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reader comments: blood type diet

31 March 2011

Although I do agree that Dr. (Peter) D'Adamo may be over-emphasizing the blood type diet in order to promote his products (i.e. supplements, books, etc.), I feel like he (and another doctor I looked into) state things that may not be new scientific discoveries, but they make sense, like type Os having more stomach acid and therefore can have a diet that's high in red meat.

reply: Why does this "make sense"? Wouldn't you want to see some scientific evidence for such a claim? Where is the data that shows that people with type O blood have an excessive amount of stomach acid? Where's the chart showing that a large random sample of people with different blood types shows that other blood types don't have as much stomach acid as people with type O blood? And where is the evidence that stomach acid determines how much red meat a person can eat? What does "high" mean in this context? For all you know, how much stomach acid a person has is not related to what blood type he or she is. We need to establish that before we worry about how much red meat to eat. Anyway, just because you can eat a diet high in red meat doesn't mean you should.

There is another doctor, Dr. Lam who has a similar viewpoint and includes a food chart with explanation as to why this specific food isn't suitable. http://www.drlam.com/blood_type_diet
As far as type Os, and the explanation that Dr. Lam provides, he states that type Os don't handle wheat/gluten well. Maybe there's a correlation to celiac's disease and blood type which in turn would explain why type Os should avoid gluten.

reply: Anybody can say anything, I suppose, but wouldn't you want to see the evidence? Where is the reference to the scientific studies that show that type Os don't handle wheat/gluten well? Where is the evidence that people with other blood types don't have problems with wheat or gluten? Do you really accept, without proof, that many people with type O blood have no problems with wheat or gluten?

Likewise for the notion that there might be some connection between celiac disease and blood type. Where's the evidence?

I understand that there are generalizations and exceptions and what not, but you have said that the diet may even be beneficial.

So is the only issue you have with these findings is the correlation that is made between blood types and what food to eat? And if so, then the diet probably would just be a good general diet to follow for health improvement purposes right?


reply: There are no "findings" by D'Adamo. He makes claims without scientific evidence to back them up. Dr. Lam asserts things like "Type As are prone to cancer, heart disease, and diabetes." Where's his evidence? Are you ready to accept his word and implication that other types aren't prone to these diseases? Where's the data that shows people with type A blood have significantly more bouts with cancer, heart disease, and diabetes? Demanding to see the evidence isn't cynical: it's what any reasonable person should do who cares about his or her own health.

By the way, I've looked around for some evidence for these claims about blood types and allergies or diseases. So far I haven't found any scientific evidence to back them up. If you find the evidence for any of these claims, let me know and I will pass it on.


13 Oct 2010
First let me say that I believe the role of the skeptic is critical in life, especially in this modern world where technology can be utilized to make anything seem true. So, unlike some of your detractors, I appreciate your efforts.

reply: Thank you. Technology is not the only thing that can be used to make the false seem true. Even reason, evidence, logic, and peer reviewed journals can be misused to mislead us.

That being said, NOTHING is more important than results. Not even elusive so-called 'truth.' If, ultimately, a diet improves one's health, even in a roundabout way (especially with the fact that America's nutritionist battalions are completely in the pocket of special interest groups and are therefore useless) the diet is valid.

reply: Results matter, of course, when it comes to dieting for health reasons. But there are other things to consider before giving credit to a particular diet for the results one is happy with. One can be right about the results being good but wrong about giving credit to a particular diet. Just because the results came after one went on the diet, it doesn't follow logically that the diet caused the results. Human physiology and health are enormously complex; each body and its environment has its own unique issues. There may be other factors involved such as other interventions besides the diet that one has introduced or the natural end to an illness or disease that coincides with the timing of the diet. Also, diets can be looked at for what they include and what they exclude. A dieter has no way of knowing, unless she does some controlled experiments, which, if either, is a significant causal factor in the improvement in health. For these reasons, it is necessary to do controlled studies to establish the efficacy of diets, whether for weight loss or for improvement in health. Personal experience matters, of course, but it is much more likely to be misleading than a well-designed scientific study. I'm not saying that scientific studies can't be misleading. They often are. For example, a study might find a correlation between taking some vitamin and a lowering of blood pressure or the colon cancer rate among women over 50, but correlation does not establish causality. Many correlations in scientific studies are spurious. That is, they are flukes and even though they have statistical significance, they do not represent the establishment of a causal connection.

