A digestive enzyme is a substance naturally secreted by the body which supports and accelerates - ’catalyses’ - the chemical reactions governing digestion. Its main function is to break down the large molecules (polymers) that make up food into smaller ones (monomers) so that absorbable nutrients can be released at the site of the intestinal villi (1).
Digestive enzymes are produced by various organs and glands throughout the gastrointestinal tract. They are primarily secreted in the mouth, stomach and smallintestine (2). In medical terminology, they are identified by their -ase suffix (or less commonly, -ine).
Importantly, each digestive enzyme has a unique binding site which allows only one type of substrate to be identified, accepted and broken down, like a key in a lock. This albeit-simplified analogy illustrates the specific and selective character of enzymatic activity (3). A protease, for example, can only break down proteins.
As a reminder, proteins are made up of polypeptide chains, which are themselves comprised of amino acid building blocks. The role of proteases (or proteolytic enzymes) is to split all the polypeptide bonds in order to extract the amino acids, the only parts able to cross the intestinal barrier .... (4).
Protein digestion begins in the stomach with the activation of inactivated enzymes called pepsinogens into pepsin under the effects of hydrochloric acid (5). This active enzyme splits the proteins into polypeptides.
This is followed by the secretion in pancreatic juice of two inactive proenzymes, trypsinogen and chymotrypsinogen. Once in the duodenum (the first part of the small intestine), these are converted by enterokinase into their active forms, trypsin and chymotrypsin.
It is these enzymes, part of the peptidase family, which go on to break the polypeptides into chains of three (tripeptides) or two (dipeptides) amino acids (6-7). Their work continues at the surface of enterocytes, where the amino acids are finally isolated.
As their name suggests, lipases (lipolytic enzymes) act by breaking down lipids into fatty acids (8).
When they arrive in the duodenum, fats are first emulsified with bile salts from vesicles. This first stage facilitates the task of the major lipid breakdown enzyme, pancreatic lipase (9). Produced by the pancreas, this converts lipids into fatty acids and glycerol. As with proteins, this conversion concludes at the enterocytes.
These fatty acids then enter the lymphatic system packaged into chylomicrons, before later arriving in the bloodstream (10).
Carbohydrate digestion involves a wide variety of enzymes as they have to be able to adapt to the diversity and complexity of the sugars we consume. Their ultimate goal is to reduce these down to three simple sugars (-oses) that can be absorbed by the body: glucose, fructose and galactose (11).
For complex sugars (polysaccharides) such as the starch in carbohydrates, the first step takes place ... in the mouth! Saliva contains amylase, an enzyme which triggers the cleaving of polysaccharides into maltose and dextrins (12). Operating at a slightly acid pH (around 6.8), salivary amylase stops acting once it reaches the stomach where it is broken down by gastric juices.
This breaking down of carbohydrates continues courtesy of the pancreas and pancreatic amylase. Its function is twofold: to process polysaccharides that may have escaped the salivary amylase, and to cleave the dextrins into the disaccharides (double sugars) maltose and isomaltose (13).
Disaccharides, whether from food or the breakdown of polysaccharides, are finally separated into -oses, as a result of specific enzymes expressed on the surface of enterocytes:
In certain circumstances, there may be a decline in the body’s digestive enzyme production. In addition to diseases affecting the gastrointestinal tract, factors related to age, heredity or gut flora imbalances may play a part (18-19).
This primarily manifests in digestive discomfort and even weight loss due to inadequate nutrient absorption. In such cases, it makes sense to give the body a helping hand by supplementing with digestive enzymes (20).
As well as the essential proteases, lipases and amylases, cutting-edge enzyme supplements also contain enzymes not produced by the body which are used in processing sensitive foods. One such enzyme is cellulase responsible for breaking down cellulose (the main fibre in plants) (21).
In addition, the effects of digestive enzymes can be maximised by combining them with certain phytonutrients that benefit digestive health. These include green aniseed for reducing flatulence and bloating (22), peppermint for its antispasmodic and carminative effects (23), and fenugreek which plays a role in carbohydrate and lipid metabolism (24). The synergistic supplement Digestive Enzymes combines, in a single capsule, 15 important digestive enzymes, including lactase, several proteases and cellulase, as well as all the plant extracts mentioned above.
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