A Collection of Strange Beliefs, Amusing Deceptions, and Dangerous Delusions

From Abracadabra to Zombies | View All

blood type diet

The blood type diet is based on the belief of naturopath James D'Adamo that one's diet should be determined by one's blood type. Like many self-confident mavericks before him, D'Adamo appealed to intuition for his brainstorm ("over the years, he recognized that each of the 4 blood types thrived on certain foods and physical activities") and anecdotes rather than controlled studies to support the validity of his ideas.  His son, also a naturopath, Peter J. D'Adamo (whom the rest of this entry is about) is a fruit that did not fall far from the tree. He has written several books, and travels the world promoting the blood type diet.

There is no reasonable scientific basis for the claim that blood type should determine one's diet, though Peter claims to have collected "over 1,000 scientific articles on blood types and their correlations to disease, biochemistry, nutrition, and anthropology."* Even so, he's never done a controlled study on blood type diets. Yet, he claims that blood type determines body chemistry to such an extent that those with type A blood should go vegetarian and meditate, those with type O should eliminate grains and do aerobics. He suggests similar unscientific diets for types B and AB.

The four human blood groups are defined by the type of glycoproteins — confections of sugar and protein — found on the surface of red blood cells and other cells.... A gene known as ABO helps construct these glycoproteins by ordering the placement of sugar molecules on a protein “backbone” called the H antigen. The pattern formed by these sugars determines whether an individual’s blood type is A, B, AB, or O. (In the O type, no sugars are attached to the antigen.)--Harvard Science

According to Michael Klaper, M.D.,

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....

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.

Peter D'Adamo's reasoning is based on speculative inferences from such "facts" as that type O is the oldest blood type. It isn't. A is the oldest blood type. Studies in humans, chimpanzees, and bonobos show that alleles coding for blood type A are the most ancient version of the ABO blood group. This trait was shared prior to the evolutionary split between chimpanzees and hominids five to six million years ago. B blood type split from A about 3.5 million years ago and O blood type split from A about 2.5 million years ago. From this error regarding the age of type O, D'Adamo reasons that people with type O blood should eat the kind of diet the earliest humans ate: one rich in fat and protein.

"Group A [D'Adamo erroneously claims] is the second oldest blood group, appearing around 25,000 - 15,000 B.C., when larger human settlements first appeared as farming developed."* From this "fact," D'Adamo infers that people with type A blood should eat their veggies.

One problem with D'Adamo's reasoning is that agriculture developed independently in different parts of the world, the earliest settled communities didn't develop agriculture for many centuries in some cases, and the developments weren't all positive. "A typical hunter-gatherer enjoyed a more varied diet and consumed more protein and calories than settled people, and took in five times as much vitamin C as the average person today" (Bryson: 2010). Worse: "Rice inhibits the activity of Vitamin A; wheat has a chemical that impedes the action of zinc and can lead to stunted growth; maize [corn] is deficient in essential amino acids and contains phytates, which prevent absorption of iron" (Bryson quoting John Lanchester). According to Bryson, the average height of people fell by almost six inches in the early days of farming in the Near East. (Hey, but it was all organic!) Clearly, diet matters, but blood type isn't a very good guide to what diet is right for you.

Group B, D'Adamo erroneously claims, "emerged between 15,000 and 10,000 B.C. as tribes migrated from Africa to Europe, Asia and the Americas and mingled with other populations."* So, concludes D'Adamo, people with type B blood should eat a "balanced diet." In fact: "All human ABO blood types existed as of several million years ago. From the time of the earliest humans, all ABO types existed as hunter-gatherers until the advent of agriculture."*

Of course, even though there is no plausible scientific connection between blood type and a proper diet, the advice D'Adamo gives on what foods to eat or avoid can still be helpful to many people. The success of his books indicate that the diets he proposes are probably healthy and safe for most people.

Blood type has little to do with digestion or body chemistry. If you have blood group A, then you've got A antigens covering your red cells and anti-B in your plasma. Antigens are substances that evoke an immune response. Since people in blood group B have B antigens and carry anti-A in their plasma, type A blood should not be given to those in Group B, and vice versa. (Group O has neither antigen and group AB has some of each.) Furthermore, about 85% of us, regardless of blood type, carry the Rh antigen, while about 15% are Rh negative. About 90 to 95 percent of African Americans and 98 to 99 percent of Asians are Rh-positive.* Also, since pathologist Karl Landsteiner identified the four blood groups early in the twentieth century, 276 discrete red-cell antigens have been discovered.*

Maybe D'Adamo should have 276 discrete diets, one each for A+ and A-, B+ and B-, and so on.

On the other hand, as Edward Blonz notes in his review of D'Adamo's Eat Right 4 Your Type:

Blood type is not totally benign. For many years, scientists wondered why type O's were more likely than other blood types to develop stomach ulcers or stomach cancer. In 1993, scientists found that ulcers were caused by helicobacter pylori, a bacterium which had a special affinity for one of the unique type O proteins. A geneticist at Oxford University who checked for other significant associations between the ABO blood types and the incidence of disease, reported that there were only seven; the relationships were often weak; and most, like ulcers, originated somewhere along the digestive tract. If the ABO blood type was that much of a key, as D'Adamo posits, these relationships would be strong and plentiful.*

Dr. Victor Herbert, a hematologist who studied blood and nutrition at New York's Mt. Sinai Medical Center before his death, once said of the theory linking blood type and diet that it is "pure horse manure. It has no relation to reality. The genes for blood type have nothing to do with the genes that handle the food we eat."*

D'Adamo is not alone in this quackery about blood type, however. Obstetrician-Gynecologist Steven M. Weissberg, M.D., and Joseph Christiano, a personal fitness trainer, have co-authored The Answer is in Your Bloodtype: Research Linking Your Blood Type to Life Span, Love and Compatibility, Your Likely Illness Profile, Diet and Exercise for Maximum Life (1996). This pair claims that "You are what you eat, but you should "EAT WHAT YOU ARE.'' This means each of us should eat the optimal diet compatible with our blood type."* They have many anecdotes to support their beliefs.