The fact is that nutritional technology and 'knowledge' have not done a thing to make Americans healthier. So could it make sense that if progression is killing us, that regression could actually cure us? I believe so.

reply: Do you think our longer average life span is not due in large part to our progress in knowledge about health? The sailors who suffered from scurvy because of lack of vitamin C benefited greatly from the knowledge that they need this vitamin. The poor folks who suffered goiter and other diseases from iodide deficiency have benefited greatly from knowledge and technology (that makes adding iodine to salt, for example, possible). This list could go on for a very long time. If Americans aren't healthier it's not because the knowledge and technology to make them healthier hasn't done anything. What is that saying about leading a horse to water?

I'm not sure what you mean about progression and regression here, but I take you to mean that scientific knowledge is progress and the blood type diet is regression. In any case, it is a non sequitur to conclude that the blood type diet will cure us because science hasn't.

What could be a more specific customization of diet than what your own DNA developed from being exposed to? Regress to what YOUR ancestors developed eating. Dr D'Adamo's research is fascinating to me because it continually proves to me, year after year, in the laboratory of my own body, that is its truth. When I picked up ER4YT on the table at the bookstore, I was about 5 years into a diagnosis of some pretty strong food allergies. Of the 23 foods I tested allergic to, much to my amazement, every single one was an 'avoid' for my type. The odds of that being random are pretty slim.

reply: Starting with your last claim in this paragraph: actually the odds are pretty great that the list of foods to avoid would be similar. There are thousands of fad diets, many based on sympathetic magic, that advise people to avoid such things as wheat and grains, corn, dairy products, anything white or processed (sugar, salt, flour), anything dead, etc.

Regarding your testing allergic to 23 foods: Food allergies are rare (fewer than 5% of Americans have food allergies). Many people are misdiagnosed with food allergies. They may have food intolerances. William Meller, MD, has some very good information on the difference:

"An allergy is an overactive immune response to common substances, such as a bee sting, pet dander, or pollen. Some foods and medicines can also trigger allergies." According to Meller, most people who think they have food allergies actually suffer from food intolerance and do not involve the immune system at all. Fewer than 5% of Americans have food allergies, although 30% think they are allergic to some food or other. What's the difference between a food allergy and an intolerance? As noted, the former involves an overactive immune system; the latter isn't immune related.

The immune system doesn't forget. If you're allergic to something, the antibodies that were created by your immune system to attack what it responded to as a threat will always be activated when the allergen is present. "Once you are allergic to something, you will always be allergic to it." Also, allergy symptoms are limited: "red and itchy eyes, stuffy nose, sneezing and wheezing, hives, very rarely swelling of the intestinal lining." Unfortunately, many of these symptom are also the symptoms of a common cold. "The point of most of these symptoms is to try to expel the offending allergens from the body by crying, sneezing, coughing, or flushing it out." Other symptoms of allergies include itchy mouth, lowered blood pressure, faintness, a tightening throat, and trouble breathing.

I Can’t Eat That. I’m Allergic by Gina Kolata also addresses the issue of overdiagnosis of food allergies.

As to your point about the attractiveness of D'Adamo's idea of dieting like your ancestors allegedly did....well, you don't need to tell me that the idea is attractive....obviously it is and that is why his book is popular and why I wrote my entry in response to it....

