In 1997, Peter D’Adamo published the book Eat Right 4 Your Type, a book that argues that in order to eat a healthy diet, different blood types need different diets. For instance, D’Adamo makes the claim that blood group O needs a different diet than blood group A.
The book has seen tremendous commercial success, with there now being over 7 million copies circulating worldwide in over 60 different languages. But is there good evidence that different blood types need different diets? Is there good evidence that blood type diets lead to better health outcomes?
Recently, researchers conducted a systematic review examining the evidence for blood type diets. Their findings were published in the most recent issue of the American Journal of Clinical Nutrition.
The researchers asked the question, in humans grouped according to blood type (population), does adherence to a speciﬁc diet (intervention) improve health and/or decrease risk of disease (outcome) compared with non-adherence to the prescribed diet (comparison)?
They searched the Cochrane, MEDLINE and Embase databases, scanning titles and abstracts for all types of studies that may be relevant to their question. They included studies in their review that looked at specific blood types, used or observed a specific diet as an intervention and then looked at health outcomes like BMI, disease incidence or any other quantifiable health outcome.
- The researchers could find only one study that met their question and inclusion criteria.
- There one study was from 1997 (coincidentally), where researchers examined the effects of a low-fat diet on LDL-cholesterol concentrations of study participants grouped according to MNS blood type. The researchers found that there were slight differences in LDL concentrations based on their MNS blood type. Specifically, they found that blood types MM and NN had decreased LDL concentrations, while MN did not after a low-fat diet.
- The researchers could find no studies showing an association between ABO blood type diets and health outcomes.
The researchers concluded,
“There is currently no evidence that an adherence to blood type diets will provide health beneﬁts, despite the substantial presence and perseverance of blood type diets within the health industry.”
Blood type diets are highly popular, and there is a sizable industry backing the promotion of these types of diets. However, until there is good evidence that blood type diets improve particular health outcomes, consumers need to be warned that for now, blood type diets are based on theory and not evidence.
In the present systematic review, researchers could only find one study that examined the effect of a dietary intervention on different blood types. It was a small study from over 15 years ago. Furthermore, the blood types examined (MNS) are not the same blood types that are popularly promoted as needing specific diets (ABO).
We need studies examining the effects of specific diets on ABO blood types before we can make claims or promote blood type diets; specifically studies in the form of randomized controlled trials. Peter D’Adamo published his book and theory in 1997, and there has been little effort to substantiate his claims and carry out research in the area. Thus, it seems unlikely that there will be research validating blood type diets anytime soon.
Until research is carried out, consumers should clearly understand that blood type diets are based on theory and not evidence and proceed at their own discretion.
Leila Cusack, Emmy De Buck, Veerle Compernolle, and Philippe Vandekerckhove. Blood type diets lack supporting evidence: a systematic review. Am J Clin Nutr 2013 98: 1 99-104; First published online May 22, 2013. doi:10.3945/ajcn.113.058693