What is chemical digestion?

When it comes to digestion, chewing is only half the battle. As food travels from your mouth into your digestive system, it’s broken down by digestive enzymes that turn it into smaller nutrients that your body can easily absorb.

This breakdown is known as chemical digestion. Without it, your body wouldn’t be able to absorb nutrients from the foods you eat.

Read on to learn more about chemical digestion, including how it’s different from mechanical digestion.

Chemical and mechanical digestion are the two methods your body uses to break down foods. Mechanical digestion involves physical movement to make foods smaller. Chemical digestion uses enzymes to break down food.

Mechanical digestion

Mechanical digestion begins in your mouth with chewing, then moves to churning in the stomach and segmentation in the small intestine. Peristalsis is also part of mechanical digestion. This refers to involuntary contractions and relaxations of the muscles of your esophagus, stomach, and intestines to break down food and move it through your digestive system.

Chemical digestion

Chemical digestion involves the secretions of enzymes throughout your digestive tract. These enzymes break the chemical bonds that hold food particles together. This allows food to be broken down into small, digestible parts.

How they work together

Once food particles reach your small intestine, the intestines continue to move. This helps keep food particles moving and exposes more of them to digestive enzymes. These movements also help to move the digested food toward the large intestine for eventual excretion.

Digestion involves taking large portions of food and breaking them down into micronutrients small enough to be absorbed by cells. Chewing and peristalsis help with this, but they don’t make particles small enough. That’s where chemical digestion comes in.

Chemical digestion breaks down different nutrients, such as proteins, carbohydrates, and fats, into even smaller parts:

  • Fats break down into fatty acids and monoglycerides.
  • Nucleic acids break down into nucleotides.
  • Polysaccharides, or carbohydrate sugars, break down into monosaccharides.
  • Proteins break down into amino acids.

Without chemical digestion, your body wouldn’t be able to absorb nutrients, leading to vitamin deficiencies and malnutrition.

Some people may lack certain enzymes used in chemical digestion. For example, people with lactose intolerance usually don’t make enough lactase, the enzyme responsible for breaking down lactose, a protein found in milk.

Chemical digestion begins in your mouth. As you chew, your salivary glands release saliva into your mouth. The saliva contains digestive enzymes that start off the process of chemical digestion.

Digestive enzymes found in the mouth include:

  • Lingual lipase. This enzyme breaks down triglycerides, a kind of fat.
  • Salivary amylase. This enzyme breaks down polysaccharides, a complex sugar that’s a carbohydrate.

Chemical digestion doesn’t just stop with enzymes in your mouth.

Here’s a look at some of the main stops on the digestive system involving chemical digestion:


In your stomach, unique chief cells secrete digestive enzymes. One is pepsin, which breaks down proteins. Another is gastric lipase, which breaks down triglycerides. In your stomach, your body absorbs fat-soluble substances, such as aspirin and alcohol.

Small intestine

The small intestine is a major site for chemical digestion and absorption of key food components, such as amino acids, peptides, and glucose for energy. There are lots of enzymes released in the small intestine and from the nearby pancreas for digestion. These include lactase to digest lactose and sucrase to digest sucrose, or sugar.

Large intestine

The large intestine doesn’t release digestive enzymes, but it does contain bacteria that further break down nutrients. It also absorbs vitamins, minerals, and water.

Chemical digestion is a vital part of the digestive process. Without it, your body wouldn’t be able to absorb nutrients from the foods you eat. While mechanical digestion involves physical movements, such as chewing and muscle contractions, chemical digestion uses enzymes to break down food.