Blood type diet controversy

There is no reasonable scientific basis for the claim that blood type should determine one’s diet.

Though Peter d’Adamo claims to have collected over 1,000 scientific articles on blood types and their correlations to:

  • Disease
  • Biochemistry
  • Nutrition
  • 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
  • Type O should eliminate grains and do aerobics
  • Types B and AB similar theory

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.

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. From this fact, 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 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.

Group B “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.”

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/nutritionist, 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. 

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.


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