I get a lot of emails about the “Eat Right For Your Type” diet, also known as the blood type diet, which asserts that specific optimal diets exist for each blood type. In this post, I’ll take a look at whether there’s anything to this idea, and whether you should change the way you’re eating based on whether you’re Type O, A, B or AB.

The proposed diets all tend to be pretty decent, whole foods-based ways of eating, and they’re all better than the standard American diet of industrial processed junk, but differences do exist. Here’s the basic breakdown of all four blood type diets:

Type O (PDF): The “original” blood type and the oldest one, proponents claim it evolved among hunter-gatherers in response to their (Primal) diet of animals and plants. People with this blood type do best on meat, fish, and certain fruits and vegetables while limiting starches and omitting grains (especially wheat), beans, legumes, and dairy. It’s pretty much a strict paleo approach.

Type A (PDF): The agricultural blood type, proponents claim it arose after the advent of agriculture. People with this blood type do best on vegetables, fruits, grains, beans, legumes, and limited fish. They should avoid meat, wheat, and dairy. It’s basically a vegetarian diet.

Type B (PDF): The “nomad” type, proponents claim it arose amongst pastoralists raising animals for meat and milk. People with this blood type do best with lamb, mutton, rabbit, and most other meats (except for chicken and pork), dairy, beans, and vegetables. They should avoid wheat, olives, tomatoes, and corn.

Type AB (PDF): The “generalist” blood type. People with this blood type can eat many meats, some seafood, dairy, beans, grains, and fruit, but they should limit kidney beans, lima beans, seeds, corn, beef, chicken, and buckwheat.

I see a few things wrong with their reasoning:

First, they’ve got the anthropology all mixed up. Type O blood isn’t the oldest blood type, nor was it formed by human dietary patterns. The most recent research has found that Types A, B, and O arose almost 20 million years ago in a far-off ancestor common to humans and other primates – long before humans hunted, gathered, farmed, domesticated animals, or even existed. In fact, if anything, it’s type A blood that’s the oldest.

Second, if type A blood arose in response to agriculture, why would the Australian aboriginal diet of meat, marrow, and foraged plant foods, or the Sami diet of reindeer blood, meat, and milk and fatty fish both give rise to a preponderance of type A blood carriers? Type A is supposed to be founded on agriculture – grains, beans, with very little animal products. If a high-animal foods diet selects against type A blood, why does it flourish in these populations?

Third, the justification given for eliminating certain foods from these diets is that the lectins found in them trigger agglutination (clumping) of the red blood cells when consumed by someone with the wrong blood type. So, lectins found in olives are supposed to cause agglutination in Type As, lectins found in grains are supposed to cause agglutination in Type Os, and so on. Proponents claim that specific lectins are selective in their tendency to agglutinate – they interact differently with the various blood types. This supposed selective agglutination is the proximate arbiter of whether a food belongs in a particular blood type’s ideal diet or not, but it doesn’t even exist. The actual research suggests that lectin agglutination is non-selective with regard to blood type. If a particular lectin agglutinates, it generally agglutinates across all blood types. If a lectin is harmful to one blood type, it’s harmful to all.

That said, the blood type diet folks do highlight an interesting observation: the individual blood types are often associated with different rates of certain diseases.

Type Os have a curious relationship to certain infectious diseases. While those with type O blood are more resistant to contracting cholera infections, if they actually get infected, they’re more likely to have an extremely severe reaction. It protects you until you get cholera, after which it leaves you extremely vulnerable. The extreme virulence of cholera to this blood type may even explain the relative paucity of type Os in areas where cholera is common.

Type Os also are far more susceptible to ulcer, now known to be caused by infections from H. pylori bacteria. This is likely explained by the greater preponderance of “H. pylori receptors” in the guts of type O individuals.

Against other diseases, however, type O seems to be somewhat protective:

When compared to other blood types, type O is associated with lower rates of heart disease. The studies (comprising roughly 90,000 people) determined that 6.27% of the cardiovascular disease cases could be attributed to having a non-type O blood type.

Upon reviewing twelve separate studies, researchers determined that type O blood confers protection against pancreatic cancer. Type B was most strongly associated with pancreatic cancer, followed by types AB and A, respectively. Despite the results, “the mechanism by which these SNPs influence risk is unknown.” It could be that “these SNPs may act as markers of allelic variants in nearby genes, and the ABO antigens may not be directly involved in” the development of pancreatic cancer at all. Then, once a person has pancreatic cancer, type O confers a significant survival benefit over the other blood types. This may be explained by the observation in animal studies that the immune systems of types A and B seem to have a harder time at “noticing” and “destroying” cancer cells.

Type Os are also less likely to get gastric cancer, despite their increased susceptibility to H. pylori infections (usually a risk factor for gastric cancer).

These connections are worth looking into and deserve further study, certainly, but they have nothing to say about what diets work best with each blood type.

Obviously, I agree that certain kinds of dietary lectins are problematic, especially if they make it past the gut and into the blood stream. They’re a big reason why I avoid most grains, beans, and legumes – not only do they contain large numbers of lectins, but the lectins they have tend to be particularly proficient at disrupting and navigating the gut barrier. And yes, some people seem more sensitive to dietary lectins than others, but I see no evidence that a person’s lectin sensitivity – and thus ideal dietary composition – is determined by their blood type. It’s an attractive idea, the notion that we can determine someone’s optimal diet and offer them perfect health and protection from disease simply by checking their blood type. It’s just not a realistic one, according to the available evidence.

In the end – and this might be the most important part of this whole thing – the blood type diet “works” because it eliminates processed food regardless of blood type, removes wheat from the diets of people with blood types A, B, and O (which takes care of the vast majority of the population of the world), and recommends that most people (type O is the most common blood type) eat a diet based on meat and plants with little to no grains, beans, sugar,and legumes. I’m honestly not all surprised that so many people get great results.

What about you? Have you tried the blood type diet? Do you know anyone who’s tried it and had success – or failure? If so, what type were they?

Thanks for reading, folks!

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