There are enzymes everywhere in your body, but each one has to perform the task set out for it. Different enzymes work in different forms, at different speeds and with different substrates, which accounts for their variety.
Enzymes are generally classified according to the basic functions they perform. Enzymes that maintain the body's entire metabolism, from the respiratory system to the nervous system, are known as metabolic enzymes. Those groups known as food enzymes are those we absorb together with the foods we eat. The third enzyme group is known as digestive enzymes.

Metabolic Enzymes

Foodstuffs are broken down and digested, following which countless metabolic processes take place. Metabolism is the name given to the magnificent phenomena taking place in an organism's cells and controlled by enzymes, which direct every metabolic process in the body, bringing about energy and substance production.
ATP production and protein synthesis are two major metabolic reactions. Metabolic enzymes are responsible for taking over and performing all these processes.

With the exception of reproductive cells—which represent only 0.1% of the body's weight—your body is completely different from what it was 12 years before. Over those dozen years, all the cells in your body have been renewed. Your liver is not the liver it once was. In the same way that the blood cells in your circulatory system are not the same ones that existed 10 years ago, neither are the veins through which they flow. Your organs have completely changed and have been renewed, with entirely new cells and molecules. This is of course an astonishing phenomenon.

The most rapid renewal takes place in the epidermis. Every three months, you are given a new skin. The rest of your organs then follow. Over the years, your lungs, kidneys, stomach and all your other organs change—even your eyes that now read these lines. The slowest changes take place in the bone and cartilage. It takes some 10 years for them to change—yet these, too, are finally renewed.

For that reason, there is a constant need for construction in the body. And of the workers engaged in the construction of your body, the most important are the metabolic enzymes. They take in 45 essential nutrients, and convert them into muscles, nerves, bones, blood and organs. At a basic level, they provide the fuel that keeps the cells alive. They enter all the reactions essential for the cell to fulfill its own functions and finish them in a very short space of time. They operate in all vital matters, such as the DNA replication, ATP energy storage, nutrient entry into cells and waste products' exits, and the transmission of electrical signals along the nerves from your sense organs.

Metabolic enzymes are a treasure bestowed on us from the moment we are born. Like construction workers in our bodies, they take 45 essential nutrients and convert them into muscles, bones, nerves and organs. In fact, however, enzymes are simply tools. It is our Lord Allah, the Creator of all things, Who supplies all the countless means by which we are kept alive.

Metabolic enzymes are a great blessing bestowed on us by our Lord, important treasuries we enjoy from the moment we are born. They are at work from the moment our lives begin, ready to perform countless functions. These same enzymes will repeat the same tasks time and time again, never stopping. Yet they also have their own life spans. Enzymes decline in number as we grow older. "Old age" is another term for the decrease in the number of enzymes in the body, and therefore they are unable to function as efficiently as before. Old age is actually an indication not of how much a person has lived, but whether or not the tissues in the body are fully functioning. These tissues depend on the level of enzymes charged with the metabolism of every cell. In other words, the more numerous and functional the enzymes, the more youthful a person's metabolism.56

Of course, the functioning of all these systems and the maintenance of this metabolic order are totally beyond your control. Even if people are young and enjoy a balanced diet, there is nothing they can do to keep their bodies alive if their enzymes do not perform the requisite functions. Cells will continue to die, but will not be renewed, and the organs will increasingly lose their capacity to function. Enzymes are entities that keep one alive. However, do not forget that enzymes are all proteins with no intelligence or consciousness. What we refer to as "metabolism" is nothing more than the functioning of these proteins. There is no point in your trusting in these entities to keep you alive, and it is totally irrational to think that these entities were charged with keeping people alive by chance. We need to realize that it is Allah Who keeps human beings alive. Allah has created all the systems belonging to a human, inspires them to carry out their functions at every moment, creates them at every moment and keeps them under His control at all times.

