Blood Type Diet: Fact or Fiction?
Michael Klaper, MD
|For a good video explanation
of why this diet is "fiction", watch this.
while Type B's
are dairy-eating omnivores has become a manifesto for many
people to rationalize including regular portions of meat and other
animal products in their diet. ("After all, my ancestors did it.")
However, the "blood type diet" theory, and the book that promotes
it, presents many problems that prevent me from seriously basing any
of my dietary choices upon them.
"blood type diet" theory has gained widespread attention from
the public since the release of "Eat Right For Your Type" by
Peter J. D'Adamo, N. D. (G. P. Putnam's Sons, New York, 1996).
The book's basic premise that Type O's are the dominant,
hunter-caveman type that require meat in the diet, that Type
A's are docile vegetarians,
One of the book's
most disturbing characteristics is the frightening images that the
author calls forth without providing scientific documentation. For
example, D'Adamo hangs much of his theory on the action of lectins,
proteins found on the surface of certain foods that can cause various
molecules and some types of cells to stick together. He blames lectins
for serious disruptions throughout the body, from agglutination
of the blood cells to cirrhosis and kidney failure (page 24). On
page 53, D'Adamo states that, "...certain beans and legumes, especially
lentils and kidney beans, contain lectins that deposit in your muscle
tissues, making them more alkaline and less charged for physical
activity." This is quite a serious scientific charge, and an alarming
thought if you are blood Type O namely, that after eating
a bowl of bean chili or lentil stew, lectin proteins are depositing
in your muscles and altering their function, changing their acidity,
and diminishing your capability for physical action.
If one is going
to make a statement like that and publish it in a book destined
for the New York Times bestseller list and intended to change the
eating habits of a nation I believe the author is obligated
to present solid scientific evidence of supporting their assertions,
which D'Adamo repeatedly fails to do. If an author is going to frighten
millions of Type O readers about eating kidney beans, lentils, and
wheat, I think they are obligated to provide verifiable evidence.
To begin to convince me of the existence of his "lectin gremlins,"
he would have to publish photographs, taken through a microscope,
of muscle tissue biopsied from people with Type O, Type A, Type
B, and Type AB blood after they have eaten kidney beans and/or lentils.
The photographs should clearly show the lectin deposits in the muscles
of people with Type O blood and not in the tissue samples
from the muscles of people with Type A blood. If an author cannot
produce proof like this, or clearly cite the scientific references
in the text where other people have demonstrated such proof, his
credibility, to me, is severely diminished. D'Adamo presents neither
photos nor corroborating studies to support his speculations.
the assertion that lectins change the muscles, "making them more
alkaline and less charged for physical activity," the author would
need to publish or cite studies wherein microelectrodes that measure
acidity inside the cells were inserted into the muscles of people
of various blood types. After they all ate a meal of lentils and
kidney beans, if D'Adamo is to be believed, a significantly greater
shift towards alkalinity should be seen in the muscles of the Type
O subjects. Yet, no such studies are presented. If an author doesn't
have this kind of proof, is it responsible for him to make statements
that may frighten millions of people from eating high-protein, high-fibre
legumes and other potentially valuable foods? It may indeed be best
for a particular person not to eat a particular legume but
they should do so for solid nutritional/medical reasons (allergies,
colitis, etc.) independent of their blood type.
pushes the "blood type" theory beyond the limits of believability
for me is the primary mechanism of physiologic damage that D'Adamo
postulates namely, lectin proteins on some foods causing
blood agglutination in certain people of blood types who are "not
genetically/evolutionarily suited" to eat those foods. This is a
very serious and potentially life-threatening phenomenon
that he proposes. Agglutination means that the red cells in your
bloodstream are irreversibly sticking together and forming clumps.
Once they begin to clump together, they don't come apart. (Note
that this is very different than blood sludging, or so-called rouleoux
formation a phenomenon seen when the surface of the red cells
become coated with fat or other substances to make them sticky enough
to temporarily and reversibly adhere to each other's surfaces
but not to become permanently bonded through irreversible intertwining
of surface proteins, which is what happens in agglutination.) Having
your blood agglutinate as it circulates through your body is not
conducive to good health or to long term (or short term)
What is so bad
about little clumps of red blood cells sailing through the bloodstream?
Red blood cells deliver oxygen to the cells of vital tissues like
the brain, heart and kidneys. To accomplish this delivery, they
must flow through the tiniest of blood vessels capillaries
so narrow that the red blood cells must line up single file to get
through. If the red cells are being agglutinated by lectins or anything
else, clumps of red cells will clog up the capillaries and block
the blood flow. Thus, the bloodstream will be prevented from delivering
its life-sustaining cargo of oxygen to the tissues served by those
capillaries. Cells deprived of oxygen become damaged, and eventually
die (cell death is called "infarction" of tissue.)
