Blood Type Diet: Fact or Fiction?
by Michael Klaper, M.D.

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, Type A's are docile vegetarians, and Type B's are dairy-eating omnivores - has become a dietary manifesto for many people. 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.

Author, D'Adamo hangs much of his theory on the action of lectins, which are sugar-containing 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 bestseller list, with the intent of changing the eating habits of a nation - I believe the author is obliged to present solid scientific evidence that supports that assertion. Author D'Adamo repeatedly fails to do, throughout the book. A statement that potentially will frighten millions of Type O readers about eating kidney beans, lentils, and wheat should be supported by photographs taken through a powerful (electron) microscope. These photomicrographs would show 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. (Sampling of muscle fibers, fat tissue, etc., is a common, safe, and virtually painless technique, known as "skinny needle" biopsy, and is routinely performed on paid volunteers by researchers in nutrition, exercise physiology, pharmacology, aging, and other sciences.) The photographs would clearly show the lectin deposits in the muscles of people with Type O blood - and little or no deposits 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 his own research or cite other scientific studies wherein tiny microelectrodes that measure acidity inside the cells were inserted into the muscles of paid human volunteers of various blood types. All subjects would be fed a meal of lentils and kidney beans, and a significantly greater shift towards alkalinity would be observed in the muscles of the Type O subjects. Yet, no such studies are cited or 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 away from eating high-protein, high-fibre legumes and other potentially valuable foods? Indeed, it may be best for a particular person not to eat a particular legume - but the reason he or she should refrain from doing so should be for solid nutritional/medical reasons - like true allergies, colitis, etc. - and not because of their ABO blood type.

D'Adamo's book contains many scientifically unsatisfying, "one size fits all" statements, like that on page 63, "Type O's do not tolerate whole wheat products at all." Such a statement prompts the question, "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 digestive or other problems when they eat wheat. They do indeed, but the reason is because they have a true wheat allergy, 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 with colitis, 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 and who rely on breads as a major source of energy and protein - 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 photomicrographs 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 people who had recently ingested wheat and 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 makes two hard-to-believe statements concerning dairy products - one which made me doubt his understanding of basic science, and another 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 would have to 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.

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 the author 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. 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.

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 the author 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, for that matter, to long-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 - microscopic capillaries so narrow that the red blood cells must line up single file to get through. If the red blood 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 blood stream will be prevented from delivering its life-sustaining cargo of oxygen and nutrients to the tissues served by those obstructed capillaries. Cells deprived of oxygen become damaged, and soon 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's eating wheat, Type A's 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 vital capillary beds in your heart, lungs, kidneys, brain, eyes, and other essential organs are subjected to barrage after barrage of agglutinated red blood 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 and destruction - with eventually many micro-infarctions scattered throughout these vital structures. Over time, the brain, heart, lungs, kidneys and adrenals would be irreparably scarred and fibrosed by these processes - resulting in multi-organ failure and 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 pathology literature. No pathologist I know has ever mentioned tissue infarction from lectin-induced red cell agglutination as a cause of any disease in humans.

I found especially disturbing in Eat Right for your Blood Type author D'Adamo's portrayal of people of vegetarian persuasion. 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 portrays 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." (How does he know Adolph Hitler's blood type?) D'Adamo's system seems to create a "blood type astrology" ("What's your type? O Positive? I knew it! So am I!") that imposes strange, limiting stereotypes on very complex human beings.

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)?

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.