Eat Right For Your Type: The blood group diet – an update

Lyn Blythe, Medical Herbalist

Dr. Peter D’Adamo, an American naturopathic physician, created The Blood Type Diet - a way of eating which he claims has improved the health of many. He has written numerous books on the subject, and his website can be found here.

Foodsmatter already have an article about this diet, written by Tom Greenfield and Roger James some time ago, but I figured it was time to review the latest literature and write an update.

A brief overview of the Eat Right For Your Blood Type diet.

Dr D’Adamo believes we should eat according to our blood type and our race in order to optimise health.

Blood type O are said to be descended from hunter-gatherers, and to have high levels of stomach acid. According to Dr D’Adamo, they should eat lean meat, poultry, fish, fruits, vegetables, whilst limiting grains and dairy. They should take more vigorous exercise.

Blood type A people are said to be descended from those who cultivated crops, so are thought to be well-adapted to digest all types of plant food. The diet suggests they should eat more soy-based foods, grains, organic vegetables, and take gentle exercise.

Blood type B are thought to be descendants of nomadic tribes, raising herds of animals, so are thought to be efficient meat-digesters. They should eat dairy, meat, corn or wheat, whilst avoiding beans. They should take moderate exercise.

Blood type AB were produced by a mixing of type A and B, so are said to have the digestive advantages of both. They should eat seafood, tofu, dairy, whilst limiting chicken, beef and pork. They are advised to do more calming exercise.

Dr Oz

Dr Mehmet Oz (MD), of the “Dr Oz show” in the USA, has been quoted as saying that eating for his blood type gives him more “vital energy”.  A dietitian has given her views on the diet on Dr Oz’s website, which those interested can find here.

What is the proposed connection between blood type, diet and health?

Dr D’Adamo cites research to support his belief that blood group antigen molecules on the surface of blood cells serve as an energy source for micro-organisms in the gut (Hoskins, 1976).

Dr D’Adamo believes that people with different blood types have correspondingly differing populations of bacteria in their guts. He postulates that these differing microbiomes persist from ancient adaptations to available food supplies as people migrated to different regions. Furthermore, he states that failing to eat according to your blood type leads to incomplete digestion, fuelling “bad” gut bacteria, promoting their growth and numbers, at the expense of “good” bacteria. Considering the immense importance of a healthy gut flora to our digestion and health, this would then be expected to have significant adverse consequences.

Dr D’Adamo reports that when people with an overgrowth of harmful bacteria in the small intestine were changed to a blood group diet, they improved within 6 weeks. He reports success with conditions as far reaching as psoriasis, fatigue and autoimmune thyroiditis.


Many case histories detailing success are included on Dr D’Adamo’s website and in his literature, but is there any independent supporting evidence or reports of success?

Although I was unable to find any independent clinical trials conducted on this diet, there is indeed research suggesting that blood group is one of many factors which modulates the composition of gut flora (Makivuokko, et al, 2012). Moreover, there is a wealth of evidence supporting the significance of blood group to many areas of health (and illness) far beyond mere matching for a blood transfusion.

The biological significance of blood group to health

Secretors and nonsecretors

Whether a person is a secretor or nonsecretor is genetically determined. The majority of people are secretors, ie. secrete antigen molecules corresponding to their blood group into their secretions and tissues. For example, secretors have more blood antigen molecules in their intestinal secretions, this in turn affects the ability of certain bacteria to adhere to the lining of the gut (Szulman, 1960; Pizzorno, 2006).

Nonsecretors have lower alkaline phosphatase activity in the gut, an enzyme involved in breakdown of dietary cholesterol and the absorption of calcium. In addition to secretor status, blood group O individuals have the highest alkaline phosphatase activity, and group A with the lowest.

Nonsecretors have lower levels of some antibody molecules, involved in defence mechanisms in the body. They also appear to have a higher prevalence of autoimmune conditions. Such as ankylosing spondylitis and multiple sclerosis (Shinebaum, 1989; Pal, 1998).

Gastric acidity

Pernicious anaemia and gastric cancer appear to be more common in people of blood group A, and duodenal ulcers more common in blood group O. This may be related to higher gastric acid output in those with blood group O, as compared to A (Vogel, 1970; Waft, 1979; Kuipers, 1995).

Cardiovascular disease

It has been reported that people with blood groups A and AB have a tendency towards problems associated with blood clotting (such as heart attack and stroke), whilst those with groups B and O appear to be more susceptible to poor clotting and “bleeds” (Pizzorno, 2006; Ionescu, 1976).


Tumour development usually involves alterations to carbohydrates on the cell surface. These changes facilitate progression of the tumour cells to more invasive forms. Many studies suggest there is an alteration of blood group antigen expression on the surface of some tumour cells (Lin, 1992; Larena, 1995).