If a system of yours is interrupted, all you can do is to take the necessary precautions, turn to Allah and seek His assistance. It is Allah, Who keeps you alive, Who will help you. Allah has revealed this in a verse:
Allah is He to Whom the kingdom of the heavens and earth belongs. He gives life and causes to die. You have no protector or helper besides Allah. (Surat at-Tawba: 116)

Food Enzymes

Every bite you eat contains important building blocks to be used in the construction of your body. Food that you eat enters with an even more important factor that helps digest the food itself: its own enzymes.
Food enzymes are present in every food we can encounter anywhere on Earth, but they are not resistant to heat. When you cook food, you lose all the enzymes it contains. However, if you eat a raw food, its own enzymes will digest 75% of it. Digestion of any food by its own enzymes makes a very important contribution to the body, since your system need not become fatigued by manufacturing extra enzymes, and it has no need to slow down the production of metabolic enzymes, so essential to the cells, in order to produce digestive enzymes.
Excellent examples of the enzymes constantly active in foods are those present in fruit. In its green state, a banana is 20% starch. When left in a warm place for a while, however, the enzyme amylase converts that 20% starch to 20% sugar. Around a quarter of that sugar is glucose, which the body now has no need to digest.57

Thanks to the enzymes it possesses, fruit completes a major task that is usually carried out in the body before it's even consumed.

Like the banana cited in this example, every fruit or vegetable eaten without being cooked conveys various nutritional benefits without putting the body to any trouble. When you eat a banana, its own enzymes offer it already prepared for your cells by breaking it down—together with the digestion process that begins in the mouth—into small components that can be utilized by your metabolic enzymes, which then assimilate them into the body by converting them into the structural materials needed for cells and organelles.

The enzymes concealed in foodstuffs are able to digest only the particular food in question. For example, the amylase in bananas works only on the banana starch. This enzyme cannot digest the starch in a potato. After you eat a banana, enzymes in the banana cannot help you digest a slice of cooked meat. Nor can these enzymes add any extra enzymes to the body. Their task comes to an end with the digestion of the food in question. An enzyme that enters the body along with food recognizes the food it is going to digest, despite its being broken up in the mouth, and sets itself to digesting it. Given these properties, enzyme molecules literally behave with intelligence. Of course an inanimate molecule cannot really exhibit intelligence—the wisdom we see in the functions that enzymes perform actually belongs to Almighty Allah, Who creates them and places them at the service of living things.

When you eat a cooked food that has lost all its enzymes, the whole job of digestion falls to those enzymes at the ready in your body. The digestive organs, the pancreas in particular, go into extreme production mode to ensure the digestion of food that has entered the stomach by producing large quantities of enzymes. And this production may cause the production rate of metabolic enzymes to fall. This means that insufficient production can be made for the organs to function, renew themselves, and fight disease. Thus the body expends on digesting foods the energy it should use for its own development and defenses. One of the first researchers into the importance of enzymes in human nutrition, Dr. Edward Howell, founder of the National Enzyme Company, has said this:

They are the most precious asset we possess and we should welcome outside enzyme help. If we depend solely upon the enzymes we inherit, they will be used up just like inherited money that is not supplemented by a steady income.58

By endowing foods with enzymes, Allah has bestowed a most important blessing on us. The way that these enzymes know what they must do as soon as they enter the body, adapt to a mechanism that is completely foreign to them and immediately begin to process the food they need to digest is literally miraculous. These enzymes literally behave in a conscious manner and know that they should go into action the moment the food is broken down. They neither destroy it by acting prematurely, nor go into action hours after it has entered the mouth. They begin working at just the right moment and conclude the whole enterprise at great speed. With the help of these molecules, every fruit you eat is turned into building blocks with which the body can renew itself. Thus it is that your eyes continue to see, your legs to move and your organs to function.

Remember, these unconscious molecules are entities created by Allah and never go wrong because they act under His direction. They act under the infinite intelligence of Allah and have bowed their heads to Him. Allah tells us of this in another verse:

[Hud said,] "I have put my trust in Allah, my Lord and your Lord. There is no creature He does not hold by the forelock. My Lord is on a Straight Path." (Surah Hud: 56)

Digestive Enzymes

Certain enzymes have been charged with digestion in the body. Lipase breaks down fats, protease breaks down proteins, cellulase breaks down fiber, amylase breaks down starch, lactase breaks down dairy, sucrase breaks down sugars, and maltase breaks down grains. The presence of digestive enzymes is of great importance to metabolic enzymes, because digestion being undertaken by a special enzyme group prevents the metabolism from fatigue. As long as digestive enzymes are present, our bodies' metabolic enzymes can carry out their own tasks alone and need not become involved in such a complex and detailed process as digestion.