Since most people
are unaware of their blood types, let alone what foods are "evolutionarily
inappropriate" for them to eat, it is reasonable to assume that
on most days most people eat the "wrong foods" for their blood type
(e.g., Type O eating wheat, Type A eating meat, etc.). Thus, according
to D'Adamo's theory, most everyone experiences repeated showers
of agglutinated red cells throughout their bloodstream after most
every meal day after day, month after month, year after year.
If the capillary beds in your heart, lungs, kidneys, brain, eyes,
and other essential organs are subjected to barrage after barrage
of agglutinated red cells, they will eventually begin to clog up.
These micro-areas of diminished blood flow would at first cause
scattered, then more concentrated areas of tissue damage
with eventually many micro-infarctions scattered throughout these
vital structures. The brain, heart, lungs, kidneys and adrenals
would soon be irreparably damaged by these processes, resulting
in potentially fatal outcomes in millions of people.
Such a syndrome
of organ failures due to lectin-induced micro-infarctions of the
brain, heart, kidneys, retinas, and adrenals would be well known
to pathologists and other medical scientists. It would not be a
subtle disease. In the pathology texts, there would be clear descriptions
complete with photographs taken through high-power, optical
microscopes as well as electron microscopes of damage from
lectin deposits and blood agglutination in most major organ systems.
The existence and intricacies of such a widespread disease would
be as common knowledge among physicians and cell scientists as atherosclerosis
is today. Yet, I am aware of no such descriptions in the pathologic
literature. No pathologist I know has ever mentioned tissue infarction
from lectin-induced red cell agglutination as a cause of any disease
So when I read
a "one size fits all" statement like on page 63, "Type O's do not
tolerate whole wheat products at all," I have to ask, "What does
he mean, 'at all'?" Do Type O's eat a whole wheat cracker and fall
on the ground holding their abdomen and vomiting or worse
yet, suffer immediate brain damage due to their blood cells agglutinating
throughout their brain? How much wheat can a Type O eat before their
blood agglutinates? One hamburger bun? One noodle?
I'm not denying
that many people do experience problems when they eat wheat. They
do, but they do so because they have a gluten intolerance, or some
other verifiable mechanism not because of some sugar and
protein molecules sticking up from the surface of their red blood
cells. Like D'Adamo, I grant that wheat can be a problematic food
for people, and I often recommend eliminating it from the diet.
Lectins may even play a role in the inflammatory process for some
people. However, before one tells millions of individuals with Type
O blood to never eat whole wheat many of whom apparently
have no difficulty with whole wheat isn't some convincing
scientific proof required? I feel that author D'Adamo at least owes
his readers a text citation with supporting evidence that wheat-induced
colon dysfunction is a condition peculiar to Type O's. Yet, his
text is devoid of scientific endnote citations.
me, he would need to show me photographs of intestinal tissue from
Type O people who have recently eaten wheat and who clearly have
evidence of lectin agglutination clogging up the function of their
intestinal cells. I would also need to see pictures of tissue biopsies
from Types A, B, and AB whose intestinal walls are seen to be undamaged
and far less burdened with lectin deposits than those with Type
O blood. As far as I know, inflammation of the intestine, like colitis,
Crohn's disease, and gluten sensitivities, occurs in people of all
blood groups, not just Type O and D'Adamo cites no convincing
proof to the contrary.
also makes a few hard-to-believe statements concerning dairy products
two of which made me doubt his understanding of basic science,
and one that raises concerns about the safety of his nutritional
1. D'Adamo states
on Page 23 that, "If a person with Type A blood drinks it (milk),
his system will immediately start the agglutination process in order
to reject it." If he wants me to believe a statement like that,
he had best show me pictures of Type A blood cells under the microscope
agglutinating after the person drinks milk, wherein Type O and Type
B blood cells are shown not to agglutinate. He again shows no such
photos or other believable evidence of the phenomenon. D'Adamo would
also have to explain why Type A people who drink milk (sometimes-massive
quantities of it) do not suffer strokes and emboli as their blood
agglutinates throughout their vascular system. He presents neither
proof nor even plausible explanations for the above very
troubling in a book presented as "based on science."
