A Primer on Enzymes

July 10, 2007
For those who can't digest lactose, lactase can make short work of the problem. Lactase is an enzyme that splits lactose into its constituent sugars, glucose and galactose.

That's how products like Lactaid allow lactose-intolerant individuals to indulge their dairy fantasies. Or maybe beans stir-up digestive trouble, forcing you to pass...well, let's just say pass up a great source of soluble fiber. Here's where products like Beano come to the rescue, supplying starch-digesting enzymes.

When digestive enzymes are in short supply, enzymes from food or supplements can aid digestion, providing the needed molecule-splitting power. But enzymes cannot pass the barrier of the digestive system to enter the bloodstream and function as enzymes and herein lies the problem with treating enzymes as nutrients or as dietary essentials. The burden of proof lies with the advocates of this position to show that enzymes enter the blood and act as enzymes. That's no easy task -- in fact it appears to defy common sense.

Enzymes are a class of very large protein molecules and are needed to control virtually every reaction in the body. They do so by lowering the energy necessary for a reaction to happen -- the so-called energy of activation. The body -- or any living organism -- has only a narrow range of temperature and pH to work within, so altering the conditions that allow vital reactions to occur is essential to life. "Burning fuel" to produce free energy and ultimately movement is something both your car and your muscles do for a living. But the conditions are very different.

Enzymes lower the energy of activation in a very specific manner: They bring the reacting molecules together so that they are positioned just right, forming a complex with the enzyme (often described as a lock and key arrangement).

This positioning step is what saves so much energy, allowing all manner of oxidations, reductions, synthesis and degradation of material to happen at a temperature and pH range that is compatible to life. The specific nature of these reactions is why we make our own enzymes -- thousands of them -- according to the instructions we call genes.

Enzymes aren't vitamins, which are, by definition, made outside of our body and considered dietary essentials. For example, vitamin D, essentially a hormone, is made in the skin upon stimulation by UV radiation. Some enzymes are secreted into the digestive system in response to food, where they perform the specific functions of breaking apart the molecules of proteins, fats, starches, and sugars, depending on the specific enzyme.

If you add an outside source of enzymes, they may aid this process, but that is a far cry from enzymes acting as nutrients. Nutrients pass through some pretty powerful barriers designed to protect the body from foreign invasion. After all, the digestive system is basically a 26-foot, open-ended tube.

Any protein -- even an enzyme -- entering the digestive tract must first deal with the hydrochloric acid of the stomach, which is there to denature (unfold) the protein. This allows proteases (protein-digesting enzymes) to break apart the protein into its constituent amino acids. It's the amino acids that get absorbed in the small intestines, not the intact protein.

The protein-digesting process even destroys the starch-digesting enzymes that naturally occur in saliva. Starch digestion is mostly carried out in the small intestines by pancreatic enzymes.

Even if an intact protein somehow managed to escape the digestive process to enter the blood, it would be treated by the immune system as an invading organism and attacked. This is precisely what a healthy immune system does: It attacks and destroys foreign proteins.

But the enzymes-as-nutrients contingent insists on dragging out obscure arguments to make the case that enzymes are a dietary necessity, implying -- not proving -- that enzymes from plants or animals enter the blood via diet to perform vital tasks.

The enzymes-as-nutrients argument uses a chain of known facts in a "connect-the-dot" approach to science that logically does not connect:

  • Dot one -- enzymes are vital to life. (This is true, but of the enzymes our bodies make within. It's not a revelation that argues for their dietary importance.)
  • Dot two -- enzymes diminish with age. (So does everything else; that's why our body is constantly turning over the enzymes it makes.)
  • Dot three -- it requires energy to make enzymes. (So does every synthetic reaction, and muscle contraction, and thought process. Again, this is an argument for eating healthy, not for taking enzymes.)
  • Dot four -- intact proteins enter the blood through the gut of infants. (Maternal antibodies pass through the placenta to the fetus using a special receptor on the placental cell. Also IgA antibodies found in breast milk are transferred to the infant's gut as protection against bacterial infections, until the newborn can synthesize his or her own antibodies. These specialized instances are used to "prove" that intact proteins from diet escape digestion at will in adults eating raw food. That doesn't happen.)
  • Dot five -- enzymes are abundant in raw food. (Many nutrients are abundant in raw food. The body breaks those down during digestion, too.)
  • Dot six -- cooking destroys enzymes. (Cooking destroys many nutrients, but it also makes some nutrients more available.)
  • Dot seven -- cooking is "unnatural" because enzymes are destroyed. (This often shows up as the endpoint of the argument for treating enzymes as dietary essentials. Somehow we humans "fell from grace" by learning to cook food   the downfall of our health, our expulsion from the garden of eatin' healthy, etc. But it ignores one important fact: Cooking and otherwise processing foods makes certain nutrients available that would otherwise be difficult to attain. The "raw foodists" who insist we eat like our ancestors never insist we shoot for the same lifespan of about 30 years that our ancestors enjoyed.)

We can't ignore the fact that heat and acid destroy enzymes. As aids to digestion for people who have difficulty with beans or have insufficient digestive enzymes -- the old, the infirm --they could be of value in the stomach. As supplements or nutraceutical ingredients, especially for healthy persons, they cannot function once they've been broken down in the stomach. They simply become a very expensive form of protein.

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