If you've ever perused the supplement shelves at your health food store or drugstore, you may have noticed a variety of enzyme supplements available for purchase. Some of these refer to themselves as "systemic enzymes," meaning that they are meant to function in the body as opposed to in the digestive tract. By contrast, proteolytic enzymes are generally meant to augment digestion.
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Proteolytic enzymes digest protein, meaning that they break it down into its constituent molecular building blocks, which are called amino acids. Your digestive tract relies upon many different proteolytic enzymes to help you digest your food, explains Dr. Lauralee Sherwood in her book "Human Physiology." There are also proteolytic enzymes that occur in certain foods -- papaya, for instance, contains the proteolytic enzyme papain. For this reason, papaya is a popular meat tenderizer.
While you may see the term "systemic enzymes" on supplement bottles, it's not a useful biochemical term, nor is it used in medicine or science. In general, however, when manufacturers refer to an enzyme as "systemic," they mean to suggest that it will participate in reactions within the body cells, outside the digestive tract. Some systemic enzymes, for instance, are advertised to help you lose weight, treat symptoms of diabetes or improve organ function.
The problem with enzyme supplements in general -- proteolytic and otherwise -- is that there's really no evidence that most enzymes from non-human sources have activity in humans. Part of the problem is that enzymes are very sensitive to acid; if they're not meant to operate in an acidic environment, acid destroys them, explain Drs. Mary Campbell and Shawn Farrell in their book "Biochemistry." As such, most of the proteolytic and systemic supplements available at stores are simply digested by your stomach acid and have no activity in the body.
While there is some evidence to support taking certain digestive enzymes -- lactase, for instance -- to aid in food digestion, there's no evidence whatsoever that you can move an enzyme from the digestive tract into the cells. For this reason, it's not likely that so-called systemic enzymes can ever leave the digestive tract and engage in the reactions in which they're advertised to engage. Further, true enzyme deficiencies in humans are quite rare -- and aren't treated by supplementing with enzymes.