2. A statement
that causes me great concern regarding the safety of D'Adamo's dietary
advice appears on page 37, where, despite widespread knowledge that
many non-Caucasians are intolerant of dairy products due to the
normal disappearance of lactase enzymes in their intestinal cells,
D'Adamo recommends that "Type B's of Asian descent may need to incorporate
them (dairy products) more slowly into their diets as they adjust
their systems to them." This seems like strange counsel from an
author trying to improve the intestinal health of his public. I
fear that the consequences for many of his unsuspecting, lactase-deficient
readers who follow such advice will be severe bouts of abdominal
cramps and diarrhea.
in this book that makes me not want to recommend it to my patients
is on page 53, where D'Adamo writes that:
called hypothyroidism, occurs because Type O's tend not to produce
enough iodine." The reality is that the body does not "produce"
iodine at all, any more than it produces calcium, magnesium, sodium,
or any other earth mineral. Iodine is a halogen element, related
to chlorine and bromine, which is taken up by plants from the soil
and in the sea which are then consumed in the diet [usually
not due to not enough in the soil - Don B.]. To worry tens of
millions of Type O readers that they "may not be producing enough
iodine" (which no one does) and are thus at risk for hypothyroidism,
is unfounded and, I feel, unnecessarily worrying. The causes of
clinical hypothyroidism are complex issues, probably involving autoimmune
and other mechanisms of injury to the thyroid tissue. To imply that
eating red meat and avoiding wheat (a "Type O diet") will help the
Type O person "produce iodine" is unsubstantiated and may not only
raise false hopes in the reader, but may also increase the risk
of meat-associated diseases.
Beyond the usual
association with heart attack, stroke, osteoporosis, colon cancers
and other degenerative diseases, animal-based diets foster the growth
of pathogenic organisms in the intestine, which can injure the intestinal
wall and lead to the "leaky gut syndrome" a condition of
increased intestinal permeability which allows injurious fragments
of antigenic food proteins and bacterial breakdown products to leak
into the bloodstream (1). These foreign, inflammation-inciting substances
can, in turn, exacerbate rheumatoid arthritis, lupus, and other
autoimmune diseases in tissues throughout the body (2). The bacteria
in the colons of people who consume vegan diets are far less likely
to cause these kinds of diseases (3).
the colon full of meat residue from a high protein diet has been
shown to be highly correlated with cancer of the colon among
the leading killers of industrial nations (4). In fact, animal protein
seems to be "high octane fuel" for the growth of many kinds of cancers
(5). I fear that the apparent improvement experienced by many people
who use the "zone" rationale to become big-time carnivores will
ultimately be at the cost of damaged vital organs and more lethal
and degenerative diseases.
Beyond his views
on biology, I was disappointed in D'Adamo's psychological portrayal
of people of vegetarian persuasion. In the book, he tells flesh-eating
Type O's that they have a "genetic memory of strength, endurance,
self-reliance, daring, intuition, and innate optimism...", "the
epitome of focus, drive...", "hardy and strong, fueled by a high
protein diet" (is he describing a Type O "master race"?), while
he paints the "more vegetarian" Type A as submissive tofu eaters,
"biologically predisposed to heart disease, cancer and diabetes"
(p. 97). He labels Type A's with personalities "...poorly suited
for the intense, high-pressured leadership positions at which Type
O's excel," (p.142), stating that, in pressure situations, people
with Type A blood "tend to unravel" and "become anxious and paranoid,
taking everything personally." Finally, on page 143, he saddles
the group with the dark image of Adolph Hitler, "...a mutated Type
A personality." D'Adamo's system seems to create a "blood type astrology"
("What's your type? O Positive? knew it! So am I!") that imposes
strange, limiting stereotypes on very complex human beings.
There is nothing
sacrosanct about the ABO blood typing system devised by Dr. Landsteiner
in the 1920's. It is only one system classifying more than thirty
proteins on the surface of cells that determine other blood groups,
with names like Auberger, Diego, Duffy, Kell, Kidd, Lewis, Lutheran,
MNSs, P, Rh, Sutter, and Xg. This means that food selections that
may be "right" for the ABO blood group system might be "dead wrong"
for someone's Kell or idd antigens. Why are we deifying the D- galactosamine-fructose
molecules on the red cell surfaces that determine ABO Type?
In my opinion,
D'Adamo has spun an evolutionary fairy tale that leaves many unanswered
questions. What exactly is he proposing happened to Type O hunter-gatherers
when the Type A people began growing wheat, barley and other grains?
Do Type O people eat a mouthful of barley and fall down in the dust,
unable to work and reproduce? Do they then become warlike and club
the agrarian people to death because lectins are clogging their
intestines? Do the genetic changes to Type A blood type magically
appear just before a society grows new grains (allowing them to
eat the new grains in the first place), or did Type A blood types
emerge after the grains are grown, as the people with Type O blood
died out from their blood agglutinating in their brains? And why
would so many of the native Indians of North America, classic Type
O hunters, go to the trouble of cultivating high-lectin corn (maize)?
