Dr. Nadeau's Criticism

Michèle Houde Nadeau, D. Sc.
Titular professor
Nutrition Department
Faculty of Medecine
University of Montreal
September 5, 1999

State of the matter :

Peter J. D’Adamo1, naturopath, strongly recommends the adoption of a specific diet based on blood type (A, B, AB, and O). Mr. D’Adamo relies on the subjective observations of his father, also a naturopath, to foster his interest on the prevailance of some diseases according to blood type. He reviews articles published on this subject et obtains confirmation of the existence of such a link for some pathologies, more specifically for the stomach ulcer and cancer. Making reference to some anthropological notions, Mr D’Adamo notes that blood type diversication happened gradually through tim and suspects that the emergeance of new blood types is a result of man’s adaptation to his environment, including nutrition. He concludes from this that some diets are more appropriate to each blood type.

We already knew some elements, called lectins, could be used in laboratory to identify blood types. Lectins, present in plants, are composed of a wide variety of proteins that bind themselves to glucides attached to the red blood cells membranes, such glucides being different in nature according to blood type2. Researchers have later discovered that food lectins could have toxic impacts under some circumstances. An accute intoxication case on humans has been reported in 19883. Mr D’Adamo concludes from this that chronical intoxications with lectins would be responsible for chronical diseases prevailing in the general population. According to him, lectins would only affect negatively those subjects sensitive to given lectins according to their blood type.

Based on these assumptions and on natural nutrition principles, he establishes diets for each blood type, diets that are also adapted according to ancestral types (African, Asian, Caucasian).


1.      The author : Mr D’Adamo is a naturopath who has some notoriety among his pairs and the general public. His well known enthusiasm however leads him to give to some established findings a bearing largely based on speculation.

2.      Blood type and diseases : The research on the relationship between blood types (A, B, AB and O of red cells) and diseases has been very intense in the fifties and sixties. Some relationships have been established4. This should not surprise anyone since blood types, as well as susceptibility to some diseases, are linked to the genetical heritage. However, we now know many other antigens systems of red blood cells and the progresses of genetics are directing research more on human leucocytes antigens (HLA) 5, who express the individual immunogenetic differences, rather than on blood types (ABO).

3.      Lectins :

-          In laboratory :

The wide variety of lectins found in nature and the specificity of their link with glucides present onto the surface of cells, including red blood cells, makes of them tools used in laboratories to identify blood types. This identification can be made when a blood sample has been processed according to a precise protocol to expose to the lectins the glucides susceptible to react. In the intact organism, these glucides are masked by protective substances that subtract them to the effect of lectins.

-          In food :

The food lectins present in most plants, more specifically in cereals, tubers and beans, are largely inactivated by digestive enzymes. A fraction however escapes from this destruction. They may then affect the digestive tract, leading to multiplication of cells or, if lectins are very abundant, cause the rupture of cells and modifye the permeability of the intestin5. It has been suggested, but not demonstrated, that gluten intolerance (wheat protein) might be caused by some lectins present in this cereal6.

The lectins going through the circulatory system (by means of endocytosis) could also bind themselves to the glucides of smooth muscle (blood vessel lining, renal tubuli, …) and stimulate their proliferation7. They could stimulate the expression of antigens potentially capable of damaging cells of the thyroid or of the pancreas8 (Lancet, 1985), or bind themselves to various membrane receptors and cause other problems of toxicity that are still not well known5. This suggests that if the organism did not have any defence mechanism against lectins, the population would be at risk of cardiovascular diseases, renal diseases, diabetes, hypothyroidism, arthritis, etc.

But most of us are protected against lectins effect because the glucides of cellular membranes are protected by molecules of sialic acid. Lectins thus cannot bind themselves to them to impact them. Cells become vulnerable to lectins only when the sialic acid protection is removed, for example under the influence of an enzyme (neurominidase) present in some micro-organisms such as the influenza virus and streptococcus9. This allows to put forward the hypothesis that lectins might be linked to some diseases appearing the following of some infections10.

4.      D’Adamo’s theory : Interactions food/blood types/pathologies

What do we know about the people’s sensitivity to foods according to a specific blood type (ABO)? Almost nothing. There is indeed no data base, even partial, on this subject. Left alone is a British study11, and its results have not been confirmed, reporting that the consumption of 100 g of peanuts increase the cellular multiplication of those tested (n=10) who express the antigen of the Thomsen-Friedenreich blood type in the colon mucous membrane. In this research, no attention has been given to ABO blood types.

We should note that Mr D’Adamo gives as scientific proof of his theory (p. 27) the fact that « he has himself virtually tested the impact of all foods on blood type ». However he does not provide any credible reference for these « tests »; and even if this would be the case, let us remind that one of the first characteristics of scientific data is that they have been validated by several independant research groups.


Chronical diseases and blood types have links based on genetics. The interaction of the genetic potential with nutrition is yet only partially known, and it is possible that lectins could exert variable effects according to the genetic profile of individuals. This hypothesis is even more plausible if we restrict it to specific conditions such as infections. However, the limited knowledge available on physiological or pathological effects of the various lectins, and even less of foods that contain, in addition of lectins, hundreds of elements capable of interacting with them, do not allow for sure to establish a diet that would pretend whatever guarantee of effectiveness.


1.      D’Adamo P.J » with C. Whitney. Eat Right 4 your type. G.P. Putnam’s sons, New York 1996.

2.      Marieb E.N. Anatomie et Physiologie Humaine. Éditions du Renouveau Pédagogique Inc. 1993.

3.      Gilbert R.J. Healthy eating day. Communicable Disease Report. 33 : 3, 1988.

4.      Nijevitch A.A et coll. Childhood duodenal ulcer associated with Helicobacter pylori and ABO blood groups. Amer. J. Gastroent. 94 : 1424, 1999.

5.      Shils M. et coll. Modern Nutrition in Health and Disease. 9ième ed. Lea & Febiger, Londres, 1999.

6.      Weiser M.M. and A.P. Douglas. An alternative mechanism for gluten toxicity in coelia disease. Lancet : 567, 1976.

7.      Kritchevsky and coll. Lectins may contribute to the athrogenecity of peanut oil. Lipids 33 : 821, 1998.

8.      Anonymous. What triggers auto-immunity ? Lancet : 78, 1985.

9.      Uchigata Y. and coll. Pancreatic islet cell surface glycoprotein containing Gal B (1-4) Gnac-R identified by cytotoxic monoclonal antibodies. J. Exper. Med. 165 : 124, 1987.

10.  Freed D.L.J. Do dietary lectins cause disease ? Brit. Med. J. 318 : 1024, 1999.

11.  Ryder S.D. Peanut ingestion increase rectal proliferation in individuals with mucosal expression of peanut lectin receptor. Gastroenterol. 114 : 44, 1999.