So I bought the book. I followed his diet, not so much for weight loss but for health gain. I could be a poster child for this diet. Everything he says about my type end[ed] up being true. Including the workout recommendations. I have been on many diets and I take them seriously, but nothing has been as beneficial as following this diet. I even ignored several recommendations, owing to preferences (namely wheat and dairy), and have eventually had near collapses of my health as a result.

reply: Yes, you and many others have found after they followed this diet regime their health improved. I never question the claims of people that one thing followed the other. My questions are always about the logic of assuming the first thing caused the second and the explanations given as to how the first thing caused the second. Personal experience isn't infallible. Neither are controlled scientific studies. But the odds that one's interpretation of personal experience involves self-deception increase dramatically when (a) there is no plausible mechanism by which the alleged causal event occurs, and (b) controlled scientific studies don't support one's interpretation.

So you can bicker about stomach acid and lectins and fucose [fructose?] with other NDs, DOs, MDs and PhDs, but no one in America is offering as much bang for your diet buck as Peter D'Adamo. Certainly not the completely broken and alarmingly embarrassing 'nutritionist' contingent.

reply: I agree that there are many people calling themselves experts in nutrition who don't know what they are talking about. I've even written about some of these characters, e.g., Gillian McKeith. I'm afraid, though, that I consider Peter D'Adamo in the same class as "Dr." McKeith. (If you want good advice on nutrition, see a registered dietician.)

The people who I personally know that have been helped with some even life-threatening illnesses, or misdiagnoses, is a list that grows every year. Diabetes. Obesity. Intracranial hypertension. Crohn's/IBS. MS. Migraines. Arthritis. Intractable gastric reflux. Asthma. Heart palpitations. Food allergies. Eczema. Breast cysts. Thyroid disease. Narcolepsy. Central sleep apnea.

reply: "Helped" is not a very specific medical term, but I would like to see the scientific studies that support the claim that a blood-type diet had any special effect on diabetes (which affects people of all blood types, by the way), etc.

This is an awesome diet. There isn't one speck of it that is 'dangerous' despite allegations. Be a skeptic but don't, through your need to be right, keep people from trying something that could literally save their lives. That's just mean and selfish.


Jennifer Hul

reply: I'm glad you like the diet. I quote from the entry on the blood-type diet:

Since the diets developed by Peter are not  intrinsically harmful in general, it would be surprising if he couldn't find many satisfied customers willing to testify on his behalf. All he has to do is ignore all the cases he didn't help with his diets to make his case seem stronger than it really is. Even a broken clock is correct twice a day.

Some of Peter D'Adamo's dietary advice could be harmful, however. As Dr. Klaper notes: "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.'" Lactase-deficient readers who follow this advice are likely to end up with "severe bouts of abdominal cramps and diarrhea."

I don't call the diet dangerous, but there are many things that aren't dangerous that I still wouldn't recommend. I must politely reject your claim that this diet is saving lives and that I am being mean and selfish by advising people that the diet is pseudoscientific and contrary to most of what we know about human physiology and nutrition. One of the toughest nuts to crack is the "personal experience nut." The fact that scientists and the media often make exaggerated claims for scientific studies, observational and controlled, makes the nut all that much harder to crack.


3 Dec 2009
You have no room to be criticizing Dr D'Adamo's work with blood types and disease.  You have a PhD- very impressive.  Dr D'Adamo has been practicing medicine in his clinic for more than 20 years, and has watched tens of thousands of patients heal on his nutritional plan.  I have a library of research that I keep on hand, mostly from PubMed, that backs up everything Dr D'Adamo says. 

You can find dozens of articles on MEDLINE that review the blood type specificity of lectins found in fruits, nuts, fungus, and animal flesh. 

I find it sadly disturbing to hear "professionals" yammer away about Dr D'Adamo's "pseudoscience", while contributing nothing themselves to the art of healing. The science is there. The research is clear. If you don't believe me, I can send you a DVD. Either way, Robert, I hope you will learn to have more respect for those who are changing lives, as opposed to filling them with doubt. 


Eric Morrison

reply: D'Adama is a naturopath. To say he practices medicine is a stretch. Also, I notice on your website that you write: But most importantly, your personal story with the Blood Type Diet is what matters!

