Eat Right 4 Your Type: The Individualized Blood Type Diet Solution

Overall score

Scientific accuracy

Reference accuracy

Healthfulness

How hard would it be to apply the book's advice? Fairly difficult

Book published in 2016

Published by Penguin Random House, LLC

First revised and updated edition Edition, Hardcover

Review posted August 7, 2020

Primary reviewer: Mario Kratz

Peer reviewer: Seth Yoder

Table of contents

1. Introduction
2. Scientific accuracy
3. Reference accuracy
4. Healthfulness
5. Most unusual claim
6. Other
7. Conclusion
8. Updates

Claim 1

The risk of developing specific diseases depends on an individual’s blood type.

Supporting quote(s) and page number(s)

Page XIV: “In the last twenty years, the scientific community has started to catch up to the fact that our blood types are critical predictive markers for disease. New studies appear every year linking blood type to yet another medical condition.”

More quotes linking blood types to specific health conditions are provided under Criterion 1.1. below.

Criterion 1.1. How well is the claim supported by current evidence?

2 out of 4

A major claim underlying the rationale behind the blood type diet is that the different ABO blood types (A, B, AB, O) are each associated with different risks of diseases.

To address this claim, we investigated whether there is scientific support for 10 claims linking specific blood types to an increased risk of specific diseases. These claims were picked randomly prior to looking into any of the claims made in the book.

Overall, this claim received a score of 2, indicating that overall the claim is weakly supported by current evidence. While some of the claims linking the ABO blood type to higher risks of specific diseases are modestly or strongly supported by current evidence, we were unable to find any support for other claims.

#1: Type O is more likely to suffer from asthma.

“Type O’s win the allergy sweepstakes hands down. They are more likely to suffer from asthma” (page 274).

A review paper published in 2020 that summarized data from 8 studies investigating the relationship between ABO blood type and risk of asthma found that “blood group O is prominent in patients with […] asthma”. That association was not seen in all studies, was weak in most, and in some studies, other blood types were found to have a higher risk than Type O. Thus, while overall the claim is moderately supported by current evidence, the author’s claims are slightly overstated (“Type O’s win the allergy sweepstakes hands down”) relative to the totality of the evidence. Score: 3.

#2: Type A and Type AB have lower levels of intrinsic factor than the other blood types.

“Type A and Type AB have lower levels of intrinsic factor than the other blood types” (page 280).

Intrinsic factor is produced by the stomach and plays a key role in the absorption of vitamin B12. Thus, the claim suggests lower vitamin B12 absorption in blood types A and AB. We could not find any publications supporting this claim. Score: 1.

#3: Type O is more susceptible to bleeding disorders and excessive blood loss.

“Type O faces the biggest problems when it comes to blood clotting. Most often, Type O lacks insufficient quantities of the various blood clotting factors. This can have severe consequences, especially during surgery or in situations where there is blood loss” (page 281).

We did indeed find several publications reporting greater risk of heavy bleeding, for example during menstruation or childbirth, among individuals with blood type O. However, the association is not consistently seen, suggesting selective consideration of the literature. Score: 3.

#4: Type A and Type AB have ‘thicker’ blood that is more susceptible to clotting.

“In studies, Type A and Type AB individuals tend to predominate with clotting disorders, and their thicker blood can work to their disadvantage in other ways” (page 281).

We found several publications reporting an increased risk of thrombosis in individuals with non-O blood types, and this association seems to be seen fairly consistently. This includes individuals with Type B compared to Type O, but in general this claim seems to be well supported by ample evidence. Score: 4.

#5: Type A and Type AB have a higher risk of cardiovascular disease.

“Type A and Type AB have a higher risk for cardiovascular disease” (page 282).

Cardiovascular disease is a term that includes coronary artery disease, such as myocardial infarction (heart attack), but also strokes and peripheral artery disease. According to a 2016 meta-analysis of 17 observational studies, blood type A does indeed have an increased risk of coronary artery disease (by 14%) compared to non-type A. Also, blood type O has an 15% reduced risk of coronary artery disease compared to non-O blood types (which include types A and AB). Blood type AB does not differ in its risk of coronary artery disease compared to non-AB blood types. Thus, with regard to coronary artery disease, the claim is partly supported by current evidence.

