What Does This Study Mean For You?
Author: Dr. Stephen Chaney
In 1997 Dr. Peter J. D’Adamo wrote a book about the blood type diet called “Eat Right 4 Your Type”. Dr. D’Adamo claims that people with different blood types process food differently, so their blood type determines the type of diet that is healthiest for them. Specifically, he claims that people with:
- Blood group O are descended from hunters and should consume meat-oriented diets.
- Blood group A are descended from farmers and should consume a near vegetarian diet – completely avoiding red meats.
- Blood group B are descended from nomads. They have the most flexible digestive system and can eat the widest variety of foods – even dairy products, which he does not recommend for any of the other blood types.
- Blood group AB is an enigma and are somewhere between blood group A and blood group B.
It’s an interesting concept. Dietary recommendations are made for populations and there is tremendous genetic variation for individuals in every population. Because of this genetic variation, there is no perfect diet for everyone. Every knowledgeable health expert will tell you that.
The question then becomes “How do you know what kind of diet is healthiest for you?”
The blood type diet is a very simple system. Your blood type is easy to determine. Once you know your blood type you know what to eat. There’s no guesswork.
Could it really be so simple? Over 7 million copies of Dr. D’Adamo’s book have been sold. Several celebrities swear by it. Millions of people believe in this concept. So, it is only fitting to ask, “Is it true?”
There is no doubt that blood type is related to some human genetic and physical traits, especially inflammation and immunity. It is also associated with disease risk.
- Type A individuals are more likely to have elevated total and LDL cholesterol are slightly more likely to develop heart disease.
- Type O individuals are slightly more likely to develop type 2 diabetes.
But the important question is whether blood type is related to the health outcomes of different diets – the central thesis of Dr. D’Adamo’s book.
In this article, I discuss a recent study (ND Barnard et al, Journal of the Academy of Nutrition and Dietetics, 121: 1080-1086, 2021) that asks whether the beneficial effects of a vegan diet (the ultimate vegetarian diet) are influenced by blood type. I will also reference previous studies with other diets that asked the same question.
How Was The Study Done?
The investigators enrolled 244 people from the Washington DC area in a 16-week study to measure the metabolic effects of a low-fat vegan diet. Because of the resources necessary to support the study, the subjects were enrolled into 4 replications of the study with 60+ people each between January 2017 and December 2018.
During the second replication of the study (68 participants) blood typing was done to determine whether blood type had any influence on the results. A low-fat vegan diet is the ultimate vegetarian diet. It allows no meat, no dairy, and no animal fats. According to the Blood Type Diet, type A individuals should have much better results on a vegan diet than type O individuals.
The subjects were randomly divided into two groups. One group was assigned to follow a low-fat vegan diet for 16 weeks. The other group was told to follow their regular diet for 16 weeks. Subjects in both groups were advised to follow their usual level of physical activity.
The vegan diet group was instructed to avoid animal products; eat a variety of fruits, vegetables, grains, and legumes; and to limit added oils, nuts, and seeds. They were provided with a B12 supplement to assure none of them developed a B12 deficiency.
The vegan group attended weekly classes that provided dietary guidance and encouraged diet adherence. The classes were conducted by study physicians and registered dietitians. And participants were given handouts at each class to help them follow the diet.
Finally, compliance was assessed by a 3-day diet record interview conducted by trained experts at baseline and week 16.
Is The Blood Type Diet A Myth?
The baseline characteristics of study participants were:
- 80% female
- Average age = 54.
- Average BMI = 32 (obese).
- Average HbA1c = 5.6 (normal blood sugar control).
- Total cholesterol = 195 mg/dL (at the high end of normal).
- LDL cholesterol = 115 mg/dL (at the high end of normal).
And, as expected from previous studies, type A individuals had higher total and LDL cholesterol than other groups. They were borderline high in both categories.
Across all blood type groups, 16 weeks on a low-fat vegan diet significantly decreased:
- Weight (14 pounds).
- BMI (7%).
- Fat mass (11%).
- Belly fat (15%).
- HbA1c (15%).
- Total cholesterol (9%).
- LDL cholesterol (11%).
But the important observations were that:
- When type A individuals were compared with all non-type A individuals there were no significant differences for any of those parameters.
- When type O individuals were compared with all non-type O individuals there were no significant differences for any of those parameters.
- More importantly, no significant differences were observed between type A and type O individuals for any of these parameters.
The authors concluded, “These results indicate that blood type is not associated with the effect of a plant-based diet on body weight, body fat, plasma lipid [cholesterol] concentrations or glycemic [blood sugar] control.”
But the authors also said, “This does not discount the possibility that the effects of diet on health may be dependent on other genetic components.”
What Do Other Studies Show?
Two previous studies have looked at the relationship between blood groups and the effect of diet and health parameters.
The Toronto Nutrigenomics and Health Study (J Wang et al, PLoS One, 9(1):e84740, 2014) was a cross-sectional examination of young adults aged 20-29 to determine whether there was any association of blood type with the optimal diet of those individuals. It found:
- Those with the closest adherence to a blood type A diet had lower BMI, waist circumference, serum cholesterol, serum triglycerids, and blood sugar control) regardless of which blood type they were.
