The Process Of Food Digestion Explained


When food is solid we chew it. We swallow it if it is liquid. Then it goes down our throats. It is interesting to learn what happens to food in entire digestive track and how our food habits influence our health, fitness and wellness.

What happens in the mouth?

When we chew our food in mouth it gets broken into small pieces and gets mixed with saliva. Saliva is a colorless watery liquid which is always present in our mouth. It contains enzymes which digest food. These enzymes in saliva convert insoluble starches into water-soluble substances.

Actually this is the process of digestion. Enzymes convert many complex food substances into simpler substances which then can be absorbed by the body and used for its needs. These enzymes are made by different organs / glands. What finally remains after processing of the food in the digestive track is not useful for the body & is thrown out as stools or faeces.

When we smell food, our mouth waters. Saliva starts flowing down from the three pairs of salivary glands — one pair below & in front of each ear, another pair at the back of the lower jaw & the third pair underneath the tongue.

We normally produce about 8 to 10 cups of saliva in a day, in our mouth.

The enzyme in this saliva breaks down carbohydrate into simpler soluble forms of sugar.

The more we break our food by munching, the better. Saliva can then act faster on the food. Thorough chewing helps digestion process. ( It is said, every mouthful of food should be chewed 32 times, once for each tooth ).

Food then passes down our throat through food pipe. The small flexible lid in our food pipe, called epiglottis, closes automatically when we gulp down our food. It prevents food from going down the wrong passage which is wind pipe, lying alongside.

What happens in the stomach?

Stomach is an important bag shaped organ. It constantly contracts and relaxes and churns the food inside. Inside lining of stomach secretes many enzymes.

These enzymes help to breakdown proteins in order to allow body to absorb nutrients. These nutrients are then used up by body for body repair or body growth or as a fuel (energy).

Large number of glands are present inside lining of the stomach. One of the enzymes, called Renin, converts protein from milk, into soft curd. Another enzyme, called Pepsin, breaks down the long protein chains into smaller units called Peptones which are soluble in water.

Stomach also makes a large amount of hydrochloric acid. This is the same acid which we see in the chemical laboratory. This acid does many jobs as follows:

  1. It weakens the proteins by loosening some of their links.
  2. It dissolves minerals from various foods we eat
  3. It kills bacteria which enter our stomach with the food we eat.

Food stays in the mouth for a few minutes but stays in the stomach for hours. maximum secretion of Renin, Pepsin & hydrochloric acid takes place about two hours after eating a meal. Food digestion at this time goes on very actively.

Digestion in the stomach is basically breaking down of proteins into simpler peptone units with the help of two enzymes and hydrochloric acid.

Outflow valve of stomach which remains closed most of the time during the day, opens up occasionally & allows very small amount of semi-digested / digested food to proceed further into small intestine. This valve opens and closes automatically. It allows partly digested semi-fluid, pasty food to pass through to small intestine.

Small intestine process

Small intestine is a long tube which further processes the semi-digested food which comes from stomach.

Top part of small intestine is called duodenum and is about 25 cms long. There are main three juices which digest food in the small intestines. Bile juice, a bitter substance comes from liver.

Second one comes from pancreas and third one from small intestines. Juice from small intestine trickles from many places along the way. Small intestine is quite long about 5 to 6 times longer than your own height. It is properly folded in the abdomen. Most of the digestion takes place in this small intestine.

The digestion process is somewhat complicated. Pancreatic juices contain many enzymes and hormones. These help breaking down of peptones ( derived from proteins ) into individual amino acids.

Pancreatic juice also digests both fats and carbohydrates. Carbohydrates get converted into soluble glucose by pancreatic juice. Similarly, Lactose ( present in milk ) is also converted into soluble glucose.

Fats are digested to give simpler substances with the help of another kind of secretion of liver.

The liver is the chemistry laboratory of the human body.

Blood flows from heart to liver. The liver controls the level of sugar in the blood & storage of such sugars in the muscles. It takes amino acids from the blood and makes them into proteins and stores it.

It releases these proteins when required by the body. It also destroys poisonous substances and stores vitamins and minerals.

All the food which is by now broken down into simple, mostly water soluble substances is absorbed in the body through small intestine.

The inner lining of the small intestine has a number of tiny, finger like projections called villi. These are sucking organs which seize the digested materials and transfer them to the blood. Blood carries these nutrients through circulatory process to various organs of the body.

Some part of digested fats also gets carried away through another network called lymphatic system. This system also empties its contents in blood, somewhere near the neck.

Vitamins and minerals are often water soluble and are not broken down further & absorbed in the blood after being detached from the food when other nutrients get digested. Vitamin A which is fat-soluble, gets absorbed in the small intestine somewhat like fat itself.

Food which we eat finally reaches blood. It is then carried to all parts of the body, to supply their needs of energy and the body building and regulation of body functions.

Large intestine process

The large intestine is situated next to small intestine and is tubular in shape. Its inside is smooth without any projections. It is placed in abdomen in the shape of English letter U upside down.

As the digested food passes along the intestine, water is absorbed from through the walls and into the blood. The food becomes less liquid and becomes hard. Breaking down of the digested food gives rise to some substances which carry bad smell. The undigested food is then thrown out of the body in the form of stools through the opening called Anus.

How the digested food is made useful?

Carbohydrates (starches & sugars) are broken down first in mouth and then in the small intestine into simple sugars chiefly glucose. Glucose is absorbed by the villi of the small intestine directly into the blood stream. It travels all over your body and is used by muscles as a source of energy for their working.

A small part of glucose is converted into glycogen which is the form in which glucose is stored both in muscles (about two thirds) and in the liver (about one third).

Some glucose is always circulating in the blood and the level is steady. When the sugar level goes up it is a sign of a fault — such as the disease diabetes.

Fats are broken by way of intermediate simpler forms eventually into glycerol & fatty acids. Part of these fatty acids directly go into the blood and then to the liver as does glycerol. These fatty acids are either used for energy or sent via blood to other parts of body. They then may be used for energy or built back into fats, which are despatched through the blood for storage as fatty tissues.

Any excess food which we eat above our requirements is converted into and stored away mostly in the form of fat. When we get insufficient food (e.g. during fasting) fat deposits are first used up.

Proteins reach blood stream as amino acids which are their building blocks. At various places in the body, these amino acids are picked up by the body organs and built into variety of compounds.

Tissue proteins, enzymes, hormones and so many other chemical compounds are protein in nature. Liver itself makes and stores body proteins.

Vitamins and minerals are also stored in the liver. Whenever body needs them, these are released to the body parts and organs.


There are thousands of interconnected processes going on in our body, all the time. Food is digested and then absorbed in the small intestine. All the absorbed vital nutrients are then circulated via blood to different body parts / organs. And the process goes on.

Please follow and like us:

Leave a Reply

Your email address will not be published. Required fields are marked *