The chemistry behind digestion and nutrient absorption

The process of digestion and nutrient absorption is a complex chain of events that starts from the moment food enters our mouth. The bite of food that we take triggers a series of chemical reactions that occur in the body, breaking down food into smaller molecules that can be absorbed by the body. This article delves into the chemistry behind digestion and nutrient absorption and aims to provide a comprehensive understanding of the science behind this crucial bodily function.

The Mouth

Digestion begins in the mouth where food is ground and chewed, helping to break it down into smaller pieces. The process of chewing also stimulates the release of an enzyme called amylase in the saliva. Amylase breaks down carbohydrates into simpler sugars like glucose. Once food is formulated into a small ball called a bolus, it is then ready to be swallowed and further broken down in the digestive tract.

The Stomach

Once food is swallowed, it enters the stomach where it mixes with digestive juices containing hydrochloric acid and pepsin. Hydrochloric acid helps to break down the proteins in food while pepsin digests them. The stomach muscles then churn the food until it forms a thick liquid called chyme.

The Small Intestine

The chyme then enters the small intestine where most of the nutrients from food are absorbed. The small intestine is lined with structures called villi, which are small finger-like structures that act as absorptive surfaces. The villi are lined with microscopic blood vessels and lymphatic vessels that transport nutrients and oxygen to the rest of the body.

The Liver and Pancreas

The liver and pancreas contribute to the digestive process by supplying additional enzymes and bile into the digestive tract. Bile, which is produced by the liver, helps to break down fats while enzymes produced by the pancreas help to further digest proteins, carbohydrates, and fats.

Absorption of Nutrients

Nutrient absorption occurs in the microvilli, which are even smaller structures that are found on the surface of the villi. The microvilli contain digestive enzymes and transport proteins that help absorb nutrients from the food. These nutrients are transported to different parts of the body via the bloodstream.

Carbohydrate Absorption

Carbohydrates are absorbed as simple sugars such as glucose, galactose, and fructose. These sugars are transported to the liver where they either get stored or used to produce energy.

Protein Absorption

Proteins are broken down into amino acids which are then transported to different parts of the body via the bloodstream. These amino acids are then used to build and repair tissues in the body.

Fat Absorption

Fats are broken down into smaller molecules called fatty acids and glycerol. These molecules are then absorbed by the villi and transported to the liver where they are used to produce energy or stored for future use.


The process of digestion and nutrient absorption is a complex and crucial bodily process that provides the body with the necessary nutrients to function properly. Understanding the chemistry behind this process helps us to make better dietary choices and take care of our bodies. The complex chain of events that take place during digestion and nutrient absorption highlight our body's ability to adapt and function at a microscopic level. Proper care and attention given to our digestive tract go a long way in ensuring that our body functions optimally and efficiently.