Blood groups and dietary lectins

Lectins are carbohydrate-binding dietary proteins, found in plants and animals (Power, 1991; Freed, 1999). They can influence the composition of gut bacterial flora. It has been stated that most lectins resist degradation in the small intestine, surviving passage through the digestive tract largely functionally intact. There is evidence to support the belief that lectins which cross the gut wall into the systemic circulation can affect hormone balance and immune function (Pusztai, 1993). They can cause intestinal damage, disrupted digestion and nutrient deficiencies in sensitive individuals, and some lectins are blood-type specific (Power, 1991).

Criticism of the diet

Unsurprisingly, perhaps, there is also criticism of the diet.

Dr D’Adamo’s reasoning behind the development of the separate diets is based on evolutionary appearance of blood types. However, his dating of the appearance of the blood types has been disputed. It has been proposed that this, in turn, would then call into question the foods described as appropriate for each blood type (Cordain, 2010). The diet has been criticised for being complicated to understand, and lacking in nutrients for some blood groups (Cordain, 2010; Bonci, 2011).

A further criticism of the diet is that much of the supporting information comes from people who gain monetarily from recommending it, not least Dr D’Adamo himself! This was certainly my difficulty when writing this piece. I also found a couple of references Dr D’Adamo has cited as supporting his claims, which, in my opinion, did not appear to do so, specifically regarding blood group diet and infertility.

In conclusion

So, what is my view of the blood group diet now I have reached the end of my review?

In all honesty, I didn’t expect to find much physiological substance behind the reasoning, however, what I have read has certainly given me “food for thought”. Whilst writing this article, I have spoken to several people about the blood group diet. Interestingly, those who have tried it believe their health has benefitted, and their symptoms have improved - although this is hardly going to be a statically significant survey!

My own conclusion for someone with symptoms considering trying the blood group diet is to try it, if it is safe for them to do so. However, it may be wise to invest in the assistance of a trusted professional if they wish to continue on the diet for a more prolonged period of time.


Bonci, L. (2011). Eat right for your type. Available here. [Accessed 13th February, 2013].

Cordain, L. (2010). Does the eat right for your blood type really work? Available here. [Accessed 13th February, 2013].

Hoskins, L.C., Boulding, E.T. (1976). Degradation of blood group antigens in human colon ecosystems. A gene interaction in man that affects the fecal population density of certain enteric bacteria. J Clin Invest 57: 74-82

Kuipers, E.J., Thijs, J.C., Festen, H.P. (1995). The presence of Helicobacter pylori in peptic ulcer disease. Alimentary Pharmacology & Therapeutics 9 Suppl 2: 59-69

Ionescu, D.A., Marcu, I., Bicescu, E. (1976). Cerebral thrombosis, cerebral haemorrhage, and ABO blood-groups. Lancet1 (7954): 278-280

Freed, D.L.J. (1999). Do dietary lectins cause disease? BMJ 318: 1023

Larena, A., Vierbuchen, M., Fischer, R. (1995). Blood group antigen expression in malignant tumors of the thyroid: a parallel between medullary and nonmedullary carcinomas. Langenbecks Arch Chir 380: 269-272

Lin, X.S. (1992). The expression and significance of blood group antigens (BGA) A,B,H, Le(a) and Le(b) in hepatocellular carcinoma and chronic hepatitis. Zhonghua Bing li xue za zhi Chinese Journal of Pathology 21 (1): 24-26

Makivuokko, H., Lahtinen, S.J., Wacklin, P., Tuovinen, E., Tenkanen, H., Nikkila, J., Bjorklund, M.,  Aranko, K., Ouwehand, A.C., Matto, J. (2012). Association between the ABO blood group and the human intestinal microbiota composition. BMC Microbiology 12: 94

Pal, A., Hill, M., Wordsworth, P., Brown, M. (1998). Secretor status and ankylosing spondylitis. J Rheumatol 25: 318-319

Pizzorno, J.E. & Murray, M.T. (2006). Textbook of natural medicine, 3rd Ed. Missouri: Churchill Livingstone P441-460

Power, L. (1991). Dietary lectins: Blood types and food allergies. Townsend letter for doctors

Pusztai, A. (1993). Dietary lectins are metabolic signals for the gut and modulate immune and hormone functions. Eur J Clin Nutr 47 (10): 691-699

Shinebaum, R. (1989). ABO blood group and secretor status in the spondyloarthropathies. FEMS Microbiol Immunol 1: 389-395

Szulman, A.E. (1960). The histological distribution of blood group substances A and B in man. JEM 111 (6): 785-800

Vogel, F. (1970). Controversy in human genetics. ABO blood groups and disease. Am J Hum Genet 22 (4): 464-475

Waft, L., Roberts, N.B., Taylor, W.H. (1979). Hereditary aspects of duodenal ulceration: pepsin 1 secretion in relation to ABO blood groups and ABH secretor status. J Med Genet 16: 423-427

First published in March 2013


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