COMMENT: Howell reiterates these points several times, but once again never presents credible proof for his claims. Digestive enzymes are made in the parotid glands, submandibular glands, sublingual glands (saliva), stomach, pancreas, and in the small intestine mucosa and submucosal glands. One wonders how the pancreas (as Howell alleges) can somehow magically prevent the manufacture of metabolic enzymes in the blood, lymph system, or brain of a person. Can the pancreas somehow "vacuum up" all the precursors?

Apparently this is supposed to happen by a process whereby the pancreas creates a drain on "precursors" from some common pool--but one which is never located or biologically delineated, and conveniently left vague and purely speculative. An analogy that has been put forth by one raw-foodist supporter of Howell today likens the body to an electronic computer's multitasking CPU which has to split its available processing cycles or energy supply between various "tasks," which are then equated with enzymatic manufacturing processes (or vaguely, "energy use") in the body. But again, the analogy is left conveniently imprecise without delineating the corresponding biological pathways or counterparts that might actually behave this way.

Confusion over "recycling" of enzymes has contributed to flawed claims. The idea that your body must "rob" materials from metabolic enzyme production in order to produce digestive enzymes is at the heart of Howell's theories. If the claim were true, one would expect the body to be efficient at recycling enzymes, particularly in intact forms. Indeed, one claim occasionally made by today's promoters of Howell's theories is that digestive enzymes are recycled intact in just such a fashion.

It is likely that part of the reasoning behind this idea that enzymes can get recycled between very different bodily systems arises out of confusion over just what the well-known "recycling" properties of enzymes actually refer to. As mentioned earlier, enzymes do in fact get "recycled" on a limited basis--though to put it more precisely, what actually happens is that they are immediately reused (multiple times in quick succession) during their specific phase of intended "use"--i.e., say, for the limited period of time in the stomach or intestines during which they are breaking down a specific food substrate.

This well-known, localized, phase-specific recycling is much different, however, than the type of body- or system-wide recycling being proposed by proponents of Howell. More accurately, then, to better distinguish the latter type of "recycling" from the former, what Howell's promoters are proposing here would be better termed a process of "shuttling" enzymes between different enzyme production systems in different parts of the body. Let's examine these claims and find out what they tell us about Howell's theories.

Enteropancreatic circulation of enzymes? In the late 1970s and early 1980s, a few scientific papers were published claiming that there is an enteropancreatic circulation of digestive enzymes. By the term "enteropancreatic circulation," these papers proposed that excess pancreatic enzymes are absorbed from the intestines into the bloodstream; the enzymes are then circulated through the bloodstream, and resecreted by the pancreas--i.e., they are shuttled around and eventually recycled as a conservation measure.

Although this is not identical to the claims of Howell himself, there is some commonality, as this theory suggests that human physiology actively seeks to preserve enzymes, i.e., in Howell's terminology, to preserve the "enzyme potential." Further, being realistic about it, the idea of "enteropancreatic circulation" would probably have to be considered the best modern translation of the form that Howell's dated hypothesis of an "enzyme potential" would need to assume in order to be taken seriously. And it is probably a fair approximation of how the assertions made by his supporter's today would have to be rendered in biological form, if they are also serious about translating the idea that enzymes get shuttled/recycled into a meaningful form amenable to real scientific evaluation.

Early studies claimed existence of enteropancreatic circulation of enzymes. The papers of Liebow and Rothman [1975], Gotze and Rothman [1975], Heinrich et al. [1979], among others, claim to prove the existence of such an enteropancreatic circulation. The efficiency of the circulation in these studies was controversial; Gotze and Rothman claimed 60-90% efficiency, while Heinrich et al. reported only 1%. Occasionally, some of these studies are cited by raw diet advocates in support of the general theories of Howell, and allegedly as evidence that one needs to eat primarily raw/so-called "enzymatic" foods.

More modern radioactive-tracer studies demonstrate little or no evidence of enteropancreatic circulation. A number of subsequent studies made since then, however (which usually are not cited by raw diet advocates), have found no, or very limited, evidence of enteropancreatic circulation of enzymes.

• Studies with dogs. Bohe et al. [1984] injected radioactive-labeled trypsin into dogs, and found that only 0.15% of the radioactivity was secreted into the dog's pancreatic juices. Levitt et al. [1981] injected radioactive-labeled amylase into dogs, and found that less than 0.02% of the radioactivity was excreted in pancreatic juices. The result of both of these studies clearly demonstrates via radioactive tracers that enteropancreatic circulation in dogs is very limited, and such circulation is not biologically significant.

