the digestive organs to begin digestion. Thus, the mouth salivates, the stomach contracts, the pancreas and the gallbladder secrete digestive juices. The food journey can be summarized in four main stages.


Digestion begins in the mouth through chewing. The food bolus is cut, ground by the teeth and impregnated with saliva . Saliva has 3 essential roles. It makes it possible to moisten foods, reduce their size to facilitate swallowing and the action of digestive juices but also to begin the digestion of carbohydrates thanks to enzymes called amylases . Starch molecules present in bread, pasta or potatoes for example, are transformed into glucose.

The food then travels down the esophagus, thanks to muscular contractions, and arrives in the stomach.

This step is essential, since chewing your food sufficiently allows you to optimize and facilitate digestion in the rest of the digestive tract.

Gastric digestion

Once the food has reached it, the stomach contracts to churn and grind the food bolus into smaller pieces. The cells in its wall secrete gastric juices , a mixture of enzymes and hydrochloric acid. Enzymes will allow complex molecules to be broken down into simpler elements that are more easily absorbed by the digestive tract. Some enzymes begin the digestion of proteins and fats by breaking them into amino acids and fatty acids, respectively.

These partially digested foods and mixed with gastric juices form a slurry, called chyme , which will gradually pass into the small intestine.

Intestinal digestion

The chyme now passes into the duodenum which is the first part of the small intestine, the longest organ of the digestive tract, approximately 7 meters long. This organ allows both to continue to break down food, but also to absorb nutrients from digestion.

Thus, the chyme undergoes the action of new gastric juices upon arriving in the duodenum:

  • Pancreatic juice , secreted by the pancreas, neutralizes the acidity of gastric juices and finishes breaking down starch into glucose,
  • Intestinal juice , coming from the intestine, and pancreatic juice ensure the final breakdown of large molecules such as proteins and lipids, which they transform respectively into amino acids and fatty acids,
  • Bile , a liquid produced by the liver and stored in the gallbladder, plays a special role because it does not contain enzymes but bile salts. Thanks to them, it solubilizes fats and facilitates their intestinal absorption.

This long journey through the intestine gives our body enough time to absorb different nutrients through the cells of the intestinal wall. Once assimilated, the nutrients useful to the body pass into the bloodstream to be distributed to the different organs of the body. Only indigestible materials such as dietary fiber and part of the water they contain continue on their way to the large intestine.

Colic digestion

The large intestine, known as the colon, is shorter than the intestine and measures only one and a half meters. At this stage, the majority of digestible substances have already been absorbed, only the indigestible materials mentioned above are found at the entrance to the colon. Thus, its role will be to recover the remaining water in these indigestible materials, then to compact them in the form of stool . These wastes are stored in the rectum and are evacuated through the anus. Once these excrements are eliminated, it is the end of the digestion process.

The intestinal flora

Our digestive system is accompanied by our intestinal flora, also called intestinal microbiota. It is found in the terminal part of the small intestine but also throughout the colon. It is made up of many beneficial microorganisms, approximately 10,000 billion “friendly” bacteria. They are capable of completing the digestion of certain proteins such as amino acids present in undigested materials and indigestible fibers sometimes leading to gas and flatulence when foods are rich in sulfur (cabbage, onion, eggs) or in milk proteins. . It plays an essential role in the body because it participates in the functioning of the immune system, protects the body against potentially dangerous bacteria, participates in the synthesis of certain vitamins and can neutralize toxins produced by germs causing intestinal infections.

Troubles & solutions

Several factors can destabilize the intestinal flora such as drug treatments, germs, food intolerance, poor diet, a peak of stress or fatigue, a lack of water or even a digestive disease. An imbalance in this intestinal flora, or dysbiosis, could contribute to susceptibility to infections, digestive disorders and food allergies. Among the most common disorders, we find stomach burning and cramps, regurgitation, bloating, diarrhea, and even constipation. They are most often benign but they can be very bothersome.

There are simple solutions to promote good digestion. Eat more soluble fiber like carrots, zucchini, sweet potatoes or oatmeal. Avoid fatty, spicy foods, fermenting vegetables like cabbage or artichoke, and carbonated drinks. Drink at least 1.5 liters of water per day. Take at least 20 minutes to eat, in a calm environment, to optimize the work of the digestive tract. Practice gentle, regular physical activity such as pilates or yoga. You can also turn to food supplements such as probiotics to soothe your digestive problems and facilitate digestion.

Solène Senejko

Ingénieure Alimentation & Santé