Eat Right for Your Type: Debunked Again?

I have posted a number of times about the blood type diet, as described in the book Eat Right For Your (Blood) Type (1996), by Peter D’Adamo (see posts).

I lived in Atlanta during the late 1990s and it was quite popular there at the time. And why not? Who wouldn’t want to eat right for their blood type?!

While the diet and book are a stroke of marketing genius, in my humble opinion, it is also a very far-fetched piece of science. I’m talking way out there. La la land.

I should probably mention that this humble opinion is shared by every medical doctor, nutrition research scientist, and dietitian I’ve ever heard on the subject.

Most unfortunately, the blood type diet has never been tested with an actual clinical trial. Rather RDs, MDs, PhDs, and even WMDs, dismiss it by saying that there is simply no evidence to support it. And while I’m terribly sympathetic to the idea that there is no evidence to support it, I don’t think this is satisfying to a layperson who reads the book. When the subject comes up, I can almost see them thinking to themselves, “You silly dietitians are just brainwashed by the grain and dairy lobbies,” or whatever they think might be biasing that particular dietitian (such as the desire to promote veganism among people with all blood types).

We now have at least a cross-sectional study that provides more evidence about the (lack of) effectiveness of eating right for your blood type (1).

The participants were 993 women and 462 men, aged 20 to 29 years old, taking part in the Toronto Nutrigenomics and Health study.

Based on the food items listed in Eat Right for Your Type, subjects received a positive point for consuming a serving of a recommended food item for one’s blood type and a negative point for eating a food to avoid. The foods that were not listed either to consume or avoid were ignored.

Here is an idea of what the diets are like:

A – almost vegan (no meat, little dairy)
B – semi-vegetarian (low grains, more dairy)
AB – very similar to B with a little less fruits and vegetables and a little more meat
O – paleo (high-meat, high-vegetables, no grains and little dairy)

The data was analyzed in two different ways.

In the first, the entire population was separated into thirds according to their scores for each diet and regardless of their blood type. To make a long story short, the type A and type AB diets fared the best in terms of disease risk factors (see the abstract linked below for the details).

The second set of analyses had four separate sub-analyses in which everyone was divided according to how close they ate the particular blood type diet being examined. Then the people with that blood type were compared to the rest of the population. According to the authors, “no significant interaction effects were observed between diet adherence and blood group for most of the risk factors, suggesting that effects of following ‘Blood-Type’ diets is independent of an individual’s blood group.”

Note that they said no significant interaction was found for most of the risk factors. Given the number of data points they compared (hundreds), it is not surprising that they found some statistically significant, but still rather weak associations, and, in my opinion, the associations they found were inconsistent enough to be meaningless.

With this study, I think we finally have something that moves beyond “no evidence to support” to “evidence to disprove.” However, it still isn’t going to be very persuasive to a believer, especially given how hard it is to explain.

Clinical trials are expensive and since no researcher actually believes there’s anything behind the blood type diet, it’s no wonder that more money hasn’t been forked out to test it.

The diet seems to have gone out of fashion, but if it experiences a resurgence, it might be time to bite the bullet and spend the money on a clinical trial that, with little doubt, would finally allow us to show people that there is no need to eat according to your blood type.


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1. Wang J, García-Bailo B, Nielsen DE, El-Sohemy A. ABO Genotype, ‘Blood-Type’ Diet and Cardiometabolic Risk Factors. PLoS One. January 15, 2014.
DOI: 10.1371/journal.pone.0084749 | link

14 Responses to “Eat Right for Your Type: Debunked Again?”

  1. Bertrand Russell Says:

    Jack, didn’t you once do a survey of long-time healthy vegans, and find that the distribution of blood type in this survey mirrored the population as a whole? (E.g., there were just as many “Type O” healthy vegans as you would expect from the general population, rather than there being none if “Type Os” really needed to eat meat.)

  2. Jack Norris RD Says:


    I did. I think it was about 70 people. I also asked them if they had felt their health improved, stayed the same, or decreased after going veg and found no differences in experience between blood types. It was an informal survey though and I lost the data many years ago when changing computers.

  3. MDR Says:

    I will say I am a type O negative, and for years I have noticed that when I drink beer I have severe bloating, also that major inflamation from pastas, and grains, I tried the suggested type o diet, I lost 15lbs, had more energy, clearer thinking and overall much better health. not saying that I am the absolute proof of the legitamacy of the diet. But it did really work for me.

  4. Jack Norris RD Says:


    I don’t want to censor comments, so I put yours through, but it sounds like you might be trolling the web for anti-blood type diet articles.

    One person having a good experience changing their diet from whatever it was to the diet recommended by D’Adamo is not evidence that the theory that the diet is based on is true. Maybe you do better not drinking beer or eating certain grains – this probably has nothing to do with your blood type. Giving up beer could very well lead to losing 15 lbs, among other things.

  5. Jack Norris RD Says:

    I should have added, I’m type O and I eat grains and gluten like they’re going out of style and I’ve been pretty much thriving on a vegan diet for 25 years now.

  6. Rhys Says:

    I think one reason this diet might appeal to some people is that it’s a new way to attach meaning to a trivial fact about ourselves. (Or “seemingly trivial fact” for people who believe in it.) Of course blood type isn’t trivial as far as blood transfusions and other issues relating to blood type incompatibilities, but believing in the blood type diet adds a new layer of significance to this fact about ourselves that we’re born with and is out of our control. It’s a bit like astrology, which people use to find meaning through the exact moment of their birth. It’s maybe interesting to think that we’re all unique and yet each contain a map giving us clear directions in how to live: if only we know how to look for this map.

