Digestive Enzymes

Dr. Anthony Cheung, F.R.C.P.(G)

Despite the rapid growth in Science, many people would like to go back to a more natural lifestyle. Nowadays, self-medication is becoming more popular and in actual fact it is a way of life, as pointed out by V. Chiles in the book, Canadian Self-Medication.(1) In the early 1900's, the importance of vitamins in health and disease was recognized. This was followed by an emphasis on the roles played by minerals and trace elements. Nutritionists were not entirely satisfied with just vitamins, minerals and trace elements as their only weapons to achieve the optimal health of human beings. They felt that there was a missing link somewhere. Their dream did not come true until about fifty years ago, when Dr. Edward Howell began his study of food enzymes and human health, and the missing link was then revealed. His enzyme philosophy, though not universally accepted by orthodox physicians and other health professionals, is shared by other well-known scientists like Drs. Loeb and Northrop of the Rockefeller Institute of Medicine, Professor R. Pearl of Johns Hopkins University, and Drs. MacArthur and Baille of the University of Toronto. Food enzymes are now considered "the third wave" in nutritional supplementation.

During the course of medical curriculum, digestive enzymes are taught in Physiology and again in Clinical Pharmacology. All medical doctors must have learned something about digestive enzymes during their academic years before they are qualified to practice. One may be surprised to hear Dr. E. Howell say "I do not think you will get many opinions from medical doctors about food enzymes because they do not like to say anything about a subject they do not understand," in his book Food Enzymes for Health and Longevity.(2) Because of this curiosity, i was motivated to research the topic of food enzymes.


According to the American Pocket Medical Dictionary, (Nineteenth Edition), "enzyme" is defined as an organic compound, frequently a protein, which is able to accelerate or to produce by catalytic action some change in a substrate for which it is often specific. Such a general definition is accepted by medical doctors as well as nutritionists and scientists who are interested in food enzymes. They agree that humans, animals and plants are composed of cells with different activities, both inside and outside the cell membrane. All these activities need the presence of enzymes in order to function. Without enzymes, there will be no cellular activities. A cell without cellular activities is considered dead. Enzymes, like vitamins and essential minerals, are vital to all living things. It is just like a car with an intact engine battery and a full tank of gasoline, but no engine oil. The car with such configuration cannot run if there is no engine oil for lubrication. The engine oil therefore, plays a similar important role in a functioning car as the enzymes contribute to the integrity of a living cell.

In man, we have different enzymes in different systems. Those that are concerned with digestion are known as digestive enzymes which are secreted by special glands or mucosal cells along the digestive pathway. Their chief function is to metabolize the ingested food so that its components can be absorbed and utilized by our body. This whole process of digestion, absorption and utilization is known as "assimilation".

Food enzymes are digestive enzymes present in food or food supplements. Their sources can be animal (eg. uncooked meat) or vegetable in origin. In medical terms, digestive enzymes secreted by our digestive system inside our body are "endogenous". Those taken as food or food supplements (food enzymes) are "exogenous". Some common characteristics of these digestive enzymes are:

  1. they function best at certain pH and temperature,
  2. they are easily destroyed by high temperature, such as cooking and food processing, and
  3. once destroyed, they must be replaced.


It is well known to all of us that our food is mainly composed of proteins, carbohydrates, fats, water, vitamins, minerals and trace elements. The exact mechanisms of their assimilation (digestion, absorption and utilization) are very complicated. For those who are interested in this topic, they are encouraged to look into the textbooks of physiology, biochemistry and pharmacology.(3) For the lay person, we classify the digestive enzymes into four main groups:

