Protein Digestion: A Process Of 4 Steps



Published on: 08-Feb-2023


10 min read


Updated on : 02-Dec-2023




Harsimran Kaur


Protein Digestion: A Process Of 4 Steps

Protein Digestion: A Process Of 4 Steps

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While we consume proteins for lean muscles and healthy bodies, do you know how digestion occurs in your body?

Like human personality, the human body is also complex. While from the outside, eating food seems easy, inside, a lot is going on with that dish you just ate for digestion. 

To put that inside process into scientific terms, the act of breaking down food molecules into smaller components is digestion. This procedure starts in the mouth and progresses to the stomach, small intestine, large intestine, and finally, the anus.  When you consume anything, your body's digestive system breaks it down into individual amino acids, which are absorbed and utilised by cells to produce more proteins and a few other macromolecules like DNA. 

Though protein benefits health, overconsumption can lead to various medical conditions like diabetes, cancer, and osteoporosis. So, while consuming food, ensure you intake a suitable amount of protein that your body can smoothly digest without causing side effects. In this blog, let us trace the precise journey of proteins through the digestive tract and into the circulatory system. Let us understand more about the chemical process of digestion that occurs when you digest molecules.

Table Of Contents

1. What Is Protein?

2. Enzymes Involved In Protein Digestion

3. How Is Protein Digested?

4. Dietitian’s Recommendation

5. The Final Say

6. FAQs

What Is Protein?

Protein is the most vital substance in the human body and the primary component of muscles, hair, eyes, organs, and numerous hormones and enzymes. It helps in healing and maintaining your body's tissues, apart from aiding in weight loss.

Protein is a nutrient made up of smaller molecules known as amino acids. Though there are 20 amino acids, your body is capable of producing only 11. The remaining nine are essential amino acids, as you can get them only from food.

All remaining nine vital amino acids are present in high-quality protein sources like meat, fish, egg, and dairy products. These are also known as complete proteins due to their composition.

Other protein sources, like nuts, beans, and seeds, only provide limited essential amino acids. However, many of these protein sources, like rice and beans, may be combined to provide a complete protein that includes all nine crucial amino acids.

Enzymes Involved In Protein Digestion

Protein digestion occurs when you start chewing. Amylase and lipase are the enzymes found in saliva that vitally degrade carbs and lipids. When a protein source reaches your stomach, it breaks down into smaller chains of amino acids by hydrochloric acid and proteases. Peptides connect amino acids, which proteases disintegrate.

These smaller chains of amino acids pass from your stomach and enter your small intestine. Here, your pancreas responds by releasing enzymes and a bicarbonate buffer, decreasing the acidity of digested food. This decrease frees up additional enzymes to concentrate on breaking down amino acid chains into individual amino acids. Some common enzymes involved in this process are:

  • Trypsin
  • Chymotrypsin
  • Carboxypeptidase
  • Pepsin

How Is Protein Digested?

How Is Protein Digested

Digesting protein is not a simple process, as it involves the following complex steps:

1. Digestion Of Proteins In The Mouth

Chewing is the first step of digestion. Here, the food items are broken down into smaller bites you can eat with your teeth. The salivary glands produce saliva to help swallow and move partly mashed food through the oesophagus.

2. Digestion Of Proteins In The Stomach

From the oesophagus, the mashed food bites enter the stomach, where mechanical and chemical digestion occurs. In this step, your stomach releases the gastric fluids comprising hydrochloric acid and pepsin to start the chemical breakdown of protein. 

Here, peristalsis, or muscular contractions, also contribute to digestion. The forceful contractions of the stomach churn the partly digested protein into a more homogeneous substance known as chyme.

During this, food proteins denature due to stomach acidity, unravelling their three-dimensional structure to show only the polypeptide chain. It is the first stage of protein chemical digestion. 

When proteins denature in the stomach, the peptide bonds that connect amino acids become more accessible to enzymatic digestion. Pepsin, an enzyme released by the cells lining the stomach and activated by hydrochloric acid, initiates this process. It starts breaking down peptide bonds, resulting in shorter polypeptides.

Protein digestion takes more time in the stomach than carbohydrate digestion but less than fat digestion. Eating a high-protein meal increases the time needed to break down the food in the stomach, which stays there for longer, making you feel fuller for hours.

3. Protein Absorption And Digestion In The Small Intestine

By this time, chyme is ready to exit the stomach and enter the small intestine, where maximum protein digestion takes place. Here, the pancreas secretes digestive fluids into the small intestine, which includes additional enzymes for further polypeptide breakdown.

Chymotrypsin and trypsin are the two essential pancreatic enzymes that break down proteins in the small intestine. Trypsin stimulates other protein-digesting enzymes known as proteases. These enzymes break proteins into tripeptides, dipeptides, and individual amino acids. The cells lining the small intestine release additional enzymes, which assist in the enzymatic breakdown of polypeptides.

4. Protein Absorption And Digestion In The Large Intestine

Protein that the small intestine fails to digest passes into the large intestine, from where it leaves the body in the faeces. As some proteins are locked in plant cell walls, plant-based proteins are slightly less digestible than animal proteins.

And here, the protein digestion process ends to offer numerous benefits to your body for a healthy life.

Dietitian’s Recommendations

Protein is an essential food needed for numerous bodily activities. A person should eat complete proteins and practise a few things, like chewing the food properly before swallowing, to optimise the nutrients you obtain from protein sources.

- Dietitian Lavina Chauhan 

The Final Say

Protein is vital for practically every organ in your body. It starts processing in your mouth, stomach, small intestine, and large intestine before being released from your body. It has numerous health benefits you can enjoy with adequate daily consumption.


1. Where does protein digestion begin and end?

Mechanical digestion of protein initiates in the mouth and keeps working in the stomach and small intestine. The chemical digestion of protein starts in the tummy and ends in the small intestine.

2. Which enzymes help in protein digestion?

The two prominent pancreatic enzymes that help digest proteins are chymotrypsin and trypsin. The cells that line the small intestine release additional enzymes that disintegrate the smaller protein fragments into individual amino acids.

3. Where is protein digested first?

Proteins are first digested in the stomach by the action of pepsin, secreted by peptic or chief cells as proenzyme pepsinogen, by converting proteins into smaller polypeptides.

4. What is the end product of protein digestion?

After looking through the process of protein digestion, which starts in the mouth, the end product of this procedure is amino acids.

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