• Studies with rats. Rohr et al. [1981], using radioactive tracers, proved that there is no enteropancreatic circulation of any kind in the rat. In two other studies, Urban et al. [1982] and Urban and Zingery [1982] analyzed rat intestines and found them relatively impermeable to ribonuclease, a major element of pancreatic fluid. This research adds further support (though in itself is not a direct proof) that there is little or no enteropancreatic circulation in the rat.

  A major study that clearly discredited the theory of enteropancreatic circulation was that of Rohr and Scheele [1983], who injected radioactive pancreatic proteins into the bloodstream of rats and studied the absorption. They note [Rohr and Scheele 1983, p. 991] (emphasis below mine):

  The majority of pancreatic proteins (~97%) were taken up by a variety of body tissues, particularly kidney, liver, spleen and lung...

  These studies indicate that pancreatic proteins are removed from the blood circulation by at least three separate pathways: (a) uptake and degradation by a variety of tissues in the body (~97% of injected radioactivity), (b) excretion of intact proteins into urine (1%-2%), and (c) transport of intact proteins into bile (0.3%-0.5%). Transport of exocrine pancreatic proteins from the blood circulation to pancreatic juice could not be demonstrated.

• Initial studies "proving" enteropancreatic circulation were flawed and invalid. Scheele and Rohr [1984] and Rohr et al. [1981] provide a detailed critique of the errors in the earlier studies that found an enteropancreatic circulation of enzymes, and explain why the studies are invalid. In particular, Rohr et al. [1981] report that the results of some of the previous studies actually reflect the metabolic breakdown of the radioactive enzyme, followed by reuse of the radioactive tracer protein by the pancreas to make new enzymes (i.e., the earlier studies were misinterpreting their data and/or lacked controls to make sure the enzymes measured were actually exogenous). Scheele and Rohr [1984] also mention the possibility for input of exocrine pancreatic proteins via diffusion; however, such an input process will necessarily support only very low levels of enzyme output.

For the sake of discussion, however, let's now assume (pretend) that some digestive enzymes are assimilated, broken down via the protein cycle, and the base proteins are then used by the pancreas to make new enzymes. Interpreting the results of Heinrich et al. [1979] as reflecting such a stepwise metabolic processing of enzyme proteins suggests that the recycling of pancreatic (digestive) enzyme protein results in a reuse of at most 1% of the digestive enzyme proteins. (The study of Gotze and Rothman [1975] is unreliable and invalid, hence their higher reuse figures will not be analyzed here; see Scheele and Rohr [1984] for a critique.)

Enzymatic precursors: scarce or abundant? Now let's link this to Howell's theories. The extremely low levels of enzyme protein recycling/reuse noted in the preceding paragraph indicate, to use Howell's terminology, that the "enzyme precursors" are not scarce but instead are present in great abundance. This, of course, directly contradicts Howell's claim that one must "rob" from metabolic enzymes in order to make digestive enzymes.

COMMENT: No one with an interest in dietary issues doubts that a natural diet approximating an animal's wild diet is superior to feeding them a human diet (cooked or not), and for many reasons unrelated to enzymes.

COMMENT: Cooking affects a food in numerous ways, not only by destroying enzymes. In particular, heating produces Maillard molecules which reduce lysine availability (see above). We also have seen that reduction of digestibility can be caused by many other factors than enzyme destruction.

COMMENT: The claim that the traditional Inuit diet was a raw-food diet is simply a legend, not fact, and has no proof to back it up. In fact, early contact reports with the Inuit, reviewed in the section, The traditional diet of the Inuit: Were they the only raw-food culture? indicate that the traditional Inuit diet was a mixed diet, cooked plus raw. (Sufficient data are not available to determine whether the traditional Inuit diet was a mostly raw-food diet according to the definition used here, i.e., 75+% raw by weight.) Thus Howell's claim that the Inuit were rawists is dubious at best.

However, for the sake of discussion, let us assume that the Inuit diet (at least in some cases) was a raw-food diet in the modern sense. We observe that the claim suffers from the same logical fallacy as the previous two claims: If A is proposed as being caused by B, but can also be, or is already known to be, caused by C, D, E, and F, etc. (which the enzyme proponent completely ignores), one cannot simply pin blame on B (cooking in this instance) by fiat, merely by arbitrarily choosing to completely ignore the many other factors.