You say you have a library of research from PubMed to back up the blood type diet claims. Bring it on. I searched MEDLINE and didn't find any articles on the blood type diet, but I did get a link to a Mayo Clinic article by Katherine Zeratsky, R.D., L.D. who writes:

Some research suggests that people who have certain blood types may develop specific patterns of food allergies. However, there's no scientific evidence to support the so-called "blood type diet," in which different diets are recommended based on a person's blood type. At this time, eating or avoiding certain foods according to your blood type isn't thought to have any favorable influence on weight or overall health. In fact, a "blood type diet" may not meet your nutritional needs.

I also found an interesting website where Dr. Arpad Pusztai is asked about the use of his data on lectins by Adamo. You should find it disturbing to discover that your hero is misusing the data:

Yes, I know that D'Adamo refers to this Table and everything in it is true. However, it is a general Table in which not everything is valid in all species.

Most of our work has been done in rats as you know in which, obviously, no human blood groups are expressed.

As I said a number of times before very few lectins recognise and react with human ABO blood group sugar structures specifically. If anyone takes the trouble to go through all the entries in our book it ought to be plain to them that most lectins are not strictly blood group specific. They may react with the blood group epitopes, but not specifically.

For example, the main human B blood group determinant is galactose and obviously all galactose-specific lectins will react with it. However, as 95% of all galactose-specific lectins will also react with N-acetylgalactosamine that is the determining sugar in blood group A, these lectins cannot be human blood group specific. I hope this is clear. As far as I am concerned there is some truth in what D'Adamo says but the whole situation is far more complex than he or others can imagine.

The method you and D'Amamo espouse — intuition and anecdotes give you your base, then you look for any kind of scientific work that others have done and try to use it to confirm you bias — is not the best method if what you seek is the truth.

Eric Morrison replies [The whole reply is too long to reproduce here, so I've excerpted key points. Eric lists hundreds of published scientific papers as evidence for his position. RTC]

....You'll remember from your undergraduate physiology class that gastrin is the hormone that stimulates the production of hydrochloric acid and pepsinogen in the stomach, which work together to make pepsin. Pepsin is the enzyme that breaks down protein. So if these studies are showing that type Os make more pepsin, it would make sense that Os do better to eat meat than As.

reply: No, it wouldn't. Almost every food contains protein: nuts, peanut butter, seeds, beans, lentils, soy products (tofu, soy milk, tempeh), grains (wheat, oats, rice), eggs, vegetables (a cup of broccoli has 4 grams of protein), and dairy products all are good sources of protein.

As long as As make enough pepsin to break down whatever proteins they ingest, there is no need for As to cut out or cut down on meat.  It would be absurd to assume that everyone with type O produces plenty of gastrin or that everyone with type A doesn't produce enough to warrant eating meat as a primary source of protein. There may be good reasons for eliminating meat (or dairy products or other types of food) from one's diet, but blood type isn't one of them.

Another one of the founding discoveries made by Peter D'Adamo during his time in medical school was that Os had a significantly higher rate of peptic ulcers, while As had more stomach cancer. Believe it or not Bob, our beloved Dr D'Adamo didn't exactly believe in his father's ideas about blood type dieting either. He was convinced when he did the research and found astonishing correlations to blood types and diseases.

reply: It may be true that Os have more ulcers, but these ulcers are caused by bacteria and are not related to diet. As may have more stomach cancer and stomach cancer may be related to diet, but it is a logical leap to claim it is because As don't eat the A-type diet that they have more stomach cancer. Just because blood type and diet correlate to different types of cancers does not imply that the blood-type diet would have any effect on the ABO cancer rates. What you need to produce is a long-term study of a large random sample of people who have followed the blood-type diets so you can compare their cancer rates to the general population of ABO types.

It's true that certain groups of people, due to their evolutionary history, share a common blood type. Many people with the same evolutionary history have remained in the same geographical area for millennia. In some of those areas, certain types of cancers or other diseases may be significantly greater than in other geographical areas. It may also be true that diet is a significant factor in the development of certain cancers or diseases. But it doesn't follow from this data that blood type is a significant causal factor in the development of any of these cancers or diseases or that the dietary factors that may influence these illnesses has anything to do with blood type.


