Types and Functions of Digestive Enzymes

Digestive enzymes are substances secreted by the salivary glands and cells lining the stomach, pancreas, and small intestine to aid in the digestion of food.

They do this by splitting the large, complex molecules that make up proteins, carbohydrates, and fats (macronutrients) into smaller ones, allowing the nutrients from these foods to be easily absorbed into the bloodstream and carried throughout the body.

Digestive enzymes are released both in anticipation of eating, when we first smell and taste food, as well as throughout the digestive process. Some foods have naturally occurring digestive enzymes that contribute to the breakdown of certain specific nutrients.

Deficiencies in digestive enzymes are associated with a variety of health conditions, especially those that affect the pancreas as it secretes several key enzymes.

Often these deficiencies can be addressed with dietary changes, such as restricting certain foods or adding those with naturally occurring digestive enzymes, or by taking prescription or over-the-counter (OTC) enzyme supplements.

Types

Each of the many different digestive enzymes targets a specific nutrient, splitting it up into a form that can eventually be absorbed. The most significant digestive enzymes are:

Amylase

Amylase is essential for the digestion of carbohydrates. It breaks down starches into sugars. Amylase is secreted by both the salivary glands and the pancreas. The measurement of amylase levels in the blood is sometimes used as an aid in diagnosing various pancreas or other digestive tract diseases.

High levels of amylase in the blood may indicate a blocked or injured duct of the pancreas, pancreatic cancer, or acute pancreatitis, a sudden inflammation of the pancreas. Low levels may indicate chronic pancreatitis (ongoing inflammation of the pancreas) or liver disease.

Maltase

Maltase is secreted by the small intestine and is responsible for breaking down maltose (malt sugar) into glucose (simple sugar) that the body uses for energy.

During digestion, starch is partially transformed into maltose by amylases. The maltase then converts maltose into glucose that is either used immediately by the body or stored in the liver as glycogen for future use.

Lactase

Lactase (also called lactase-phlorizin hydrolase) is a type of enzyme that breaks down lactose, a sugar found in dairy products, into the simple sugars glucose and galactose.

Lactase is produced by cells known as enterocytes that line the intestinal tract. Lactose that is not absorbed undergoes fermentation by bacteria and can result in gas and intestinal upset.

Lipase

Lipase is responsible for the breakdown of fats into fatty acids and glycerol (simple sugar alcohol). It's produced in small amounts by your mouth and stomach, and in larger amounts by your pancreas.

Proteases

Also called peptidases, proteolytic enzymes, or proteinases, these digestive enzymes break down proteins into amino acids. In addition, they play a role in numerous body processes, including cell division, blood clotting, and immune function.

Proteases are produced in the stomach and pancreas. The main ones are:

• Pepsin: Pepsin is secreted by the stomach to break down proteins into peptides, or smaller groupings of amino acids, that are either absorbed or broken down further in the small intestine
• Trypsin: Trypsin forms when an enzyme secreted by the pancreas is activated by an enzyme in the small intestine. Trypsin then activates additional pancreatic enzymes, such as carboxypeptidase and chymotrypsin, to assist in breaking down peptides.
• Chymotrypsin: This enzyme breaks down peptides into free amino acids that can be absorbed by the intestinal wall.
• Carboxypeptidase A: Secreted by the pancreas, it splits peptides into individual amino acids.
• Carboxypeptidase B: Secreted by the pancreas, it breaks down basic amino acids.

Sucrase

Sucrase is secreted by the small intestine where it breaks down sucrose into fructose and glucose, simpler sugars that the body can absorb. Sucrase is found along the intestinal villi, tiny hair-like projections that line the intestine and shuttle nutrients into the bloodstream.

Deficiencies

There are a variety of health conditions that can interfere with the secretion of sufficient amounts of digestive enzymes for the full digestion of foods. Some are inherited genetic conditions while others develop over time.

Lactose Intolerance

Lactose intolerance is the inability to digest lactose due to insufficient production of lactase by the small intestine. It is characterized by symptoms such as bloating, diarrhea, abdominal pain, and gas that result from consuming milk and other dairy products. There are several forms of lactose intolerance.

Congenital Lactase Deficiency

Congenital lactase deficiency (also called congenital alactasia) is a rare inherited form of lactose intolerance in which infants are unable to break down lactose in breast milk or formula and have severe diarrhea if they aren't given a lactose-free alternative.

Congenital lactase deficiency is caused by mutations in the LCT gene that provides instructions for making the lactase enzyme.

Lactase Non-persistence

Lactase non-persistence is a common type of adult-onset lactose intolerance affecting around 65% of adults. It is caused by decreased expression (activity) of the LCT gene. Symptoms typically begin 30 minutes to two hours after ingesting dairy.

Most people with lactase non-persistence retain some lactase activity and can continue to include some lactose in their diets, such as in the form of cheese or yogurt that tend to be tolerated better than fresh milk.

Secondary Lactose Intolerance

Secondary lactose intolerance develops when lactase production is reduced because of diseases that can cause damage to the small intestine, such as celiac disease or Crohn's disease, or from other illnesses or injuries that impact the intestinal wall.

Exocrine Pancreatic Insufficiency

The pancreas produces the key digestive enzymes of amylase, protease, and lipase. People with exocrine pancreatic insufficiency (EPI) have a deficiency of these enzymes and so are unable to digest food properly, especially fats.

The health conditions that affect the pancreas and are associated with EPI are:

• Chronic pancreatitis: An inflammation of the pancreas that can permanently damage the organ over time
• Cystic fibrosis: An inherited genetic condition that causes severe damage to the lungs and digestive system, including the pancreas
• Pancreatic cancer

Supplementation

People with health conditions that interfere with the secretion of sufficient amounts of digestive enzymes and those looking to support healthy digestion, might benefit from supplementing their diets with naturally occurring enzymes in whole foods or nutritional supplements under the guidance of a doctor.

Foods

A variety of foods, especially tropical fruits and fermented vegetables, are naturally high in digestive enzymes that might speed up the digestion of certain nutrients. It's best to consume them raw since heat can lessen or destroy these plant enzymes.

Nutritional Supplements

Digestive enzyme supplements can come in pills, powders, or liquids sourced from animals, plants, or microbes. There are prescription supplements regulated by the Food and Drug Administration (FDA) as well as OTC supplements.

Prescription enzyme supplements are indicated for conditions that affect the functioning of the pancreas, such as chronic pancreatitis or pancreatic cancer. Brands of prescription pancreatic enzyme supplements (pancrelipase) include Creon, Pancreaze, Zenpep, Ultresa, Viokace, and Pertzye.

Over-the-counter enzyme supplements are not regulated by the FDA. High-quality studies are lacking, so it is hard to know how effective they are. Among supplemental enzymes that don't require a prescription are:

• Lactase supplements may help people who are lactose intolerant to digest dairy products. They're available as tablets or drops.
• Bromelain, a powerful protease from the fruit or stem of pineapples, comes in capsule, tablet, or powder form and may aid with digestion of protein.
• Papain from papaya may help with digesting proteins and the powder form can be used as a meat tenderizer.

As with any supplement, check with your doctor before taking an OTC digestive enzyme to make sure it's safe for you.