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The wise, health-promoting nutritional advice offered by the vegetarian
doctors who defined naturopathy as well as the recent research detailing
the benefits of vegan/vegetarian diet on our kind done by Pritikin
& Ornish (heart), Wahlqvist and Aldercreutz (menopause), Lindahl
(asthma), Barsotti (kidney disease), the Farm Collective (uncomplicated
home births) and Chen, Peto et al (general health, cancer) is being
ignored by naturopathic physicians who subscribe to the blood type
diet theory.
We feel this is a mistake.
The foundation for the blood type diet theory is comprised of three
"legs" as the author himself points out. As we read them
the individual legs contain inaccuracies which render each one scientifically
and logically flawed. The diet theory they support is, then, rendered
invalid.
"Leg One" is the lectin hypothesis. The foods we eat
contain lectins. Because of how lectins clump (or "agglutinate")
other molecules they have the capacity to create health problems
for human beings. Botulism toxin has a lectin, ricin, that is so
deadly you would never encourage someone to consume it. On page
27 of the book explaining the blood type diet, it is stated that
certain lectins "agglutinate cells in the affected blood type"
as "visible under the microscope". The author assumes
that this same clumping seen in office on a slide beneath a microscope
occurs in the bodies of people of particular blood type, making
them unwell if they don't choose their foods as recommended by the
blood type diet theory. Extrapolating from results observed in a
test done on a laboratory slide to effects in a human being has
several disadvantages. Observed in vitro morphological changes in
blood are controversial regarding their "validity and reproducibility"
as well as "the most common criticism" that "the
technique is susceptible to the subjective judgments of technicians
and that the methods used by different labs produce widely varying
results" (Stephen Barrie, N.D. in A Textbook of Natural Medicine
by Joseph Pizzorno, N.D. and Michael Murray, N.D., John Bastyr College
Publications, Seattle 1987, Sect II Supplemental Diagnostic Procedures,
p. II:FoodAl 2).
A laboratory slide differs significantly from the environment of
the intestine. This is especially important when you realize that
fasting or abstinence from alcohol will alter intestinal villus
morphology and brush border membrane enzymes (Can J Physiol Pharmacol,
1985 Oct, 63:10, 1312-20) and that the combination of foods chosen
at a meal will alter transport properties of individual nutrients
due to changes in the composition of brush membrane lipids (Diabet
Res, 1991 Mar, 16:3, 127-38). These important changes in tissue,
enzymes, absorption and transport at the intestinal tract will not
be mirrored in a slide of blood taken from the arm or fingertip.
Additionally and perhaps most importantly, in response to in vivo
challenge of the gastrointestinal tract with a food, human beings
produce natural antibodies to dietary lectins such as soy, wheat
and peanut. These antibodies do not interfere with the agglutination
properties of the lectins but they are a significant part of our
immune repertoire (FEBS Lett, 1996 Nov, 397:2-3, 139-42). The in
vivo protection against any potential lectin-induced damage afforded
by such antibodies is not quantifiable or apparently observable
by in vitro microscopic analysis of agglutination, so an investigator
or technician would miss it. Analogously, if we saw a house ablaze
in a section of a city with closely-packed homes without knowing
there was a nearby and reliable fire department, we could erroneously
assume that an entire block of homes would go up in flames. This
is decidedly not the case in nearly every major metropolitan area.
Similarly, conclusions drawn about the impact of soy, peanut and
wheat lectins from observed agglutination on a slide without knowing
the extent of the innate protection our bodies generate in response
to these lectins are most likely mistaken.
"Leg Two" of the blood type theory addresses the effect
of foods on each blood type with regards to their interactions with
intestinal bacteria and the mucous secretions of the gut (the largest
source of blood type antigens other than red blood cells). This
is referred to as the "polyamine part". Polyamines are
chemicals which can be measured by a urine indican test. The urine
indican test, as employed by conventional labs and some natural
health doctors, does reflect bacterial activity in the small and
large intestines. Elevated levels of urine indicans are considered,
by some natural health care doctors, to be an indicator of "intestinal
toxemia" and "overgrowth of anaerobic bacteria" (Dirk
Powell, N.D. in A Textbook of Natural Medicine by Joseph Pizzorno,
N.D. and Michael Murray, N.D., Section II Supplemental Diagnostic
Procedures, p. II :Indic-1).
