How Long Does It Take To Digest Food? - Donat

The mouth: the entry point of the digestive tract

Digestion starts in the mouth or, according to some definitions, even before that. Indeed, the salivary glands are activated as soon as we see or smell food. Once food enters the mouth, we chew it down into more easily digestible pieces. With each bite, enzymes in the saliva break down the starch to make it easier to swallow, and then the tongue moves the food towards the oesophagus.

The oesophagus: the link between the mouth and the stomach

When food is eaten, chewed and swallowed, it passes down the oesophagus, which lies in the throat, next to the windpipe. The windpipe is protected by a small elastic flap called the epiglottis, which folds over it to prevent food particles from entering and causing choking.

Food then travels down the oesophagus through a process of muscle contraction and stretching, known as peristalsis. But before it can enter the stomach, a muscle called the lower oesophageal sphincter must relax. Once this happens, food can enter the stomach, and the sphincter then closes off immediately so that it doesn’t return to the oesophagus or the mouth.

When this muscle relaxes too much, the stomach contents can flow back into the oesophagus or mouth, which we call acid reflux or heartburn. Read the article on heartburn to learn how to overcome this problem before it leads to more serious complications.

Stomach: breaking down food

The stomach is a hollow organ that functions as a kind of container for food. This food is mixed with stomach enzymes and acid, which break it down. Once the food is sufficiently digested, it can continue its journey to the small intestine.

Small intestine: absorption of nutrients

The small intestine is a long muscular tube divided into three segments:

• The duodenum is the first section of the small intestine, responsible for continuing digestion.
• The jejunum and ileum are in charge of the absorption of nutrients into the bloodstream.

As food is transported through the small intestine by the action of peristalsis, it mixes with the digestive juices of the pancreas and liver, which speed up the process of food breakdown. The cells of the small intestine use their cilia to absorb the key nutrients and water that are essential for our bodies.

Food enters the small intestine in semi-solid form and leaves it as a liquid. Once the nutrients are absorbed, the remaining, undigested food continues its journey into the large intestine.

Let’s also have a quick look at the roles of the pancreas, liver, and gallbladder:

• The pancreas supplies the duodenum with digestive enzymes, which are needed to break down proteins, carbohydrates, and fats. It also produces insulin, the main hormone for metabolising sugar.
• The liver also handles the nutrients absorbed by the small intestine. It helps digest vitamins and some fats by secreting bile. The liver is often described as the body’s chemical factory. It converts the substances absorbed by the intestines into a variety of biological compounds needed by the body. It also acts as a filter, breaking down and eliminating harmful substances.
• The gallbladder stores bile from the liver and passes it to the duodenum, where it helps in the digestion of fats.

Large intestine

The large intestine is the muscular tube that connects the small intestine to the rectum. Its role is to process waste materials and prepare them for removal from the body.

It usually takes 6 to 8 hours for food to pass through the stomach to the small intestine, and from there to the large intestine. Once partially digested food has made its way to the large intestine, it can stay there for more than a day, breaking down even further. The remaining water and nutrients that might be of use to the body are absorbed, while the rest is converted into stool. The latter is made up of food residues and bacteria.

Stool passes through the large intestine by means of peristalsis. Initially it flows in liquid form, but becomes solid when the water is removed. Roughly twice a day, it is passed to the next stop: the rectum.

The rectum and anus: where digestion ends

In about 2 to 3 days, the food you have eaten should have moved through your digestive tract to its last stop.

The rectum receives the stool from the large intestine and sends signals to the brain that it needs to be emptied. If the brain gives permission, the sphincter relaxes, while the rectum contracts and pushes the stool out through the anus. The latter is flanked by the pelvic floor muscles and two sphincter muscles, which prevent any accidental release of stool.