Why do people supplement enzymes to perfectly healthy dogs?

This is a very common recommendation, especially among raw feeders, that I have failed in understanding. Let's back up a minute.

Enzymes are vital to growth and life. Digestive enzymes break down fats, proteins and carbohydrates so that food is transformed into building blocks that can be absorbed by the intestine. Metabolic enzymes are present in every cell to allow the cell to do its work, which is usually producing a functional product of some sort, or maintaining its structure for support of body activities.

Supplementation of metabolic enzymes is not common, and even if it were, not much make it to the cells that the supplementer is theoretically targeting because they would be, to a large degree, digested in the GI tract and not absorbed in whole, functional form. On the other hand, digestive enzymes are active right in the gut where we put them. We use them for animals who have diminished digestive capacity, such as those with exocrine pancreatic deficiency, or in geriatric animals who may have atrophy in some of the cells that produce these enzymes.

Sounds good on the surface of it - help animals digest their food better. But that implies that there is some problem with digestion in healthy animals. Here's the rub - supplementation of pancreatic enzymes actually *inhibits* normal pancreatic enzyme excretion. In fact, we use digestive enzyme supplements in dogs and people with pancreatitis for just this purpose - to suppress the release of pancreatic enzymes which contribute to the pain of pancreatitis after meals.

So not only are paying for expensive enzyme supplements that probably are not necessary, but we are chronically telling a normal pancreas not to do its job.

Here is just a recent clinical study that proves this feedback inhibition in people, and it has been shown in dogs as well.

Walkowiak J, Witmanowski H, Strzykala K, Bychowiec B, Songin T, Borski K, Herzig KH. Inhibition of endogenous pancreatic enzyme secretion by oral pancreatic enzyme treatment. Eur J Clin Invest 2003; 33 (1): 65–69

Nustede R, Schmidt WE, Jager M, Stockmann F, Kohler H, Folsch UR et al. Gastrin-releasing peptide and CCK after intraduodenal inhibition of proteases in dogs. Int J Pancreatol 1994;15:209–14.

So I'd like to hear convincing arguments from those who recommend supplementing healthy animals with digestive enzymes. Why do it and what proof do you have that it's good for them?