The blood type diet was created by Peter D’Adamo and James D’Adamo and was popularised in the best selling book ‘Eat Right 4 Your Type’, originally published in 1996. The diet is based on matching the foods consumed to the type of antigens present on the surface of an individual’s red blood cells using the type ABO blood grouping system. Theses antigens on the surface of red blood cells are controlled by the A, B and O genes on chromosome 9 and are important because they are required to be taken into account during blood transfusions. The theory proposed by the authors of ‘Eat Right 4 Your Type’ is that lectins, protein-like substances within food which are obtained from animal and plant foods, can cross react with certain antibodies within the ABO blood grouping system. Although around 95 % of the lectins in foods are destroyed during cooking and during digestion, the remaining 5 % of the lectins may be absorbed where they can interact with the antibodies in the blood of the individual, leading to chronic inflammation.
Some of the lectins in the diet may therefore be incompatible with the blood of individuals because they react with antibodies. Eating the wrong foods, the theory suggests, therefore can produce a reaction that is treated like an invading pathogen, and may cause stimulation of the immune system and a typical inflammatory reaction. The theory suggests that those with type O blood are more closely related to our early ancestors and these individuals do better on a diet of animal flesh and vegetables. Type A blood is theorised to have developed when early agriculture began. Such individuals do better by basing their diet on a plant based diet containing vegetables, legumes and whole grains with very occasional poultry or fermented dairy products. More variety is encouraged in those with type B blood who can tolerate meat, dairy, whole grains and shellfish. Type AB blood is theorised to have developed as early civilisation flourished and individuals with type AB blood can tolerate most foods except smoked and cured meats.
Around 7 million copies of ‘Eat Right 4 Your Type’ were sold and the book has been published in more than 60 languages. However despite the book’s popularity, the nutritional literature does not contain evidence to support the claims made within the book. For example, in a recent review of the relevant studies1, researchers investigated the claim of the book using previously published research. However, the authors only found 1 relevant article and this paper investigated not the ABO system of blood grouping, but the MNS system. Further, this study only measured the low density lipoprotein response to a low fat diet. The conclusions of the researchers was that they were not able to answer their original question ‘In humans grouped according to blood type, does adherence to a specific diet improve health and / or disease risk compared to non-adherence to the diet?’ Therefore we can conclude from this that there is no evidence to support the contention that eating a specific diet for your blood type is advantageous.
The scientific literature does not support or refute the efficacy of the blood type diet. Based on the popularity of the book, it is surprising that no studies have been funded to investigate this issue. However, thinking about the diet logically we can see that the diet does vastly oversimplify the blood grouping system. At present over thirty markers are known to be present on red blood cells and a number of blood grouping systems are in place. Another problem with the diet is that it is claimed that dietary lectins are absorbed, and this may not be correct. However, there are a number of studies that have looked at the influence of lectins in disease and evidence does support a role for some lectins in some disease processes. Perhaps a better way to look at this diet is to stand back and agree that we are all genetically individual and that eating different diets is likely a necessity based on out very different tolerances and metabolisms. Whether these differences can be satisfied by a prescription from a book, or whether trial and error is the best tactic to identify a suitable diet is perhaps something the individual should decide for themselves.
RdB