  1. the carbohydrase enzymes digest carbohydrates which might be simple monosaccharides (glucose, fructose and galactose), dissaccharides (sucrose, lactose and maltose) or complex polysaccharides (starch and fibres). The end products are monosaccharides.
  2. the protease enzymes digest proteins which are then broken down to proteoses, peptones, polypeptides, dipeptides and finally the end products, amino acids.
  3. the lipase enzymes digest fats, which are composed of neutral fat (triglycerides), phospholipids and cholesterols. The main end products of the digestion of fats are fatty acids and glycerides which are not water soluble. It is only with the aid of the bile acids that the majority of the fat is absorbed through the intestinal epithelial cells into the lymphatic system via the lacteals of the villi. About 10% of the fatty acids are absorbed into the portal blood and carried to the liver for further metabolism. Chylomicrons are small particles of fat formed in the blood during digestion of fat. They are covered with a protein coat which makes them hydrophilic (soluble), allowing a certain degree of suspension stability in the fluid medium (blood).
  4. the cellulase enzymes digest cellulose which is a complex carbohydrate forming the framework of plant structures (fibres). It plays no significant role in human beings and is not found in the endogenous secretion of the human digestive enzymes. It may be an essential enzyme in herbivorous animals.

It is often said that digestion begins in the oral cavity (mouth) where food is chewed before swallowing. Proper chewing (mastication) is essential because it will allow:

  1. the breakage of the undigestible cellulose coat around the nutrient portions of fruits and raw vegetables, and
  2. better mixing of the digestive enzymes (ptyaline, an amylase from salivary glands) with the food particles.

Actually, the process of digestion is triggered before we even taste our food with our tongue. The sight of seeing a well prepared meal, the smell of our favourite food or even the thought of tasting a delicious dish, will make our mouth water. The enzymes are all ready for their prey.

In the old days, the stomach was considered only as a store-house where mixing of the ingested food and gastric secretion (hydrochloric acid and digestive enzymes) occurred. The process was known as churning. The physiologists would rather consider the stomach to be functionally divided into two major parts:

FIGURE: Simple anatomy of the stomach.

  1. the upper part (the fundus and body) which is mainly concerned with the storage and mixing, and
  2. the lower part (the antrum and the pylorus). The strong peristaltic movements in the antral portion of the stomach coupled with a narrow opening of the pylorus will create a better mixing or churning of the ingested food and gastric secretions. The resulting mixture of the gastric contents is known as "chyme" which has an appearance of a murky or milky semi-fluid substance.

The chyme is gradually emptied into the small intestine for further digestion and absorption. There are two sequences initiated as the stomach empties: 

  1. the neurological sequence (the distension of the stomach by food will send signals via the nerves to the body's headquarters, the brain, which will then send orders through the nervous pathway to do the appropriate things) and
  2. the hormonal sequence (the presence of food in the stomach also stimulates the release of a hormone known as gastrin from the antral mucosa. The gastrin in turn will control not only the secretion of highly acidic gastric juice by the gastric glands, but also the emptying of the stomach by enhancing the activity of the pyloric pump and simultaneously relaxing the outlet, the pylorus).

Before we move any further, we can summarize the functions of the stomach as follows:

  1. The upper part acts as a store-house where partial digestion of food is being initiated.
  2. It secretes gastrin, hydrochloric acid and other enzymes which function best in an acidic environment.
  3. Churning of food occurs in the lower part of the stomach, the antrum. The chyme so formed is emptied into the small intestine by the "pyloric pump" which is regulated by nervous and hormonal mechanisms.

When the chyme reaches the upper part of small intestine, the whole process of digestion and absorption is much more complicated. But as I have emphasized before, I do not intend to go into details.

In a nutshell, the partially digested food from the stomach will be broken down to end products of carbohydrates, proteins and fats by enzymes secreted from the pancreas and small intestine. Bile is also secreted from the gallbladder for emulsification of the fat particles in our food so that the lipases can perform their job properly. The pancreatic juice is alkaline; the enzymes in the small intestine work best in an alkaline environment (i.e., with high pH). The control of the secretions from the gallbladder, pancreas and small intestine is both hormonal and neurological. The enzymes for each class of food (carbohydrates, proteins and fats) are specific but they make no distinction whether the food comes from animal or vegetable sources. The chief goal of the whole digestive process of food is to break down the three main components of food into their end products of simple sugars, (glucose, fructose and galactose), amino acids, fatty acids and glycerides. The mechanisms of the absorption and utilization of these end products are too complicated for further discussion in this article.