- Those with the closest adherence to a type O diet had lower serum triglycerides regardless of which blood type they were.
The Toronto Health Diet Study ( DJA Jenkins et al, Journal of the American College of Cardiology, 69: 1103-1112, 2017) was a 6-month intervention study that emphasized plant-derived foods but did not exclude meat and dairy. It found:
- Those with best adherence to the prescribed diet had improved levels of several cardiometabolic risk factors (cholesterol, triglycerides, and blood sugar control) regardless of which blood type they were.
In other words, both previous studies showed that primarily plant-based diets significantly reduce multiple risk factors for heart disease and diabetes. They also showed that blood types had no effect on the correlation between diets and health.
The most recent study reinforced these conclusions because it was an intervention study utilized the most rigid form of a plant-based diet. If there were any effect of blood type on the optimal diet, the vegan diet should have produced radically different results in individuals with different blood types.
What Does This Study Mean For You?
First and foremost, the Blood Type Diet is a myth. It has now been proven to be false in multiple clinical studies. If you have a copy of Dr. D’Adamo’s book, my best advice is to throw it in the trash. Normally, I would favor recycling, but I would hate for a book that inaccurate to influence someone else.
And to my friends who have in the past said that they were blood type O and the type O (meat based) blood type diet worked for them, I would refer them to the words of the authors when they said, “This does not discount the possibility that the effects of diet on health may be dependent on other genetic components.”
In other words, there may be some people who do better on a meat-based diet. And that may be based on certain yet-unidentified genes. But it is not based on blood type.
But this study also brings the benefits of primarily plant-based diets into focus. As I have said in previous issues of “Health Tips From the Professor”:
- Short term studies show that whole food, primarily plant-based diets reduce risk factors associated with multiple chronic disease.
- Long term studies show that whole food, primarily plant-based diets reduce the risk of heart disease, diabetes, and some kinds of cancer.
- A well designed and supplemented vegan diet is very healthy. However:
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- Vegan diets are rigid and hard for most Americans to maintain. That’s why only 4% of Americans follow a vegan diet on a regular basis.
- Fortunately, you don’t have to go full vegan to reap the benefits of a plant-based diet. Diets ranging from semi-vegetarian to Mediterranean, DASH, and MIND provide similar benefits. For example, the diet used in the Toronto Health Study referenced above was very similar to the DASH diet.
- Finally, clinical studies are based on averages. The current studies tell us that most Americans benefit from a primarily plant-based diet.
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- However, we cannot currently exclude the possibility that some people might benefit from a primarily meat-based diet. Unfortunately, we have no long-term studies that support that possibility.
The Bottom Line
Dr. Peter J. D’Adamo wrote a book about the blood type diet called “Eat Right 4 Your Type”. Dr. D’Adamo claims that people’s blood type determines the type of diet that is healthiest for them. For example, he claims that blood type A individuals do best with a plant-based diet and blood type O individuals do best with a meat-based diet.
A recent study asked whether the beneficial effects of a vegan diet (the ultimate plant-based diet) are influenced by blood type. It found:
- Individuals put on a vegan diet for 16 weeks had reduced weight, BMI, body fat, belly fat, cholesterol levels, and blood sugar control and those benefits were not affected by blood type.
The authors concluded, “These results indicate that blood type is not associated with the effect of a plant-based diet on body weight, body fat, plasma lipid [cholesterol] concentrations or glycemic [blood sugar] control.” These results are supported by two previous studies that reached the same conclusion using less rigid primarily plant-based diets.
But the authors also said, “This does not discount the possibility that the effects of diet on health may be dependent on other genetic components.”
For more information on this and previous studies and what they mean for you read the article above.
These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.
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My posts and “Health Tips From the Professor” articles carefully avoid claims about any brand of supplement or manufacturer of supplements. However, I am often asked by representatives of supplement companies if they can share them with their customers.
My answer is, “Yes, as long as you share only the article without any additions or alterations. In particular, you should avoid adding any mention of your company or your company’s products. If you were to do that, you could be making what the FTC and FDA consider a “misleading health claim” that could result in legal action against you and the company you represent.
For more detail about FTC regulations for health claims, see this link.
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About The Author
Dr. Chaney has a BS in Chemistry from Duke University and a PhD in Biochemistry from UCLA. He is Professor Emeritus from the University of North Carolina where he taught biochemistry and nutrition to medical and dental students for 40 years. Dr. Chaney won numerous teaching awards at UNC, including the Academy of Educators “Excellence in Teaching Lifetime Achievement Award”.
Dr Chaney also ran an active cancer research program at UNC and published over 100 scientific articles and reviews in peer-reviewed scientific journals. In addition, he authored two chapters on nutrition in one of the leading biochemistry text books for medical students.
Since retiring from the University of North Carolina, he has been writing a weekly health blog called “Health Tips From the Professor”. He has also written two best-selling books, “Slaying the Food Myths” and “Slaying the Supplement Myths”. And most recently he has created an online lifestyle change course, “Create Your Personal Health Zone”. For more information visit https://chaneyhealth.com.
For the past 45 years Dr. Chaney and his wife Suzanne have been helping people improve their health holistically through a combination of good diet, exercise, weight control and appropriate supplementation.
