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The Blood Type Diet: Fact or Fiction?
by Michael Klaper, MD

For a good video explanation of why this diet is "fiction", watch this.


The "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,
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.

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.

To substantiate 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.

What finally 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) survival...

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 in humans.

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.

To convince 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.

Author D'Adamo 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 advice:

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.

Another assertion in this book that makes me not want to recommend it to my patients is on page 53, where D'Adamo writes that:

"This condition, 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).

Repeatedly packing 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:

Residues of hydrocarbon pesticides and herbicides, linked to cancers and birth defects,

Residues of antibiotics and growth-augmenting sex hormones fed to the animals and stored in their tissues,

Fecal microbes, like the potentially lethal E. coli 0:157 and Salmonella bacteria. (Hamburger roulette, anyone?)

The nightmare 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.)

Given these 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 read.

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") Don Bennett



(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.

b) Mielants, 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 1994; 33:638-643.

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.

c) Willett, 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.

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