The conditions which, according to Dirk Powell, N.D., are confirmed
as resulting in elevated levels of urine indican are the following:
"inflammatory bowel disease, celiac disease, hypochlorhydria,
gastric ulcer, biliary & intestinal obstruction, jejunal diverticulosis,
scleroderma, gastrectomy, Hartnup's disease, pancreatic insufficiency,
diminished peristalsis and blue diaper syndrome". Urine indican
is recognized as valuable for detecting intestinal integrity, absorption
and protein catabolism (Jacobs et al, Laboratory Test Handbook,
Mosby, St Louis, 1984, p. 589). It is possible to draw oblique conclusions
about the impact of diet on colon health using the urine indican
test. The blood type diet theory hypothesizes, as stated on pages
27-8 of the book, that the urine indican test "shows that a
carcinogen entering your system is magnified to ninety times the
effect of someone for whom it is not toxic". There is no evidence
that we could find which substantiates this remark. Also, there
is evidence that enzymes such as intestinal transglutaminase, secreted
in response to certain lectins, repair lectin-induced damages to
the microvilli and gut epithelium (Biochem Biophys Acta, 1996 Nov,
1314:1-2, 66-70). In so doing these enzymes would inhibit and occasionally
eliminate the potential for the chronic intestinal inflammation,
bacterial overgrowth and illness ascribed to eating "wrong"
for your blood type.
"Leg Three" addresses the secretory differences with
regard to digestive juices (enzymes & acids) amongst the blood
types. On page XVI of the blood type book, it is explained that
higher than average stomach acid levels are to be expected in people
with blood type O. The tendency of this blood type to peptic ulcer
of the duodenum is cited as evidence of this. The book also notes,
on page XVI, that in the practice of the naturopathic doctor who
first coined the blood type theory it was observed that "type
O patients did well on animal products and protein diets --- foods
that require more stomach acid for proper digestion". It is
known that not all men and women of blood type O hypersecrete HCl,
a considerable percent secrete normal levels of stomach acid and
some hyposecrete stomach acid; peptic ulcer of the duodenum does
not have to be coincident with excess secretion of stomach acid
and the localized rather than diffuse histopathology of a peptic
ulcer of the duodenum cannot be explained as due to only excess
stomach acid secretion, something additional is adversely affecting
the duodenal health of patients so prone (McGuigan in "Harrison's
Principles of Internal Medicine" 13th edition & McKusick
in "The Principles & Practice of Medicine" by Harvey,
22nd edition). Dietary strategies for type O patients as outlined
by the blood type theory are intended, in large part, to treat people
who hypersecrete stomach acid. As we have explained this is often
not the case and such diet strategies will not be appropriate care
for quite a number of people who are blood type O.
More to our focus as regards "Leg Three", stomach acid
does not digest protein, pepsin does. On page 55 of the blood type
diet book it is stated that "type O's can efficiently digest
meats" (animal flesh)"because they tend to have high stomach
acid content". Hydrochloric acid is necessary for the conversion
of pepsinogen (inactive) to pepsin (active). Nonetheless it is pepsin
which is responsible for protein digestion, not stomach acid. The
optimum pH for pepsin's protein-digesting activity is 2.0, a gastric
pH consistent with what is realized by most non-doudenal ulcer patients.
When the pH of the stomach drops to below 2.0 and especially at
a pH of less than 1.5 (a pH more consistent with HCl hypersecretion)
pepsin becomes demonstrably less effective at digesting protein
(Lehninger, Biochemistry 2nd edition, p.196). Theoretically a person
who hypersecretes HCl would be less able to digest protein. Given
this, a "one size fits all" diet theory lumping every
blood type O person into a HCl hypersecretor/high animal protein
diet will not be health promoting.
A second aspect of the "Third Leg" of the blood type
diet theory involves the blood type variability in the secretion
of intestinal alkaline phosphatase. Blood type O and B secrete this
enzyme while its secretion is negligible in the other two blood
types. The blood type diet theory contends that intestinal alkaline
phosphatase is an enzyme whose primary function is to split cholesterol
and long chain fatty acids. On his website, the author of the blood
type theory has stated that intestinal alkaline phosphatase is "an
enzyme whose sole function is to break down dietary cholesterol"
(11/13/97 post at 07:17:24 by author to S. Shapiro). This is not
true. In the 1960's intestinal alkaline phosphatase was believed
to be involved in lipid absorption, due to its ability to hydrolyze
phosphate esters. In the 1970's reports suggested a different primary
function for intestinal alkaline phosphatase, namely, that it is
involved in calcium absorption (Gastroenterology, March 1972 62:3,
P. 452-8). Observations by the researchers Norman and Hanssler independently
confirmed a two to three-fold increase in intestinal alkaline phosphatase
activity after vitamin D administration coupled with a rise in calcium
transport. Recently intestinal alkaline phosphatase has been shown
to also play an important role in thiamin transphosphorylation (Arch
Physiol Biochem, 1995 Apr, 103:1, 33-8) and the hydrolysis of FMN
and FAD in addition to being involved in riboflavin transport (Int
J Vitam Nutr Res, 1983, 53:1, 109-14). At the very least intestinal
alkaline phosphatase is involved in much more than the function
heralded by the blood type theory. The possible significance of
its varying secretion re: blood type to an involvement in cholesterol
metabolism is overemphasized by the blood type theory to support
an unhealthy recommendation for cholesterol-laden animal proteins.
In our opinion, the blood type theory of diet doesn't have a leg
to stand on.
Deirdre B. Williams, N.D.
John J. McMahon, N.D.
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