The claim that tomatoes are detrimental for individuals with Blood Type B stems from the popular, though controversial, Blood Type Diet (BTD). This theory, formalized by Dr. Peter D’Adamo, suggests that a person’s ABO blood group is the primary determinant of their optimal nutritional needs, weight management, and disease susceptibility. The diet outlines detailed lists of foods that are deemed “highly beneficial,” “neutral,” or “avoid” for each blood type. This article explores the reasoning behind the BTD’s categorization of tomatoes as an “Avoid” food for Type B individuals, examining the proposed biological mechanism and the current scientific perspective on this claim.
The Blood Type Diet and Blood Type B
The Blood Type Diet is founded on the idea that each blood type represents an evolutionary stage with corresponding ancestral eating patterns. According to the theory, Blood Type B is associated with the “Nomad” or pastoralist populations, whose traditional diet was more varied, including meat and dairy. This evolutionary premise is used to justify the specific dietary guidelines for Type B individuals, which are generally more inclusive of different food groups, uniquely permitting most dairy products.
However, the Type B diet also includes a list of foods that are strongly recommended for avoidance due to their perceived incompatibility. These incompatible foods are thought to interfere with metabolism, promote inflammation, and contribute to weight gain. Tomatoes are unequivocally placed on this “Avoid” list for Blood Type B, alongside foods like corn, wheat, peanuts, and sesame seeds.
The diet’s philosophy posits that consuming these incompatible foods creates an adverse reaction unique to the Type B blood group. This negative reaction is believed to stem from specific proteins in the food that interact with the markers present in the blood.
The Proposed Mechanism of Tomato Lectins
The reason for avoiding tomatoes centers on a class of proteins called lectins. Lectins are carbohydrate-binding proteins found in many plant-based foods, especially in seeds and legumes. The BTD claims that certain lectins possess an ability to interact with and bind to the specific carbohydrate structures, or antigens, present on the surface of red blood cells and other body tissues.
For Blood Type B individuals, the central claim is that the lectin found in tomatoes, known as Lycopersicon esculentum agglutinin (LEA), acts as an agglutinin against the B antigen. Agglutination is a process where the lectin acts like a double-sided adhesive, causing red blood cells to clump together. The theory suggests this clumping can occur in the bloodstream, leading to various health problems, including inflammation and compromised organ function.
Furthermore, the BTD hypothesizes that this tomato lectin can resist breakdown by stomach acids and digestive enzymes. Remaining intact, the lectin is then believed to bind to the lining of the digestive tract, causing irritation, and potentially passing into the bloodstream where it can target specific organs. The consumption of tomatoes is thus theorized to cause a form of internal “blood clotting” in Type B individuals due to this specific lectin-antigen incompatibility.
The diet also claims that cooking does not neutralize the lectin activity, and may even enhance it. This resistance to heat is cited as a reason why all forms of tomato, including sauces and pastes, are considered detrimental for Type B individuals.
Scientific Review of the Diet Claims
Despite the popularity and detailed nature of the Blood Type Diet, the scientific and medical communities generally do not support its underlying premises. Multiple systematic reviews have been conducted to evaluate the health benefits of the BTD, concluding that there is no rigorous, peer-reviewed evidence to validate the diet’s effectiveness or its claims of blood type-specific food incompatibility.
The theory that tomato lectins cause blood type-specific agglutination in the human body is not supported by mainstream nutritional science. While lectins exist in tomatoes, the vast majority are broken down by cooking, the digestive process, or eliminated by the body’s immune system. Furthermore, laboratory studies examining the agglutination effects of various plant lectins on human red blood cells have often found that tomato extracts do not cause agglutination in any of the ABO blood types.
Any reported health improvements experienced by individuals following a Blood Type Diet are likely attributable to the elimination of processed foods and the overall shift toward healthier eating patterns, such as increased consumption of fruits, vegetables, and lean proteins. Research has demonstrated that the positive health outcomes associated with following any of the BTD plans are independent of the individual’s actual blood type. For instance, a person with Type B blood may experience benefits from a Type A diet, which is designed to be largely vegetarian, simply because it is a healthier diet overall.
The scientific consensus holds that the specific mechanism linking tomato lectins to an adverse reaction in Blood Type B individuals lacks empirical support. The claim that tomatoes are detrimental for Type B is a theoretical concept within a specific diet, not a finding supported by established human physiology or clinical nutrition research.