Someone talk some science to me, please...
Beyond the "blood
type issue," perhaps a deeper question about any book which advocates
a meat-based diet for the majority of the population is, "In today's
world, is eating meat, in any form, safe?" It appears that to base
one's diet around animal foods is becoming a high-risk activity,
similar to unsafe sex or driving without wearing a seat belt. Consider
the smorgasbord of health hazards available at today's meat counters.
It's a safe bet that virtually every cut of "fresh" meat produced
commercially in North America today contains:
hydrocarbon pesticides and herbicides, linked to cancers and birth
antibiotics and growth-augmenting sex hormones fed to the animals
and stored in their tissues,
like the potentially lethal E. coli 0:157 and Salmonella bacteria.
(Hamburger roulette, anyone?)
specter of the brain-destroying prion protein, the cause of spongioform
encephalopathies "mad cow disease" in bovines Creutzfeldt-Jacob
disease, or CJD in humans. (I feel sadly certain that what occurred
in England with mad cow disease will probably occur here in North
America and other parts of the world within in the next two years.
I sincerely hope I'm wrong.)
ever-increasing risks connected to meat consumption, I fear that
the theories and books that attempt to justify and promote the eating
of flesh for whatever reason could be opening the
floodgates of ghastly epidemics five or ten years from now. These
plagues likely will have a magnitude that will dwarf everybody's
concerns about "being in the zone" or eating "right for your type."
If you find
all the foregoing questions as troubling as I do, perhaps you, too,
will want to think long and hard about adopting the "blood type"
diet as your guide for health-enhancing dietary choices.
Comments: I know many "Type O"
people who do far better on a plant-based diet than an animal-based
diet. In fact I don't know anyone who does better in the long run,
health-wise, on an animal-based diet. Also, when I first heard about
the blood type diet, and I wanted to know if it had any validity,
I wondered if other mammals had different blood types (especially
primates). For if they did, the fact that they eat the same diet
would tend to invalidate D'Adamo's claims. Well guess what? They
do have different blood types just as we do. Maybe they should consider
changing their diets too? Or maybe they're lucky that they can't
But there have been people who've done better when
they went back to eating animal products after eating a plant-based
diet for a goodly amount of time. At first blush, this would suggest
that those people do better with animal products in their diet,
but there's an underlying reason they did better, and it's not because
they required animal products. For an interesting explanation of
why they did better when they dropped their plant-based diet and
went back to eating animal, see this
article (particularly the section headed "Iodine
supplementation via animal products")
(1) a) Galland,
L. Intestinal Dysbiosis and the Causes of Disease. Journal of Advancement
in Medicine - Vol.6, No.2, Summer, 1993.
b) Inman, R.
Antigens, the Gastrointestinal Tract, and Arthritis. Rheumatic Disease
Clinics of North America - Vol. 17, No. 2, May 1991.
c) Katz, K.
Intestinal mucosal permeability and rheumatological diseases. Bailliere's
Clinical Rheumatology - Vol. 3, No. 2, August, 1989.
(2) a) Kjeldsen-Kragh,
J. Controlled trial of fasting and one-year vegetarian diet in rheumatoid
arthritis. Lancet, 1991; 338:899-902.
et al. Intestinal Mucosal Permeability in Inflammatory Rheumatic
Diseases. II. Role of Disease. (J. Rheumatol. 1991; 18:394-100)
(3) a) Peltonen,
R., et al. Changes of Faecal Flora in Rheumatoid Arthritis During
Fasting and One-Year Vegetarian Diet. British Journal of Rheumatology
b) Ling, W.
Shifting from a Conventional Diet to an Uncooked Vegan Diet Reversibly
Alters Fecal Hydrolytic Activities in Humans. Journal of Nutrition,
122: 924- 930,1992.
(4) a) Bidoli,
E. et al (1992), Food consumption and cancer of the colon and rectum
in North-Eastern Italy, International Jnl of Cancer v.50 p.223-229.
b) Rao, A V.
& Janezic, S A. (1992), The role of dietary phyosterols in colon
carcinogenesis, Nutrition & Cancer v.18 (1) p.43-52.
W C. et al (1990), Relation of meat, fat and fibre intake to the
risk of colon cancer in a prospective study among women, New England
Jnl of Medicine v.323 (24) p.1664-1672.
(5) a) Mills,
P. K. (1988), Animal product consumption and subsequent fatal breast
cancer risk among Seventh-Day Adventists, American Jnl of Epidemiology
v.127 (3) p.440-453.
b) Fraser, G.
E. et al (1991), Diet and lung cancer in California Seventh-Day
Adventists, American Jnl of Epidemiology v.133 (7) p.683-693.
to list of Articles