I bet you didn't know that foods also have blood type, Mr. Carroll. Your blood type is just a small piece of sugar that sits on the outside of your cell. If your sugar is fucose, that makes you type O. If it's fucose covered in N-Acetyl galactosamine, you're type A. If it's fucose covered in D-Galactose, you're type B. Your body makes antibodies against whichever of these sugars you don't produce on your own, which is why a wrong transfusion can kill you. The antibodies clot the sugars together, meaning your immune system has a better chance of doing its job. This part is common sense. If you introduce antigens in your blood stream that you make antibodies against, your body will reject them. So if you're type O or type A and you drink milk, you're absorbing the D-galactose from the milk, which your blood type naturally opposes.

reply: As you remember from your undergraduate nutrition class, mammalian milk contains lactose which in turn is made up of D-galactose and D-glucose. If I suckled at my mother's teat, I ingested D-galactose no matter what her blood type was. By your logic, no human with type A blood should drink breast milk, a position I find a bit at odds with the data.

Anyway, I'm type A and have been drinking cow's milk for over 60 years with no obvious adverse effects.

As you remember from your undergraduate pharmacology class, dose makes all the difference. The amount of D-galactose in pasteurized cow's milk isn't going to harm me any more than the D-galactose in my mother's milk harmed me as an infant.


Lectins are proteins found in foods that can cause a number of problems in the human organism. It wasn't Dr D'Adamo that discovered them either; it was Hermann Stillmark of the University of Dorpat in 1888-- the one that discovered the poison Ricin, which is a lectin from castor beans. Then in 1908 Karl Landsteiner, who discovered ABO blood types, noticed that lectins from lentil beans would clot together rabbit red blood cells, without doing anything to pigeon red blood cells. It was then William Boyd of the Boston University School of Medicine who found that lectins are blood type specific. For example, he discovered that lima bean lectins clotted together type A blood cells, but not type O cells....A "considerable amount of work" has been done on the study of lectins. They are known to bind together red blood cells, and their blood type specificity is no secret.

reply: My editor, John Renish, notes that the assassin who killed Bulgarian dissident Georgi Markov in 1978 by injecting him with ricin didn't need to know Markov's blood type.

You should note that lectins can also serve very important and useful biological functions. Anyway, I'll quote Dr. Pusztai again:

....very few lectins recognise and react with human ABO blood group sugar structures specifically. If anyone takes the trouble to go through all the entries in our book it ought to be plain to them that most lectins are not strictly blood group specific. They may react with the blood group epitopes, but not specifically. For example, the main human B blood group determinant is galactose and obviously all galactose-specific lectins will react with it. However, as 95% of all galactose-specific lectins will also react with N-acetylgalactosamine that is the determining sugar in blood group A, these lectins cannot be human blood group specific.

Also, just because lima bean lectins clotted together type A but not type O blood cells in vitro does not mean that lima beans should or shouldn't be eaten by various blood groups. My mother used to serve lima beans on a regular basis. I loved them and never suffered any ill effects from them.

You see, this is why it amazes me that people still don't believe Dr D'Adamo's work is based in science. You have to try hard not to realize how much research has gone into his work.

reply: I call D'Adamo's work pseudoscience rather than science not because he doesn't cite scientific papers to support his beliefs. He does. But he misinterprets the data and draws inferences that are not justified from the data. He also cannot point to a single RCT or prospective study that demonstrates any of the claims he makes about the ill effects of not adhering to a blood type diet and the beneficial effects of following a blood type diet. He cherry-picks scientific studies and makes unjustified assertions based on those studies.