The orthodox school believes that our body is able to manufacture sufficient enzymes to metabolize our ingested food. Exogenous food enzymes would be required when there is a deficiency of such enzymes in our body. In cases of malabsorption due to pancreatic insufficiency, physicians prescribe pancreatic digestive enzymes (eg. pancreatin) as a replacement therapy.

However, over the past half century, a new concept of food enzymes has been proposed by some well known scientists, one of whom is Dr. Edward Howell. His good work is well presented in his two famous books:

  1. Food Enzymes for Health and Longevity, Omangod Press (1980)
  2. Enzyme Nutrition, Avery Publishing Group Inc. (1985)

Dr. Edward Howell, who is also known as The Father of Food Enzyme Research by nutritionists, has his own concept of food enzymes and their use. For the sake of simplicity, the whole concept can be summed up as follows:

  1. Each one of us is given a limited supply of digestive enzymes at birth. This supply has to last a lifetime. The faster you use up your enzyme supply, the shorter your life will be.
  2. Raw food contains good amounts of food enzymes which are easily destroyed by modern cooking. We obtain no exogenous food enzymes from our well-cooked food.
  3. Exogenous enzymes from raw food are activated when the cell wall of the food is ruptured by chewing, and continue to function not only in the stomach but also in the upper part of the small intestine. Their activities work in a wide range of pH as compared with the endogenous digestive enzymes.
  4. The Law of Adaptive Secretion of Digestive Enzymes. In 1904, The Theory of The Parallel Secretion of Enzymes was published by Professor B.P. Babkin in Russia. It stated that the three main digestive enzymes (amylase, protease and lipase) were secreted at the same strength, regardless of whether the food eaten was carbohydrate, protein or fat. This theory was accepted by many scientists, but not all. Another theory was proposed as early as 1907 and stressed again in1930. It held that only the corresponding enzymes of that particular food would be adequately secreted in the digestive system. Thus, one would expect that a baked potato would stimulate only the secretion of amylase (a carbohydrate digestive enzyme). Similarly, a piece of lean meat, containing mainly protein substance with little fat and carbohydrate, would cause the secretion of protease enzymes with token amounts of lipase and amylase. This selective secretion of digestive enzymes was said to be present in man as well as in animals. Dr. E. Howell called this The Law of Adaptive Secretion of Digestive Enzymes.
  5. The Enzyme Bank Account. According to Dr. Howell, we are born with a limited supply of enzymes at birth. To put it in banker's language, each of us has a fixed amount of capital (enzymes). Our balance in the bank will depend on the number of deposits and withdrawls. We credit our account by continuously ingesting raw food and food enzyme supplements. We debit our account by draining away our precious enzymes when we routinely consume cooked or processed foods. If the withdrawls are greater than the deposits, we eventually come to a negative balance. Dr. Howell stated clearly in his book called Food Enzymes for Health and Longevity, " When we eat cooked, enzyme-free food, the body is forced to produce enzymes needed for digestion. This depletes the body's limited enzyme capacity. This 'stealing' of enzymes from other parts of the body sets up a competition for enzymes among the various organ systems and tissues of the human body. The resulting metabolic dislocations may be the direct cause of ... many chronic incurable disease (5)."
  6. The vital force. Dr. Howell and other scientists challenged the idea that enzymes are only lifeless catalysts with certain chemical structures and reactions. They consider enzymes to possess a vital force or "biotic energy". In this publication, "The Status of Food Enzymes in Digestive and Metabolism", Dr. Howell wrote: "It is no longer warranted to consider vitality and life energy as intangible forces. The available evidence does not justify a placid continuance of nihilistic attitude toward the vital forces operating in the living organism. Enzymes emerge as the true yardstick of vitality. Enzymes offer an important means of calculating the vital energy of an organism. That which has been referred to as vitality, vital force ... probably is synonymous with that which has been known as enzyme activity..."

