Is Tomato Bad for Blood Type B? Separating Fact from Diet Fad

October 26, 2025 •

4 min read

In 1996, the publication of the book Eat Right 4 Your Type introduced the controversial blood type diet, which specifically advises individuals with blood type B to avoid tomatoes. The premise suggests that specific proteins called lectins, found in certain foods, can be harmful based on a person's blood type. However, a growing body of scientific evidence questions the legitimacy of this diet plan.

Quick Summary

The blood type diet theory suggests tomatoes are problematic for type B individuals due to lectins, but scientific evidence overwhelmingly lacks support for these claims. Nutrition experts state no proof links blood type to dietary needs, and any health improvements likely stem from overall healthier eating. The diet is considered restrictive and unsubstantiated.

Key Points

Blood Type Diet Theory: The premise that certain food lectins are incompatible with specific blood types is not supported by scientific evidence.
Tomatoes are Safe for Most: For the majority of people, regardless of blood type, tomatoes are a nutritious and healthy addition to a balanced diet.
Lectins are Overstated: The negative effects of lectins are often exaggerated, and cooking or digestion typically renders them harmless.
Diet Effectiveness Questioned: Any positive health outcomes from the blood type diet are likely from general healthier eating, not the blood type-specific rules.
Focus on Balanced Nutrition: Evidence-based nutrition emphasizes a varied diet of whole foods over restrictive plans based on blood type.
Consult a Professional: It is best to consult a healthcare provider or registered dietitian for dietary advice, not rely on unsubstantiated diet trends.

Understanding the Blood Type Diet and the Tomato Claim

The blood type diet, popularized by naturopath Peter D'Adamo, is based on the idea that each blood type, O, A, B, and AB, has evolved with distinct dietary needs. D'Adamo claims that foods containing specific proteins called lectins can be incompatible with a person's blood type, leading to a range of health issues from digestive problems to chronic disease. For blood type B, he advises avoiding foods like corn, wheat, lentils, peanuts, and specifically, tomatoes. The theory suggests that tomato lectins can cause issues for type B individuals, potentially causing inflammation or affecting metabolism.

The Lack of Scientific Validation

Despite its popularity, the blood type diet lacks support from the broader scientific and medical community. Numerous comprehensive reviews have found no scientific evidence to validate its claims. A 2013 systematic review published in the American Journal of Clinical Nutrition found no studies that demonstrated the health benefits of following a diet based on ABO blood types. A subsequent 2014 study in PLoS One also found no significant interaction between blood type diets and cardiometabolic risk factors. This means that positive health outcomes reported by some followers were likely due to adopting generally healthier habits, like reducing processed foods, rather than following a specific blood type-based protocol.

The Truth About Lectins in Tomatoes

The central claim of the blood type diet rests on the role of lectins. While some lectins can cause issues, the danger is often overstated. Most lectins are rendered harmless by cooking, and others are simply broken down by the digestive process. The idea that specific food lectins agglutinate (clump) blood cells in certain blood types has not been proven. Furthermore, a healthy, varied diet includes many lectin-containing foods without causing harm. Experts, like registered dietitians, point out that eliminating nutritious whole foods unnecessarily is a major drawback of the blood type diet. The notion that tomatoes cause inflammation or arthritis is another persistent myth that is not backed by research.

Blood Type B Diet: Claims vs. Facts

While the blood type diet makes specific recommendations for type B, it is crucial to understand the lack of evidence supporting them. The following table compares the diet's claims with the scientific consensus on tomatoes and overall diet.


Feature	Blood Type Diet Claim (Type B)	Scientific Consensus	Is Tomato Bad for Blood Type B?	Tomato Benefits for All Blood Types
Dietary Focus	Mix of meat, dairy, and plants; avoid specific lectin-heavy foods.	Focus on balanced, varied whole foods, regardless of blood type.	No, there is no scientific evidence that tomatoes are bad for blood type B individuals.	Rich in Vitamin C, antioxidants, lycopene, and potassium.
Tomato Consumption	Eliminate completely to avoid negative lectin interactions.	Safe and nutritious for the vast majority of people.	The claim is based on an unsubstantiated fad diet, not evidence-based nutrition.	Can support immune system, vision, skin health, and digestive health.
Health Impact	Claimed benefits include reduced inflammation and improved metabolism.	Restrictive diets can lead to nutrient deficiencies.	Concerns about lectins causing harm are not scientifically supported.	Anti-inflammatory properties are attributed to antioxidants.

