Because they are capable of digesting food before the body's own digestive process begins.
Lipase for digestion of fats, amylase and other enzymes for the digestion of complex carbohydrates and the secretion of hydrochloric acid are all necessary for the digestion in humans of our foods which hold the nutrients.  Each enzyme is specific to a particular compound, which it can break down or synthesize. The three most important enzymes for digestion are protease, amylase, and lipase. They digest protein, carbohydrate, and fat, respectively. Digestive enzymes are produced internally and deal with the digestion of food and the absorption and delivery of nutrients throughout the body. The most commonly known digestive enzymes are secreted from the pancreas into the stomach and small intestine. Digestive enzymes are energized protein molecules. They are extremely vital for digesting food and maintaining a healthy body. Enzymes play a catalytic role in the action pathways of the human body. They are essential for normal hormone production, action and metabolism. There are also a number of other enzymes that are required for the proper functioning of the digestive system. For example, there are digestive enzymes like lactase, cellulase and sucrose. Lactase helps in the digestion of dairy products and lactose. 95% of your food is composed of carbohydrates, proteins and fats. Digestive enzymes are composed of various amounts of amylase, protease and lipase. Amylase helps in digesting carbohydrates, protease helps in digesting proteins and the lipase helps in digesting fats. These three enzymes play a crucial role. There are also a number of other enzymes that are required for the proper functioning of the digestive system. For example, there are digestive enzymes like lactase, cellulase and sucrose. Lactase helps in the digestion of dairy products and lactose. Cellulase helps in fiber digestion, while sucrase helps in the digestion of starches and sugars. Without digestive enzymes, your body wouldn't be able to digest and breakdown the food it ingests if we didn't have enzymes as part of our digestive system, digestion would take a lot longer. Enzymes break food down into smaller pieces after mechanical digestion so that chemical digestion can work on smaller pieces of food. different types of enzymes break down different types of food substances. Amylase breaks down starches into simple sugars Our bodies make digestive enzymes as well, mainly in the pancreas, the stomach, the small intestine, and the mouth. There are 22 known digestive enzymes with names that end on-ase such as: ~ Amylase (digests carbohydrates); ~ Lipase (digests fats); ~ Protease (digests proteins); ~ Disaccharides (digest sugars). Enzymes are special proteins. They are essential for every chemical reaction in the body and for the normal activity of the cells, tissues, fluids, and organs. Vitamins, minerals, hormones, and all the food we eat can do nothing without enzymes. Is the pancreas important to the digestive system? The pancreas secretes important digestive enzymes (pancreatic amylase, pancreatic lipase, trypsin, and chymotrypsin) which empty into the duodenum (first part of the small int … estine) to break down the carbohydrates, fats, and proteins we ingest.  Plant enzymes are important because they are capable of digesting food before the body's own digestive process begins. In other words, plant enzymes can enhance the digestion of food and the delivery of nutrients to the blood even if you have a compromised digestive system. The same cannot be said of animal enzymes such as pancreatin. Everyone agrees that proper nutrition is crucial to the maintenance of a healthy body. Digestive enzymes also help break down the supplements we take so that the vitamins, minerals and other nutrients we supplement with can be used effectively and not wasted. Digestive enzymes help ensure digestion of our food and supplements. Partial digestion of our meals can cause harmful imbalances in our body.  The body can make digestive enzymes; however, the more digestive enzymes required for digestion, the fewer enzymes it can create to maintain optimal health. It is very important that we preserve the body’s ability to make enzymes. If digestive enzymes supplements are taken with a meal, these digestive enzymes begin their work immediately. The supplemental digestive enzymes will break down the food, thus saving the body from having to release as many of its own enzymes.
http://www.wayoflifematters.com/digestion-in-humans.html http://www.perfecthealthnow.com.au/bioset/what-is-bioset/enzymes-information-and-function/enzyme-information/ http://www.aboutgastro.com/news/digestive-enzymes-important-digestion http://www.aboutgastro.com/news/digestive-enzymes-important-digestion http://www.answers.com/Q/Why_are_enzyme_important_in_digestion http://www.yogalifestylecoach.com/enzymes.html http://www.answers.com/Q/Why_are_enzymes_important_for_digestive_system http://www.naturalenzymes.com/learnmore/why-food-enzymes-are-important.aspx http://alleganynutrition.com/index.php?Why%20digestive%20enzymes%20important http://www.enzymeessentials.com/HTML/enzyme_index.html
why are enzymes important in digestion