Modern Inuit eat Westernized diets with all that that entails, not simply, or only, "cooked" foods. We won't expand much further here, but it is clear that those Inuit (if any) who followed a predominantly raw diet, who then became Westernized, not only started to eat more cooked foods, but their diets became increasingly Westernized as well (e.g., highly processed foods, refined sugar, etc.). Much modern research has demonstrated that Western diets are harmful due to numerous factors that have little or nothing to do with cooking by itself. For example, cardiovascular disease was almost nonexistent in those following a traditional Inuit lifestyle [Schaeffer 1981]. Possible causal factors include their low-carbohydrate diet (hence low insulin secretion) and a favorable fat profile (polyunsaturated fatty acids from fish). Other evidence indicates that cancer was very rare among the Inuit living their traditional lifestyle; Stefansson [1960], Schaeffer [1981].

Finally, we note that if one does not assume that the traditional Inuit diet was a raw-food diet in the modern sense, then Howell's claims about enzymes in the "raw" Inuit diet become irrelevant.

COMMENT: Here, Howell fails to mention clearly that the main point of the experiment by McKay et al. was to study the effect of calorie restriction on longevity. Many rats showed diverse signs of pathology at old age, but obviously some physical degeneration is predictable.

A glance at the article shows that the rats were fed a diet of (numbers in parentheses indicate percentage contribution to the diet by weight): casein (40%), starch (22%), sucrose (10%), lard (10%), dried yeast (5%), cod liver oil (5%), salt mixture (6%), and cellulose (2%). At the time, the authors considered the diet vitamin-adequate, and didn't supplement it with any vitamin mixture, but it is important to note that, at that time, all the vitamins and essential fatty acids hadn't been discovered yet, and that the nutritional requirements of rats weren't well-determined. Here again we can see the problems involved when raw-food theory grasps at such badly out-of-date research to rely on for support. To get an idea of the state of nutritional knowledge in the 1930s, folate was discovered in 1941 and synthesized in 1948; vitamin B-12 was isolated in 1948.

The diet of these rats was deficient and much less elaborate than what laboratory animals receive nowadays; compare for instance with Weindruch [1986], where rats get complete vitamin and mineral mixtures, in addition to casein, cornstarch, sucrose, corn oil, mineral mixture, fiber, brewer's yeast, and zinc oxide.

It is true that laboratory rats show signs of disease at old age in contemporary experiments, but at least part of the diseases can be explained by the natural degenerative process: no diet can maintain anyone young forever. In addition, a fair amount of the protein is from casein, which can hardly be considered as part of their natural diet, and which actually can cause kidney pathology [Iwasaki et al. 1988], as well as be a source of antigenic dead microorganisms [Wostmann et al. 1971]. (Something is said to be "antigenic" if it triggers the formation of antibodies by the immune system. The purpose of antibodies is to get rid of antigens, which are perceived by the body as "foreign" or detrimental.)

COMMENT: The fact that enzymes taken as tablets with protective coatings (to avoid destruction by stomach acid before they reach the small intestine) might be of therapeutic value for some individuals (particularly those with inherent or genetic problems with enzyme metabolism) doesn't mean they are helpful for everyone else or for human health in general. Nor does it mean that the food enzymes that accompany raw foodstuffs have an equivalent effect.

One cannot compare the large amounts we get with enzyme therapy (i.e., enzymes taken in capsule or tablet form) with the enzymes in food itself. Most enzymes in food are destroyed by the stomach acids. In formal enzyme therapy, the tablets or capsules that people swallow are soluble only in the small intestine (so that the enzymes are not destroyed by the stomach acids), taken outside meals (to improve absorption), and probably in larger quantities and concentrations than what occurs naturally, since foods contain a mixture of many different enzymes, which appear at more modest concentration.

Such enzyme therapy via tablets or capsules with protective coatings is no doubt useful for individuals whose bodies lack the capacity to produce certain enzymes at all. Again, however, the (very) small amount of enzymes in food itself that might be able to make it through the stomach into the intestine will not have much significant therapeutic effect for these individuals.