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."

Not content with limiting his advice to matters of nutrition, D'Adamo claims that blood type affects personality and character. He offers what Dr. Klaper calls "blood type astrology."

In the book [Eat Right for Your Type], 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.*

Many people will no doubt swear by the blood type diet. For example, a vegetarian who eats a lot of wheat may find that D'Adamo's diet recommendations relieved her digestive problems and a host of other ailments. She may attribute her former problems to eating the wrong diet for a type O. However, many people with type O blood are vegetarians or eat wheat without having any digestive problems. On the other hand, some people have gluten intolerance and some have colitis. Their doctors probably advise them not to eat wheat, regardless of blood type.

It could be worse. In Japan, blood type is used like a horoscope (ketsueki-gata). More on this from the BBC.

further reading

reader comments


Bryson, Bill. 2010. At Home: A Short History of Private Life. Doubleday.

Raso, Jack. Mystical Diets : Paranormal, Spiritual, and Occult Nutrition Practices (Consumer Health Library) (Amherst, NY: Prometheus Books, 1993).


Calafell F, Roubinet F, Ramírez-Soriano A, Saitou N, Bertranpetit J, Blancher A. Evolutionary dynamics of the human ABO gene. Hum Genet. 2008 Sep;124(2):123-35.

Saitou N, Yamamoto F. Evolution of primate ABO blood group genes and their homologous genes. Mol Biol Evol. 1997 Apr;14(4):399-411.

Lalueza-Fox C, Gigli E, de la Rasilla M, Fortea J, Rosas A, Bertranpetit J, Krause J. Genetic characterization of the ABO blood group in Neandertals. BMC Evol Biol. 2008 Dec 24;8:342.

Wang J and others. ABO genotype, 'blood-type' diet and cardiometabolic risk factors. PLoS ONE 9(1): e84749, 2014. A study of 1,455 people found no relationship between any health improvements and the subject's ABO blood types. the findings do not support the ‘Blood-Type’ diet hypothesis.


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

Edward Blonz, Ph.D. Book review of Eat Right 4 Your Type (1996) by Peter J. D'Adamo

Does the Eat Right for your Blood Type Diet Really Work? Posts an article by Loren Cordain, promoter of the paleo diet, that cites references (listed above under articles) dating the origins of blood types to much earlier times than D'Adamo.


Link Between Blood Type and Heart Disease Risk Questionable by Walter Jessen "On NPR’s Science Friday last week, host Flora Lichtman talked with Dr. Eric Topol, a cardiologist and director of the Scripps Translational Science Institute in La Jolla, California, who believes that the “dredging of data” — the practice of searching large volumes of data to find any possible relationship — has resulted in a false conclusion....Indeed, the prospective cohort study did not evaluate the biological processes behind blood type and heart disease risk. In fact, the purpose of the two studies evaluated had little to do with blood type. The Nurses’ Health Study, established in 1976, was designed to investigate the potential long term consequences of the use of oral contraceptives. The Health Professionals Follow-up Study, established in 1986, was designed to evaluate a series of hypotheses about men’s health relating nutritional factors to the incidence of serious illnesses, such as cancer, heart disease, and other vascular diseases. "

Blood types indicate greater risk for cancer "....researchers at Dana-Farber Cancer Institute have confirmed a decades-old discovery of a link between blood type and the risk of developing the disease. Blood-type antigens may also affect the level of inflammatory proteins in a person’s blood. Chronic inflammation has been linked to pancreatic cancer risk. Intriguing as these findings are, they don’t necessarily prove a direct link between blood-type antigens and pancreatic cancer development, the authors assert. It is also possible that the ABO gene is merely a marker for other, nearby genes that are more directly involved in cancer development."

What does your blood type say about you? A Japanese minister has resigned, saying that his blood type accounted for his failings.

30,000-Year-Old Flour Finding Suggests Cavemen Craved Carbs  "...scientists using optical and electron microscopy have found 30,000-year-old stones with flour on them at archaeological sites in Italy, Russia and the Czech Republic....These starch grains suggest food processing of plants and possibly flour production was common and widespread across Europe at least 30,000 years ago. These carbs might  have come in especially handy when prey was short, the investigators noted."

So, what happened to these Paleolithic people when they went off the Paleolithic diet?

Dating by blood type in Japan In Japan, there is a widespread belief that blood type determines personality and has implications for life, work, and love. "The received wisdom is that As are dependable and self-sacrificing, but reserved and prone to worry.

Decisive and confident - that is people with type O.

ABs are well balanced, clear-sighted and logical, but also high-maintenance and distant.

The black sheep though seem to be blood group B - flamboyant free-thinkers, but selfish."

Canadian Blood Services uses two pseudosciences, D'Adamo's blood type diet and ketsueki-gata, to entice people to give blood. Skeptic North asks "Do the ends justify the means?" Check you type. It's a good test of the Barnum effect and subjective validation. If you're like me, you have a tendency toward idealism, an aptitude for farming, and a love of vegetables. I consider this spot on because I do like some vegetables.

Last updated 27-Oct-2015

© Copyright 1994-2016 Robert T. Carroll * This page was designed by Cristian Popa.