New Research Shows The Blood-Type Diet May Not Be Good For You

The first time I took this diet seriously was actually less than a year ago, when another health care practitioner recommended it to me.  I had heard about it for years as a good lifestyle changing diet, and thought "why not-I could use a little better structure to my eating habits".  I am type O, so I prepped myself to launch full on into heavy protein eating.  As a former Selectarian (ate fish and sometime meat occasionally), it was fairly hard to stomach the huge amount of protein the O type calls to eat.  I gave up in few weeks thinking this lifestyle change is not for me, I want a big huge salad.  I listened to my body instead of what a book said.  Low and behold, my body was right. 

The blood-type diet — otherwise known as “Eat Right 4 Your Type” — has by now been soundly debunked. Yet, in the late 1990s, it held pride of place as the hottest concept in dieting, embraced by celebrities, self-proclaimed nutrition pros, and teenagers like me who believed they’d discovered the most ancient secret to looking cute in hip-huggers. What fools we’d been to chug SlimFast and count Weight Watchers Points, when all along the answer had been coursing through our very veins. 

In 1996, Peter J. D’Adamo published Eat Right 4 Your Type, the best-selling book that launched the blood-type diet into cultural consciousness.   He was the son of another famous naturopath, James D’Adamo, who first posited the idea that a diet based on blood type might have health benefits. The senior D’Adamo prescribed a low-fat, vegetarian diet to all his patients, noting that some seemed to exhibit improved health, others remained the same, and some got worse. Could blood type be the cause? While his theory was based only on observations within his practice, his son sought to validate them with research. “What I had been taught about blood transfusions and other aspects of blood typing didn’t give me any information that supported my father’s ideas about how people should eat,” said Peter J. D’Adamo in an undated interview. 

While at Bastyr, he began looking at connections between blood types and illnesses,thinking, “‘If my father’s right, the type A’s should have illnesses associated with eating meat, because he said they shouldn’t consume that.’ It was no surprise when I found that a lot of health problems associated with excessive animal protein consumption, like heart disease, cancer, and vascular disorders, were much more common in type A’s.” According to D’Adamo, each blood type has different abilities to process certain foods — as well as the lectins found in many of them. Lectins are a vast group of carbohydrate-binding macromolecules that serve numerous biological functions. D’Adamo’s claims that the different blood groups are unable to properly metabolize certain lectins, and therefore if you eat the wrong food, the lectin “settles” somewhere in your body, causing agglutination (cell clumping). This “dangerous glue” he continues, can cause everything from hormone disruption to liver cirrhosis, or even block blood flow to the kidneys, “to name just a few effects.” 

Today, D’Adamo sells a pill of “blocking sugars” called Deflect, designed to stop this clumping. Indeed, he now has several supplement lines intended to support each blood-specific diet, but back in the ’90s the diet alone was the cure. Based on his and his father’s observations, D’Adamo formulated four separate profiles based on each of the blood types. In summary:

Type O: This, the oldest blood type, is well suited to metabolizing animal protein, fat, and cholesterol, but not grains or dairy. As this blood type is descended from hunters, the fight-or-flight response is strong and can translate to anger issues or manic episodes. Type O's are also vulnerable to destructive habits when bored; they should avoid caffeine and lentils, engage in vigorous exercise, and remember to chew slowly.

Type A: This blood type emerged with the rise of community living, when, thanks to the dwindling supply of game to hunt, human digestion was forced to adapt to carbohydrate consumption. Type A’s, therefore, should eat mostly vegetables and soy proteins, being mindful of their highly sensitive immune systems and increased risk of life-threatening disease (as well as naturally higher stress levels). They should avoid crowds and corn, andpractice tai chi.

Type B: “B is for balance!” While Type A and O are on opposite ends of the spectrum, B falls somewhere in the omnivorous middle. Meat, dairy, grains, legumes, fruit, vegetables — Type B’s really need them all (except chicken). When these are out of balance, the B’s can be prone to stress and illness, but when they are eating for their type, they are more physically and mentally fit than other blood types. D’Adamo notes that B’s may also have a “sixth sense,” as they are intuitors. 

Type AB: The rarest and newest of the blood types is what D’Adamo calls “the chameleon.” It is the only one that emerged not from environmental factors but from intermingling, and is somehow more mystical than the others. Lamb, dairy, tofu, and grains are all good for AB’s, while buckwheat and smoked meats can be problematic. They are charismatic, have low stomach acid, and should practice visualization techniques. 

“It’s just a really cool idea that has no substantive support.” This is the take of Dr. Ruth Kava, PhD, RD, the Senior Nutrition Fellow at the American Council on Science and Health. “There's no consistency, no logical rationale for this diet.” It’s a common-sense conclusion when you look closely at D’Adamo’s plans — both their broad generalizations about billions of people and highly specific instructions about how they should eat (and exercise and manage their mental health). But Dr. Kava isn’t as swayed by that part. The idea that blood types emerged with the milestones of human societal development also seems like logic on the surface. “There's no real scientific connection between [these events],” she adds. “But it does sound very impressive.”

What further complicates the matter is that D’Adamo’s unproven statements about blood types sound similar to facts that do have scientific backing. While there’s no evidence that blood type is so directly linked with evolution, it is likely that certain antigens evolved with humans to protect us from environmental threats (like malaria). It’s also true that there is ahigher incidence of certain illnesses in different blood groups, though the reasons are as yet unclear (and, adds Dr. Kava, “they have nothing to do with diet”). 

Furthermore, it’s likely that many people could stumble into better health while eating on one of these plans, not because they’re “eating right for their type” but because they’re simply eating better than they were before. In fact, one study found that adherence to the O, A, or AB diets (but not B) may be associated with improvements in specific biomarkers of cardiometabolic health. However, they found the same results in all 1,455 study subjects, regardless of blood type. Matching the diet with its corresponding blood group “did not change the effect.” If you go from eating no vegetables to suddenly integrating produce into your diet, “That’s a good switch, but it's got nothing to do with blood type,” says Dr. Kava. 

The fact is, we don’t yet have a clear explanation for why people have different blood types. Scientists have been looking for one ever since Karl Landsteiner discovered and categorized the ABO blood groups in 1909, but so far the only simple answer is that there are no simple answers. Blood is not a single substance, after all. It is cells, plasma, platelets, and proteins; it holds our commonalities as a species but also the specifics of our own genetic line. Even if D’Adamo’s theory that blood types conveniently emerged based solely on food availability had any scientific backing (which it doesn’t), he ignores the massive changes in our dietary patterns since then. He ignores the fact that Type A and Type B parents can produce a Type O child (practically a different species in D’Adamo’s world). He ignores further scientific factors that might complicate his theory — for example, the Hh blood group. Also known as the Bombay Phenotype (it is most concentrated in Indian populations, but also appears in Asia and Europe), it is comparatively quite rare. Yet that’s still millions of people with Hh blood and no diet to eat right for. 

We don’t know everything about blood type, and we don’t like not knowing. We want someone to solve the mystery of our bodies, tell us how to get thin and not get cancer. D’Adamo claims to have the answers for that and more. Your stress, your sadness, your love of pilates — it’s all there in your blood. How easy it would be to just sidestep that vast, discomforting lack of knowledge and choose to believe the truth is in our very veins.  Unfortunately, there is just not sound evidence to support that idea.