For that reason a glorious mechanism operates constantly inside the human body. Whenever you see or smell something to eat, or even if you only think about it, your body triggers the production of digestive enzymes. These stimuli are of great importance, helping ready your body to deal with food before you have even taken a bite.

Enzymes break down foodstuffs and convert them into forms that the body's cells can use. This perfect system enables all the system's needs to be met almost instantaneously.

This diagram shows the activity of the enzyme sucrase in breaking down sugar products. The new product emerging as a result of this reaction will be used in meeting the needs essential to the body's metabolism.

The process of digestion begins in the mouth, immediately after the food has been chewed. Saliva contains special enzymes, and as soon as they come into contact with food, they start breaking it down. We break down the exterior walls of foods through the chewing process. If the food is raw, the enzymes it contains are released and initiate the digestion process. Carbohydrates begin to be digested in the mouth, when the amylase in saliva breaks the molecular bonds in starch and adds to them the water molecules in saliva. The reason why you feel an increasingly sweet taste when you chew a piece of bread is that the enzymes in your saliva are converting the starch it contains into sugar. For digestion in the mouth to take place, the necessary pH value is between 6.0 and 7.4, and the enzyme amylase functions best in that pH range. The stomach, on the other hand, is a highly acidic environment, with a pH level of between 1.0 and 3.5—which acidic conditions halt the activity of amylase. For that reason, carbohydrate digestion does not take place in the stomach. The process of digestion begins in the mouth, then continues in the stomach and the intestines, all of which are rather different from one another in their working conditions. They therefore harbor appropriately different enzymes.

Special Enzymes in the Stomach

Along the digestive route that starts with the mouth, the next major station is the stomach. As with all organs, the stomach contains enzymes that perform special functions. Their very presence in the rather harsh environment of the stomach, which dissolves and breaks down everything that enters it, is of course very surprising. Yet in any case these assistants are specially equipped for working in the stomach, and are another part of this great miracle inside the body.

The stomach is a highly acidic environment, whose walls need to be protected against its own acid. The digestive enzymes also need to be able to survive within it. The stomach meets both conditions. The internal lining of the stomach wall, covered in a mucous layer that comes into contact with food, contains three kinds of cells. One of these secretes hydrochloric acid (HCl), a very powerful acidic solution, strong enough even to dissolve stone. This powerful chemical also plays an important part in the digestive process by breaking down all proteins, particularly meat, entering the stomach, and kills all microbes. Another important characteristic of this acid is that it sets into action pepsinogen, also present in the stomach and which breaks down proteins. Pepsinogen is not secreted when the stomach is empty. Yet when any food reaches the stomach, pepsinogen is converted into the enzyme pepsin by an activator protein, literally as if someone had told it to, and breaks down the foodstuff there.

The anatomy of the stomach and the production of pepsinogen by the chief cells in the stomach. This production takes place as follows: The chief cells manufacture molecules such as pepsinogen, which are converted into the enzyme pepsin by activator enzymes. Parietal cells secrete HCl (hydrochloric acid) that activates the chief cells. It is totally illogical to imagine that such a system with its interdependent and exceedingly complex processes could have come into being by chance.

How can we account for the way that pepsin initiates digestion by recognizing a piece of meat consisting of protein and fats, but does no harm to the stomach, which consists of basically the same protein and fats? Again, how are we to explain the way that hydrochloric acid does not dissolve the stomach itself and the helper enzyme? It is impossible under normal conditions for an enzyme, an acid, molecules, messenger hormones or even the stomach itself to recognize acid's dangers, or the foods that need to be digested, and to take the relevant precautionary measures on a constant, error-free basis at specific times of day. It is Allah Who makes this possible, ensuring that these processes take place uninterruptedly inside all the humans living on Earth, and Who ensures that the molecules receive their instructions, obey them and are compatible with one another.