No, the Blood Type Diet is not accepted by the majority of mainstream medicine. I understand that; yet, AMA acceptance should not be a meter of medical magnitude.

reply: I agree. AMA acceptance is irrelevant to the value of the blood type diet, but so is the listing of dozens of studies that support completely different points from those made by D'Adamo. Also, for the record, my editor John Renish tells me that "the AMA has only about a third of all physicians as members and is primarily a lobbying organization, rather than one that controls the practice of medicine. Its only tie to questions like blood-type diets is that its journal has an independent editorial staff that accepts only about 10% of all papers submitted for publication."

There is one medical doctor who summarizes it best:

"When I first heard of Peter D'Adamo's blood group diet, of course I was very skeptical: Should we have missed in our book (Prokop/ Uhlenbruck: Human Blood and Serum Groups) such an important aspect? But years later, my interest switched to the nutritional field while working on the so-called metabolic syndrome, my interest increased in studying the role of genes in metabolic processes. I found out, that Peter D'Adamo's blood group orientated diet could probably be a first step in the right direction. I am afraid that Peter's merits are not estimated enough in the scientific world. Therefore it seems to me necessary, not only to promote his concept here in Europe, but also to tell him that I acknowledge him as one of the most creative scientists in the Western world."

- Professor Gerhard Uhlenbruck, PhD, MD Director, Institute for Immunobiology, University of Cologne

If you wish to play the quote game, I can find thousands to support my side. But this isn't about feelings or beliefs, right? I don't think it comes down to which respectable physician has a stronger opinion, because that's not scientific. If you wish to cherry-pick your sources, that's fine. Feel free to pick through this modest list. You wanted me to "bring it on", so here you go.

reply: I won't post Eric's list, but it is so long that if I spent every waking moment reading his references I would have to live another twenty years to complete the task. Here are three chosen randomly:

Greer F, Pusztai A Toxicity of kidney bean (Phaseolus vulgaris) in rats: changes in intestinal permeability. Digestion 1985;32(1):42-6

Mourant AE Blood Types and Disease Oxford university Press 1979

Visek WJ Arginine needs, physiological state and usual diets. A reevaluation. J Nutr 1986 Jan;116(1):36-46

Finally, here is a page of responses to criticism about the Blood Type Diet.  If you've made it this far, then I must say I am thoroughly impressed.  I hope you will consider changing the tone on your website, giving credit where credit is due.  If you need any more research, I still have plenty.  http://www.dadamo.com/science_critic.htm



reply: When you add evidence of zero weight to supporting your point to tons of other irrelevant evidence, you will never reach a critical point where the quantity of your evidence transforms its quality. It may be true that kidney beans are toxic to rats, but that fact does not support the position that humans with blood type A, AB, or O should avoid kidney beans because they contain lectins. It may be true that blood types correlate with certain diseases, but that fact does not support the position that blood types are relevant to the development of those diseases. Blood type may be relevant as a marker for other genetic factors that are known to be causally related to those diseases, and diet may be a known relevant factor in the development of those diseases, but those facts, if they are facts, are a long way from proving that there is a correct diet for each blood type.

I fear this discussion could go on forever. You and the defenders of the diet see relevance where I don't. You see logical connections where I see logical leaps. You see valid inferences where I see non sequiturs. However, I will change my mind if I see the randomized control studies that demonstrate the claims of the blood type diet. These studies will randomly assign large numbers of people to various dietary groups. If long-term studies shows that the blood type diet is significantly superior to non-blood type diets in terms of preventing illness or in extending mortality, I'll get on your pony and ride it. In fact, if very large prospective studies where a large sample is taken from the general population and then correlations are sought between various diets and diseases, mortality rates, etc. — are properly done and strongly support your position (much teasing of the data would have to be done to eliminate artifacts, I would imagine), I'll join your club.

In the meantime, humans are omnivores. There may be good reasons why certain people should or should not eat certain foods. For some individuals, it may be the case that their blood type is relevant to how their body responds to certain foods. The idea that there is one type of diet good for people with type A blood and another for people with type O, etc. is preposterous on its face given the history of human evolution and development. To prove such a notion requires extraordinary evidence, not anecdotes and reams of irrelevant references.

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