Potential Downsides of Restrictive Diets

Following a restrictive diet like the blood type diet can have potential downsides. Eliminating entire food groups without a medical reason can lead to nutrient deficiencies. For example, if someone unnecessarily avoids nutrient-dense foods like tomatoes, they might miss out on essential vitamins and antioxidants. Moreover, creating a strict dietary plan based on an unproven theory can be mentally taxing and make meal planning difficult, especially within a family with different blood types. It is always recommended to consult a doctor or registered dietitian before making significant changes to your diet.

A Better Approach to Diet and Wellness

Instead of focusing on scientifically debunked theories like the blood type diet, a better approach is to adopt general healthy eating principles. This involves incorporating a variety of fruits, vegetables, lean proteins, and whole grains, while limiting processed foods and unhealthy fats. Personal health history, any diagnosed conditions, and individual food intolerances are far more relevant factors for dietary choices than blood type. For most people, tomatoes are a healthy, nutritious food that provides numerous benefits, such as supporting heart health and providing essential vitamins. The best diet is one that is balanced, sustainable, and tailored to individual needs in consultation with a healthcare professional.

The Takeaway on Tomatoes and Blood Type B

Ultimately, the idea that tomato is bad for blood type B is a misconception rooted in a diet that has been widely refuted by the scientific community. The claims about lectins causing harm in specific blood types are not supported by evidence. For the vast majority of people, regardless of their blood type, tomatoes are a valuable part of a healthy and balanced diet. Instead of cutting out whole, nutritious foods, focus on a varied eating plan and listen to your body.

Conclusion: Focus on Evidence-Based Nutrition

The assertion that tomato is bad for blood type B stems from the scientifically unproven blood type diet. While proponents argue that certain food proteins, or lectins, cause adverse reactions, systematic reviews and independent studies have found no evidence to support these claims. On the contrary, tomatoes are a nutrient-dense food rich in antioxidants, vitamins, and minerals that offer health benefits for everyone. Rather than adhering to restrictive fad diets, a more effective and sustainable approach to health involves focusing on a balanced, varied diet of whole foods based on scientific consensus, individual tolerance, and professional medical advice. It is important to separate nutritional fact from dietary fiction and make informed choices for long-term well-being.

Note: Always consult with a healthcare professional or registered dietitian before making significant changes to your diet.

Frequently Asked Questions

No, the blood type diet is not scientifically proven. Multiple systematic reviews and studies have found no evidence to support the theory that eating based on your blood type improves health or prevents disease.

The diet claims that tomatoes contain lectins that can have a negative effect on blood type B individuals. This is part of the diet's broader, unsubstantiated theory about lectin compatibility with specific blood types.

For most people, the lectins in tomatoes are not harmful. Cooking tomatoes typically destroys these proteins, and the digestive system effectively neutralizes most others.

Tomatoes are a great source of vitamins like C and K, and minerals like potassium. They also contain powerful antioxidants, such as lycopene, which are beneficial for heart health and can have anti-inflammatory effects.

Yes, following a highly restrictive diet without medical justification, such as the blood type diet, can increase the risk of nutrient deficiencies by cutting out otherwise healthy and nutrient-dense foods.

It is not recommended to follow the blood type diet. While some people may experience positive effects, these are likely a result of eating fewer processed foods, not their blood type. A balanced diet focusing on whole foods is a more evidence-based and sustainable approach to health.

Your dietary needs should be determined by factors such as your overall health, individual intolerances, activity level, and professional medical advice. Consulting a doctor or registered dietitian is the best way to get personalized nutritional guidance.