Fewer studies have investigated the relationship between ABO blood types and risks of strokes or peripheral artery disease. A 2014 case-cohort study found that blood type AB is associated with an increased risk of stroke compared with non-AB blood types. Blood type A was also found to be associated with greater risk of peripheral artery disease in the Multi-Ethnic Study of Atherosclerosis.

Taken together, there is good and consistent evidence that blood type A is associated with an increased risk of coronary artery disease and peripheral artery disease, and blood type AB with an increased risk of stroke. Score: 4.

#6: Type A and Type AB children are more susceptible to conjunctivitis.

“Type A and Type AB children are more susceptible to conjunctivitis” (page 287).

We were unable to find any publications investigating the relationship between ABO blood types and conjunctivitis. Score: 1.

#7: Blood Type A and Type B individuals are more prone to type 1 diabetes.

“Blood Type A and Type B individuals are more prone to type 1 diabetes” (page 294).

We were unable to identify any publications investigating the relationship between ABO blood types and type 1 diabetes. Score: 1.

#8: Stomach ulcers are more common in Type O and Type B.

“Ulcers are produced by hyperacidity, more common for Type O and Type B” (page 300).

There is some older evidence that consistently linked blood type O with a higher risk of peptic (stomach) ulcers. Even though these studies were mostly small and in some cases not on par with modern epidemiologic methods, the available literature fairly consistently supports the notion that blood type O is associated with peptic ulcers (i.e., ulcers of the stomach). However, we did not find similar evidence for blood type B. Score: 3.

#9: Gastritis is more common in Type A and Type AB.

“Gastritis is caused by very low stomach acid content, more common for Type A and Type AB” (page 300).

We identified a 2003 observational study that investigated the relationship between the ABO blood types and atrophic gastritis. These investigators had access to blood type data and data on gastritis from two different groups of participants. In one of these, they found a higher risk of atrophic gastritis among individuals with blood types A or B compared to O, with no significantly elevated risk in individuals with blood type AB compared to O. However, the ABO blood types were not associated with atrophic gastritis in the second group, even though the groups were fairly similar to one another. These discrepant findings make this study a bit inconclusive. We also identified a 2011 study that reported lower risk of atrophic gastritis among individuals with blood type B compared to blood type A. None of the studies we found reported an increased risk of gastritis abong blood type AB individuals. Score: 2.

#10: Viral infections are more frequent in Type O.

“It has been observed that viral infections in general seem to be more frequent in Type Os because they do not possess any antigens” (page 302).

Blood type O is associated with an increased and blood type B is associated with a decreased risk of hepatitis B infection compared to other blood types, consistent with the claim. A 2015 study found no association between ABO blood types and infection with the virus that causes Chikungunya disease. ABO blood type was also not associated with clinically critical influenza infection caused by the H1N1 subtype. Another study looking at epidemic influenza caused by the H3N2 subtype in Western Australia found an increased risk of infection among blood type B individuals compared to non-blood type B, a finding directly opposite of what is claimed in the book. Another paper published almost 50 years ago investigated the relationship between ABO blood groups and numerous viral infections, concluding that they failed to “reveal any consistent statistical relation between ABO blood groups and viral infections”. A large observational study published in 1962 found increased risk of infection with influenza A2 virus among blood type O compared to non-O, but the opposite trend for adenovirus infections, and no associations between ABO blood groups and infections with influenza A1, influenza B, and Coxsackie A21 viruses. Thus, taken together, the existing literature does not provide support for the claim that viral infections are more frequent in individuals with blood type O compared to non-O. Score: 1.

Of particular relevance in the year 2020, when this review is published, is the finding that people with blood type A had a significantly higher risk of infection with the novel coronavirus (SARS-CoV-2), whereas blood group O had a significantly lower risk of SARS-CoV-2 infection. This finding is the opposite of what is claimed, but was not considered in scoring the claim because it was published after the book was published.

