Process of Digestion

What Happens to Food After You Eat

digestion1Digestion is the breakdown of food into small molecules so they can be absorbed into the blood.

The GI tract is a series of connected organs leading from the mouth to the anus. The digestive system can be up to 30 feet in length, which makes a very long tortuous organ.

Digestion begins the minute food enters inside the mouth. That food travels through the hollow tube of the esophagus, enters the stomach, travels through the small intestine, then the large intestine, and finally empties out from the rectum through defecation. Along the way it receives digestive enzymes from the liver and the pancreas.

First, there is a mechanical digestion of food, where large pieces of food are broken down into smaller pieces. Second, there is a chemical digestion where these small pieces of food are further broken down into even smaller molecules, where they can be absorbed into the blood stream.

Digestion starts in the mouth where you chew the food, where there is contact with saliva. The saliva has mucus and makes the food softer and more lubricated, which allows you to swallow dry foods such as bread and meat. The saliva even contains digestive enzymes such as amylase, where the starch in the food starts being digested. There are glands called the salivary glands that produce amylase and release into the mouth. After the process of chewing, the food that is ready to be swallowed is called a bolus.


digestion2There are individuals with diseases where there is a lack of saliva production by the salivary glands, and they have a difficult time initiating a swallow. For example, individuals with Sjogrens’s Disease have a lack of adequate saliva and tear production, leading to a dry mouth and dry eyes, and difficulty swallowing dry bolus of food.

The bolus travels down the tubular esophagus into the stomach by a process called peristalsis.


digestion3The esophagus has an organized way of squeezing from top to bottom, and guide the bolus down into the stomach.  There is disease of the esophagus where this peristaltic action is disturbed, leading to inability to swallow food.  Achalasia is an example.


digestion4Once the food reaches the stomach, it mixes with gastric juice, where protein digestion begins. The gastric juice contains pepsin and hydrochloric acid. While the bolus is getting exposed to acid and pepsin for digestion, the stomach continues to contract, which further helps mix the nutrients with the gastric enzymes. After several hours, this mixture becomes a thick liquid called chyme.

Chyme slowly empties into the first portion of the small bowel (Duodenum) where it mixes with enzymes from the pancreas and bile juices from the liver for further digestion of protein, fat, and carbohydrates.

digestion5After the chyme gets fully digested, it gets absorbed into the blood through the wall of the intestine.  About 95% of absorption of nutrients occurs in the small intestine.  Therefore with diseases such as celiac disease and small bowel bacterial overgrowth, people commonly have nutritional deficiencies.


Once the digested food passes through the small intestine, it empties into the colon, where it becomes more concentrated into formed stool.  The stool travels through the colon through a process called peristalsis and eventually comes out upon defecation through the rectum.  A lot of times people experience “slow transit constipation” where the stool travels too slowly through the colon.  Also, problems related to the rectum and the pelvic muscle could cause constipation due to inability to evacuate the stool out of the rectum.