Some readers will note there are anecdotal claims that oral enzyme therapy using uncoated tablets (usually chewable) and/or uncoated capsules, is effective for some. Such tablets typically contain relatively large amounts of enzymes when compared to the amounts in food, and may have a limited effect--if the dose is high enough--before the digestive acids destroy the enzymes in the stomach. However, the possibility that extremely large doses of digestive enzymes, in chemically isolated and purified form, might have an effect when taken with food is really not a substantive argument for eating a 100% raw-food diet, as the amount of enzymes contained in raw foods is small in comparison to the supplements. Further, some enzyme supplements also contain mint oils--and mint has a long history of use in traditional/folk medicine as a stomach-soothing herb. That is, in some cases, the effect observed from enzyme supplements may actually be due to the peppermint (or other mint) content of the supplement.

What about the "enzyme synergy theory"?

...[E]nzymes that occur naturally with those in foodstuffs can act synergistically with those in the human digestive tract to release the maximum amount of thermodynamic free energy from the food...

Energy is defined in this report as the thermodynamic free energy of the chemical bonds in the foodstuffs...

The resulting metabolism of the smallest components (amino acids) results in the release of thermodynamic free energy which drives cellular functioning.

• The very fickle nature of hydrogen bonding in water (note that many raw foods are high in water).
  
• The huge variety of chemical reactions involved in digestion, many of which are multi-stage reactions.
  
• We really don't know all the reactions that occur in digestion.

Logical fallacy in analogizing from survival of stomach acid by enzyme-inhibitor proteins to other proteins such as food enzymes. The (nominally) strongest support for Prochaska and Piekutowski's theory is provided by the enzyme inhibitors in raw legumes and grains, but the accompanying reasoning is problematic at best. That is, the point is made that such inhibitors are proteins and survive stomach acid, hence other proteins (enzymes) can and will survive the stomach acid as well. Insofar as digestion is a slow and imperfect system, some small amounts of enzymes apparently do survive. However, enzyme inhibitors have a different structure, and the fact that some inhibitors survive stomach acid does not lead to the conclusion that food enzymes are even remotely as robust.

In apparently suggesting that raw legumes be consumed, Prochaska and Piekutowski also seem to ignore the important reality that raw soaked (or sprouted) legumes, except for a very few (mung, lentil adzuki, green peas, maybe chickpeas) have such an unpleasant flavor that one cannot eat them. In contrast, cooking makes it possible to eat a wide variety of legumes. That the enzyme synergy theory suggests one eat raw legumes is of little import when one tastes certain raw legumes and finds them inedible.

The authors narrowly focus on negative effects of cooking, while ignoring the positive ones in favor of net energy gain. Vitamin loss, protein degradation caused by excessive cooking, and even the formation of resistant starch are mentioned in this regard. At the same time, Kataria and Chauhan [1988] is present in their listing of reference sources, but they fail to mention that the same study authors [Kataria and Chauhan 1988, p. 57] say that "starch digestibility increased more than six-fold as a result of ordinary cooking of soaked mung beans"; and that mung beans soaked 12 hours have a starch digestibility (mg maltose released per gram) of 25.3, while soaked seeds pressure-cooked for 5 minutes have a starch digestibility of 305--over 10 times that of uncooked ones (Tables 1, 2, pp. 54-55 of Kataria and Chauhan [1988]).

This increase in starch digestibility is very important in real energy terms (calories), as starch is the predominant energy source for most people on this planet (i.e., most veg*n diets and the diets of lesser developed countries, are starch-based). It is hard to see just how energy as defined in Prochaska and Piekutowski has any real significance and connects to calories.

Sotelo et al. [1987] is cited in Prochaska and Piekutowski as evidence that cooking does little to enhance the digestibility of chickpea protein. However, more recent research [Clemente et al. 1998, abstract] indicates that "appropriate heat treatment may improve the bioavailability of chickpea proteins."

Additional muddled logic. Prochaska and Piekutowski discuss research in which chickens were fed oral enzymes which increased the digestibility of certain grains; they conclude that it provides evidence enzymes can survive the digestive tract. However, that is not necessarily the case--a more plausible explanation is that the enzymes acted in the stomach before being neutralized by stomach acid, i.e., the enzymes didn't necessarily survive the stomach.

Other doubts. Finally, the theory is based on unpublished writings by Piekutowski. The title of one of these papers: Cancer--Disease of Energy Deficiency--raises doubts as to whether it is a credible scientific paper, or may instead be the kind of food-faddist writings common in the raw diet community.

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