Criterion 1.2. Are the references cited in the book to support the claim convincing?

1 out of 4

The author does not provide any references for any of the specific claims.

Criterion 1.3. How well does the strength of the claim line up with the strength of the evidence?

2 out of 4

The claim received a score of 2, indicating that it is moderately overstated. As outlined above, there is some evidence that ABO blood types are associated with a higher risk of certain diseases. However, even in those cases where evidence exists, the book often oversimplifies or overstates the evidence. With regard to some other diseases or conditions that the author claims are associated with ABO blood types, we were unable to find any support for the author’s claim in the scientific literature (e.g., type 1 diabetes, conjunctivitis).

Overall (average) score for claim 1

1.7 out of 4

Claim 2

The ABO blood type determines whether a food is healthy, neutral, or unhealthy for an individual.

Supporting quote(s) and page number(s)

“Your blood type is the key that unlocks the door to the mysteries of health, disease, longevity, physical vitality, and emotional strength. Your blood type determines your susceptibility to illness, which foods you should eat, and how you should exercise” (page 1).

Criterion 1.1. How well is the claim supported by current evidence?

1 out of 4

Based on our extensive literature search, no scientific studies have provided evidence that adherence to the specific recommended diets for each ABO blood type leads to better health outcomes. A 2013 review article on the topic concluded that ‘no evidence currently exists to validate the purported health benefits of blood type diets’.

In 2014 and 2018, a Canadian research group published papers in which they aimed to put the blood type diets to the test. They calculated adherence scores for each of the four blood type diets among participants in two different studies. While they found modest improvements in biomarkers of cardiometabolic disease in participants with higher scores of some of the blood type diets, these benefits did not differ based on the participant’s blood type. These two publications have often been cited in the media as ‘debunking’ the blood type diets. This assessment is debatable. Even though the authors are to be commended for attempting to put the blood type diets to the test, the methods used in these studies do not provide much insight into whether the idea behind the blood type diets is valid. For one, the authors utilized a fairly crude instrument, the food frequency questionnaire (FFQ), to assess dietary intakes in both studies. These FFQs measure intake in broad categories, such as ‘beans’ or ‘grains’, which does not provide enough detail to adequately gauge adherence to any of the blood type diets. For example, black-eyed peas are considered ‘highly beneficial’ for Type O individuals, while kidney beans are to be avoided. It’s the exact other way around for blood type B. A FFQ will provide information on total bean intake, but not nearly enough detail on what types of beans were consumed. Thus, we question that a score based on a FFQ could adequately reflect adherence to a blood type diet. A second problem with these studies is that scoring participants in an observational analysis is likely not appropriate. If the book’s hypothesis were correct that consumption of foods in the ‘avoid’ category would trigger disease processes, for example through specific interactions of a dietary lectin with a blood type antigen, then it would not matter whether someone was 40% or 60% or 80% adherent: in all cases, there would still be substantial exposure to the allegedly disease-causing lectin.

Thus, while we rate the claim with a score of 1, indicating that currently no scientific evidence exists to support this claim, it is important to emphasize that there also is no evidence to prove that the blood type diets do not work. As outlined elsewhere in this review, there is some indirect support for the idea that the disease risks of individuals with different ABO blood types differ. It is also not out of the question that people with different blood types respond differently to foods. Providing conclusive evidence would be very difficult and very costly, because we would need to conduct a study of individuals randomized to ‘their’ specific blood type diet or any of the other three, with very long-term follow up to assess impacts on chronic disease. At this point, the absence of evidence should not be seen as evidence that the claim is incorrect. However, it is important to emphasize that the claim is currently not supported by any, even weak, scientific evidence.

Criterion 1.2. Are the references cited in the book to support the claim convincing?

1 out of 4

The author does not cite any references in support of specific claims.

Criterion 1.3. How well does the strength of the claim line up with the strength of the evidence?

