June 1991
Laura Power, PhD.
Abstract
Dietary lectins in excess can cause 3 major physiological effects: gastrointestinal damage, Type 2 IgG immune responses, and hemagglutination. Findings include 119 lectins: 54 are panhemagglutinins; 65 are blood-type specific. Herein may lie a method for predicting food sensitivities by ABO blood type.
Introduction
Dietary lectins are protein antigens which bind to surface glycoproteins (or glycolipids) on erythrocytes or lymphocytes. (1) They function as both allergens and hemagglutinins. (2) They are found in plants and animals, and are present in small amounts in 30% of American foods, more so in a whole-grain diet. (2)
Lectins have potent in vivo effects. When consumed in excess by sensitive individuals, they can cause 3 primary physiological reactions: Lectins can cause severe intestinal damage, disrupting digestion and causing nutrient deficiencies. (3) They can provoke IgG and IgM antibodies causing Gell-Coombs Type 2 food allergies and other immune responses. (3,4) And they can bind to erythrocytes, simultaneously with immune factors, causing hemagglutination and anemia. (5) Of the 119 known dietary lectins, about half are panhemagglutinins, clumping all blood types. The remainder are blood-type specific. In general, lectins alter host resistance to infection, cause failure to thrive, and can even lead to death in experimental animals. (2)
Discussion
A review of the literature indicates that there are presently 119 known lectins in edible foods, 54 panhemagglutinins, and 65 lectins specific for blood types A, B, O, AB, M or N, and subtypes A1 or A2. These are present in 30% of American foods. (2)
Are Lectins Harmful?
Lectin toxicity depends on degradation and absorption. Many lectins are resistant to heating, digestion and food processing (9), allowing about 1%-5% to absorb into the blood. (3) Further, lectins are a danger when consumed in their raw state, or by persons deficient in stomach acid, proteolytic enzymes, or Secretory-IgA.
Research indicates that, when consumed in excess by sensitive individuals, lectins can cause 3 detrimental physiological effects. Lectins can cause severe intestinal damage, disrupting digestion, causing protein loss and growth retardation (3), blocking glucose uptake and insulin receptors (10,11), contributing to Celiac Disease (10), and promoting the growth of harmful bacteria. (13) They can provoke numerous immune responses, including IgG and IgM (3,4), sometimes IgE (3), and lymphocyte mitogenesis. (1) Finally, they can agglutinate erythrocytes leading to anemia, sometimes with ABO specificity. (4,12) In general, lectins can cause immune system exhaustion and failure to thrive. (2)
The irony of this is that high-lectin diets are also high-fiber and wholegrain diets, which contain more nutrients needed for better health. High-fiber diets have been associated with low incidence of bowel cancer, ischaemic heart disease, and diabetes. (10)
Can Food Sensitivities Be Predicted by Blood Type?
YES and NO. With blood-type specific lectins, hemagglutination is bloodtype specific, but antibody response is not truly specific. (4,5) For example: In a sensitive type A1 person exposed to excess lima bean, the lectins and antibodies will both bind to the erythrocyte. However, in other persons, the lectins and antibodies may bind together in an immune complex. This means that the type A1 person will suffer more humoral damage, including some anemia. But other persons might be susceptible to tissue damage from immune complexes. Thus the answer is, if lectins absorb: YES. Gell-Coombs Type 2 lectin allergies and hemagglutination can be predicted by blood type in susceptible individuals. HOWEVER, this does not mean that persons with other blood types will have no immune response. Some other persons may have a Type 3 immune response, butthey will have no hemagglutination.
Future Research
Further research is needed to identify more dietary lectins. In addition, research is needed to identify evolutionary patterns in diet, in order to reduce the incidence of digestive distress and food allergies. We are presently conducting three epidemiological studies which match blood types to food allergies.