It is impossible for a molecule to be aware of another molecule by chance, for it to activate by chance, to be aware of dangers by chance and to take appropriate precautionary measures. Each one of these complex structures, literally in communication with one another, cannot have emerged "out of nothing" by chance, nor have been assembled by means of a chain of unconscious events and begun their functions, again by chance. Anyone of reason and good conscience, who reflects honestly and is not unmoved by what he sees and knows, will immediately appreciate this obvious fact. The boundless nature of the blessings imparted by Allah is revealed in a verse:
Is He Who creates like him who does not create? So will you not pay heed? If you tried to number Allah's blessings, you could never count them. Allah is Ever-Forgiving, Most Merciful. (Surat an-Nahl: 17-18)

Even more striking details are contained within the stomach's digestive processes. The stomach is lined with a perfect protective material. The sensitive goblet cells secrete this protective mucus, which works just like a protective layer, even before the acid and breaking-down enzymes are emitted. Despite this protective substance's extraordinary strength, the stomach still loses 1.5 million cells a day to the effects of acid and enzymes. The entire internal lining of the stomach is destroyed, but then renewed, every three days.

The stomach might not have always renewed these naturally dying cells. This system is so tightly controlled that you are totally unaware of its ongoing intervention. New cells are always produced to replace those that die. Both the destruction of old cells and the production of new ones take place at Allah's choosing.

Ulcers are a reminder of the consequences of the absence of such a system. The disorder involves a failure to secrete protective mucus for one reason or another. Acid and enzymes begin damaging the stomach wall and blood begins leaking from the blood vessels beneath. The stomach wall now has an open sore. Until treated, the stomach's own secretions will continue to kill the stomach cells, and foodstuffs will not be digested.

Following the release of protective mucus in the stomach, food reaches the upper portion of the stomach for digestion. No enzymes are secreted here. Raw food goes into this section of the stomach. After swallowing, digestion continues here with these food's own enzymes for half an hour to an hour. After that, pepsin, the stomach enzyme, takes over.

If the food has been cooked, it waits in this section of the stomach for half an hour to an hour, with no enzymes breaking it down. Salivary enzyme breaks down carbohydrates, but protein and fat have to wait. These foods are subjected to a different process in the stomach than raw foods which already contain enzymes, because the body's metabolism must devote its attention to supplying more metabolic enzymes for the organs and tissues. In other words, another conscious choice is made inside the body. After being kept in this stomach region for a while, the food will start being broken down by gastric enzymes.59

The process of acid secretion in the stomach is controlled by the presence of food. In response to food's presence in the stomach, specific cells go into action, secreting a hormone known as gastrin into the bloodstream. It then emits a signal to the glands that secrete hydrochloric acid and thus stimulates secretion of gastric juice.

The nervous system also has a role in the secretion of gastric juice, because the glands responsible are under the control of the nervous system. So, the release of digestive fluids is controlled by both hormones and by the nervous system, which is why increased stress and high blood pressure may lead to the formation of ulcers. Indeed, that it is enough that we smell, taste or even think of food for the brain to send messages to the secretory glands in the stomach demonstrates the efficiency of the nervous system in the digestive process.60

Pepsin is the active enzyme that breaks down proteins in the stomach. The stomach wall cells produce this enzyme in an inactive form, known as pepsinogen. As already mentioned, hydrochloric acid converts pepsinogen into pepsin. The secretion of pepsinogen by the gastric secretory glands is at the same time controlled by the activities of the hormone gastrin. The presence of food in the stomach, the secretion of gastrin, the production of hydrochloric acid and the conversion of pepsinogen into pepsin are all interconnected. Therefore, the entry of food into the stomach initiates a chain of highly complex stages.

Pepsin converts large protein molecules into small polypeptides, but each polypeptide molecule contains a large number of interconnected amino acids. The breaking down of these continues in the small intestine.61

There is a gate where the stomach opens into the intestine, whose presence is of great importance, because if the stomach were not separated from the intestine, it would entail the possibility of foods in the intestine being returned to the stomach, which would have a damaging impact on the stomach's own acidic environment. Enzymes in the intestine operate in a more neutral and alkaline environment, and these special enzymes would be impaired by the stomach's acidity and give rise to dangerous consequences.62

Digestive enzymes have similar structures and functions, yet those that function in the intestine cannot adapt to the gastric environment, nor vice versa. This shows that every region, every tissue and every organ in the body is created with different properties; and that enzymes have also been equipped with features appropriate to the conditions in these separate environments.