0 out of 4

We scored this claim as 0, indicating that the claim is greatly overstated. As we discussed above, there is no evidence in general that a specific blood type diet has health benefits specific to that particular ABO blood type. There is also no evidence for most of the very strong claims the author makes throughout the book about very specific positive or negative health effects of certain foods for the specific blood types. Examples include, on page 138: “Soybeans contain a lectin called genistein that may protect Type A against certain cancers”, or on page 207/208: “The edible snail, Helix aspersa/pomatia (escargot), contains a powerful lectin that may help prevent some cancers that Type AB individuals appear more prone to developing.”

Overall (average) score for claim 2

0.7 out of 4

Claim 3

Lectins in foods interact with specific blood type antigens, which partly explains the differential health effects of foods on individuals with different blood types.

Supporting quote(s) and page number(s)

“Simply put, when you eat a food containing protein lectins that are incompatible with your blood type antigen, the lectins can attach to the walls of the digestive tract, initiate inflammation, and even penetrate the gut lining and escape into the circulation” (page 35).

“The key is to avoid the lectins that agglutinate your particular cells – determined by blood type” (page 36).

“In general, beans […] contain lectins that are harmful to Type O” (page 100).

“Be aware, however, that not all beans and legumes are good for you. Some, like kidney, lima, navy, and garbanzo, contain a lectin that can cause a decrease in insulin production, which is often a factor in both obesity and diabetes” (page 139, under ‘The Type A Diet’).

“In my experience, one of the most difficult adjustments Type B must make is giving up chicken. Chicken contains a Blood Type B agglutinating lectin in it’s muscle tissue” (page 171).

“Although they can be a good supplementary protein source, seeds are a common source of food lectins, and your double AB antigens afford them ample opportunities for mischief” (page 212, under ‘Blood Type AB Diet’).

Criterion 1.1. How well is the claim supported by current evidence?

2 out of 4

We found a very rich literature that clearly demonstrates that (a) lectins can bind ABO blood group antigens, and (b) that binding is usually specific for a particular lectin-blood type-antigen pair. These two observations together support the general statement that lectins selectively bind specific blood group antigens. Most of the research that identified blood type antigen-specific lectins did not test dietary lectins, however, but instead was conducted using human lectins, microbial lectins, or lectins from the seeds of non-edible flowers.

We did identify, however, some publications showing blood type antigen-specific binding of some dietary lectins. These included papers showing that lima bean lectin is specific for the type A antigen, that peanut lectin binds different blood type antigens differently, and that the lectin from a crab is specific for type B antigen. Another paper from 1962 that unfortunately lacked a lot of detail reported that numerous legume lectins including those from peas, fava beans, and runner beans were able to bind roughly equally well to all ABO blood type antigens. Some older, very interesting papers discuss the blood type-specificity of certain lectins in detail.

Unfortunately, the author does not cite any references, and also does not disclose by which methods he obtained the very detailed information on which dietary lectins bind to which blood type antigen. It is therefore possible that some relevant literature was missed during the review process. Still, while there is some evidence that some lectins bind ABO blood type antigens exclusively or preferentially, most of the very specific recommendations made in the book are not based on solid – or any – scientific evidence.

Moreover, no evidence was observed that binding of lectins to cell surfaces increases the risk of disease. As we discussed in more detail in our review of ‘The Plant Paradox’, lectins are a potentially very interesting component of the human diet in that they largely resist digestion, are able to enter the human bloodstream, can attach to the surface of cells, and can trigger an immune response. At the same time, most of the experiments on the health effects of lectins have been conducted in animals, using very high concentrations of isolated lectins. Human intake is much lower than in these animal experiments, largely because preparation and processing remove or destroy most lectins, a fact the book does not provide much detail on. It therefore remains unclear whether dietary lectins consumed in much lower doses from properly prepared foods are involved in the development of human disease, or whether avoidance of specific dietary lectins can prevent or reverse disease.

We therefore gave this claim a score of 2, indicating that it is weakly supported by current evidence. This really applies only to the binding of specific blood type antigens, for which there is evidence for some dietary lectins. At this time, no direct evidence exists that this binding is problematic for health in general or involved in the development of specific diseases in particular.