    Plus there’s the fact that nutrition is mysterious to most people, and some people do seem to do better on different sorts of diets, so it’s kind of comforting to think that we can divine the answers to nutritional mysteries through a simple blood test. “Hey, I fit this one category that I never thought about before, and now I know exactly what to do if I’m in this category.”

    That there is no evidence supporting the blood type diet definitely poses a problem for its adherents, but maybe they’ll be able to derive similar sorts of meanings — and maybe some actually useful insights — through DNA testing.

  7. dimqua Says:

    Stupid question, but … what does WMD mean?

  8. Jack Norris RD Says:


    It was a joke. It stands for Weapons of Mass Destruction. I was just trying to find another acronym that ended in “D”.

  9. BillD Says:

    I am (was) about a 98%+ ethical vegan. (for about 30 years) My acupuncturist believes in the “Blood Type Diet”, and wants me to start eating animal flesh. He thinks I am “low on (“good”) protein consumption”. I was feeling pretty bad (basically all of the expensive “real doctor” tests came back negative, as usual — I basically felt ‘well/better’ (pre-bad-level) after his first treatment, with little additional betterment sense), so I agreed to start eating eggs. He wanted two a day, which I did for a few weeks, and now I’m eating one a day. I am also eating half of the suggested intake of a hemp-based protein powder (with other plant-based proteins). I don’t think protein is my problem. We looked into this diet years ago and discovered it is most probably bogus. Every vegetarian and vegan I know (some as long or longer than I have been) is in really good health except me.

  10. Jack Norris RD Says:


    Did eating eggs help? In what way have you been feeling bad?

  11. BillD Says:

    Afaict, “eating more protein” hasn’t helped. (after a couple of months) It’s difficult to say how I’ve been feeling bad. The best way I can describe it is how you feel when you have a cold or the flu, and without the sneezing, coughing, congestion, etc., how you just don’t feel well. That’s more or less how I feel all the time. (Doctors love it when that’s how you describe it [/sarcasm]) I have “good days” and worse days. (weeks/months — seemingly random) And I usually have very low energy. My primary problem is that I have what I call “Stress Sickness”, which, of course, “there is no such thing”. But years of EXTREME stress as a computer programmer, with being “burned out” again and again in job after job, has taken an increasing negative toll on my health, and effectively made me (literally) “allergic to stress” (which, of course, “there is no such thing”), and my health has now deteriorated over time. (“stress is a killer”, or will send you in that general direction) I also think my adrenal glands have basically stopped functioning, which the Physician’s Asst. ignored and shrugged off. But I think, if I drink a Red Bull energy drink and it has no effect on me, like I might as well be drinking water, that “means something”. So I guess I have at least “Chronic Fatigue Syndrome”, among some other ancillary issues. All the PA could tell from all the tests was that my thyroid was a little on the low side, low enough that I could take medication for it, or not, although taking it might help some. So I am taking a more natural version that my acupuncturist suggested and some high potency iodine, which has helped some. Pretty much everything I’ve ever tried, like “eating better”, taking vitamins, supplements, etc., has never done much for me. But, like I said, I have to be feeling pretty bad to go see a “real doctor”, and after the first treatment by the acupuncturist, I felt quite a bit better, and marginally more so after a few weeks of treatment, which is what he generally does for me. (I should have just skipped the “real doctor” and the expensive tests, which I can’t afford (on Medicare)) Unfortunately, I had to go on disability several years ago, and, like everyone I’ve ever known or heard about being on disability, my health has slowly deteriorated over time. I’ve never heard of anyone getting better, much less “well”. So I’m just existing these days, as best as I can. But it doesn’t bode well. “Poor me”. But I don’t complain, because I could be a lot worse off, as I was right before I went on disability, and, of course, there are MANY, MANY more people in the world who have MUCH worse lot in life than I do. btw — for those who think “eating meat” is a good thing, and think it makes them feel better, gives them more energy, etc., I always compared it to putting Premium Unleaded gasoline in an old-style “Regular” fuel car — it may seem to run well for awhile, with more power, etc., but after awhile it will wreak havoc and burn up the engine.

  12. Jack Norris RD Says:


    It sounds like you have a problem that is not easy to diagnose. Have you had your vitamin D levels tested? Your symptoms make me think that if your problem is nutrition-related, that might be a potential cause. Have you been tested for lyme disease? How do you get vitamin B12 (how much and how often)?

  13. BillD Says:

    The PA did want to do another blood test to check for vitamin D levels, I can’t remember why, but that’s just another expensive test I can’t afford. I guess I’ll do it anyway since you brought it up. My B12 levels were fine — she no doubt checked them because I told her I am a vegan. (afaik, that’s another urban myth, that veg(itari)ans have problems with B12 / vitamin B’s) And I was bitten by a tick about 30 years ago. But I thought they couldn’t test for lyme disease after so long. And/or there wasn’t really anything that could be done about it because you have to treat it within the first 6 months or something. Thanks.

  14. Jack Norris RD Says:


    You could also just take vitamin D and see if it helps. I’d recommend 4,000 IU per day for two weeks.

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