Dr. Howell was not alone in holding this concept which is equally shared by prominent scholars like Professor Moore of the University of Oxford in England, professor Willstatter of Munich in Germany and Northrop of Rockefellar Institute for Medical Research.


Digestive enzymes are widely used by practicing orthodox physicians as well as by nutritionists who are faithful students of Dr. Howell's School of Food Enzymes. Physicians prescribe digestive enzymes and bile preparations because they want to correct deficiency states in their patients. This is a form of replacement therapy. The nutritionists advocate the liberal use of food enzymes in normal persons to achieve optimal health and longevity. With the introduction of a number of food enzymes, they hope to enhance digestion. By the addition of some herbs they aim at healthier supplementation, more efficient detoxication, and greater stamina. However, Dr. Howell strongly advises lay people who would like to try The Food Enzyme Therapy, to seek advice from a qualified Health Professional.

Ordinary digestive enzymes sold over the counter (OTC) are prepared from either animal or vegetable sources. For example, Pancreatin B.P. comes from the animal source and will not be accepted by vegetarians. Unripe papaya and pineapple will yield digestive enzymes for proteins only. The vegetarians should not be disappointed because scientists have found a good source of digestive enzymes in the Asperigillus plants. These enzymes work on the full range of fats, proteins, carbohydrates and cellulose. When the strict vegetarians use these products, they must not forget to discard the capsules which are of course derived from animal sources. Either empty the capsules into food before eating them or mix into room temperature beverages. 


Digestive enzymes are significant because digestion of food is impossible without them. In a young and healthy person, there may be an adequate supply of digestive enzymes to handle the whole process of digestion. Conventional wisdom uses digestive enzymes as a replacement supplement. It also advocates the ingestion of raw fruits and vegetables which have a high content of vitamins and food enzymes. Dr. Howell's use of Food Enzymes suggests that the supply of human enzymes is limited at birth. The faster we consume our enzymes, the shorter will be our life span. Raw food is a good source of food enzymes. Ingestion of raw food or enzyme supplements will lessen the work of our digestive system so that more energy is reserved for other metabolic activities. This new concept in the use of food enzymes has already created a third wave in the Nutritional Supplement Industry following in the footsteps of vitamins and minerals. When I was preparing this paper, I had a dream, there was a simple but conscientious mother who had two good sons with different beliefs. One chose to balance a life of hard work living in a relatively polluted environment with adequate diet and exercise. The other son chose a life similar to the primitive Eskimo with a lot of raw food, fresh air and peace in the Arctic. While the anxious mother was contemplating the pros and cons of the different lifestyles of her two beloved sons, my alarm clock woke me up from my dream before she could decide which son was right. What a misfortune! I therefore got up and dressed myself to prepare for my daily work - the quest for excellence.


I would like to thank Mr. Barrie Carlsen for advice and criticism, and Ms. Julie-Ann Warren, the Executive Secretary, for preparing my manuscript.


  1. Chiles, V., Canadian Self-Medication. First Edition, Canadian Pharmaceutical Association 1980.
  2. Howell, E., Food Enzymes for Health and Longevity, Omangod Press. Page xiii, 1980
  3. Skadhange, E., (Editor, Intestinal Absorption and Secretion, MTP Press Limited, 1984
  4. Howell, E., Enzyme Nutrition, Avery Publishing Group Inc., 1985
  5. Kromhout, D. et al, The Inverse Relation Between Fish Consumption and 20-Year Mortality From Coronary Heart Disease, New Engl. J. of Med. Vol, 312: 1205-1209, 1985