Criterion 1.2. Are the references cited in the book to support the claim convincing?

1 out of 4

The author does not provide any references for any of the specific claims.

Criterion 1.3. How well does the strength of the claim line up with the strength of the evidence?

1 out of 4

The claim received a score of 1, indicating that the author substantially overstated the strength of the evidence, in two regards. First, solid scientific data on the blood type-antigen-specificity of dietary lectins is very sparse, and nowhere near as detailed as claimed in the book. Second, we are not aware of any direct scientific evidence that links specific dietary lectins to the development of disease.

Overall (average) score for claim 3

1.3 out of 4

Overall (average) score for scientific accuracy

1.2 out of 4

Summary of the health-related intervention promoted in the book

Eat Right 4 Your Type recommends that individuals follow a specific diet based on their ABO blood type. For each diet, the author presents detailed tables with foods labeled as “highly beneficial”, “neutral”, or “avoid” for that specific blood type. As outlined elsewhere in this review, the categorization of foods into these three groups is based on the idea that structures on the surface of cells in the body (so-called blood type antigens) interact with our food in specific ways, making each food either health-promoting, neutral, or health-damaging for an individual based on their specific blood type. For maximum health benefit, the author recommends a “10-day blood type diet challenge.” For the first 5 days, only foods from the ‘highly beneficial’ category are allowed in order to eliminate exposure to damaging dietary lectins. This phase is therefore called “lectin detox.” For the second 5-day period, some neutral foods can be added, but “avoid” foods remain entirely off limits. Outside of this very strict 10-day challenge, a more modest version of the blood type diet can be adopted, with occasional consumption of some “avoid” foods in small amounts if tolerated.

Condition targeted by the book, if applicable

N/A (the book does not target one or several specific conditions)

Apparent target audience of the book

The book is written for a general audience.

Criterion 3.1. Is the intervention likely to improve the target condition?

N/A

The book does not target one or several specific conditions.

Criterion 3.2. Is the intervention likely to improve general health in the target audience?

3 out of 4

The blood type diets received a score of 3, indicating that they are likely to moderately improve general health, if strictly applied as recommended by the author. This is mostly because the foods that are specifically recommended and listed under ‘highly beneficial’ include mostly whole, unprocessed, nutritious foods for all four blood type diets. This will lead to high or very high intakes of most micronutrients as well as other health-promoting dietary components, such as fiber and phytochemicals. At the same time, highly processed foods will mostly not be consumed, because they often contain a large number of ingredients, at least one of which will be on the ‘avoid’ list. The recommended diets were not scored more highly because sources of empty calories such as white wheat flour or added sugar are on the neutral list for most of the diets. Thus, individuals following these diets could be compliant and potentially still eat large quantities of baked goods such as cookies, cakes, or pies. As outlined elsewhere in this review, whether the recommendations to consume the specific blood type diet provide health benefits over general dietary advice to follow a healthy dietary pattern remains unclear.

Criterion 3.3. Does the diet portion of the intervention promote an adequate nutrient intake for general health in the target audience?

2 out of 4

The blood type diets received a score of 2, indicating that these diets are likely nutritionally adequate. As outlined above, strictly following the recommendations for any of the four blood type diets will substantially increase nutrient density and with that the intake of most vitamins, minerals, and trace elements in most people, particularly those who switch over from an average American diet. At the same time, white wheat flour and added sugar are on the ‘neutral’ lists for most diets, which would allow individuals to consume potentially large amounts of empty calories. This could lead to a substantial reduction in the intake of micronutrients and other beneficial dietary components such as fiber or phytochemicals. Another potential concern is that the diets may be unnecessarily restrictive. For example, the recommendation that Type A individuals largely avoid meats and dairy foods could lead to borderline low intake of some essential nutrients such as iron, vitamins B2 and B12, and calcium. To be fair, this is partly balanced by the specific supplement recommendations made, but it still indicates that all four diets are not providing all micronutrients with a wide margin of safety.

Overall (average) score for healthfulness

2.5 out of 4