What food is not good for O-positive? The Blood Type Diet Explained

January 7, 2026 •

4 min read

According to naturopath Peter D'Adamo, author of the bestselling book 'Eat Right 4 Your Type,' individuals with O-positive blood should avoid certain foods like wheat, dairy, and corn due to ancestral digestive traits. However, major scientific reviews have found no evidence to support the claims of the blood type diet. This article explores the food recommendations for O-positive blood, as proposed by D'Adamo's theory, while acknowledging the lack of scientific backing.

Quick Summary

This article discusses the specific foods, including grains, dairy, and certain vegetables, that the blood type diet suggests O-positive individuals should avoid based on the theory that dietary needs are determined by blood type. It outlines the rationale proposed by the diet's creator and compares these claims with general, evidence-based nutritional guidelines.

Key Points

Blood Type Diet Theory: Proponents of this diet, like Peter D'Adamo, believe a person's blood type dictates their dietary needs due to ancestral evolution and reactions to food lectins.
O-Positive Foods to Avoid: The diet recommends that O-positive individuals, framed as 'hunters,' should avoid grains (especially wheat), most dairy products, certain legumes (like kidney beans and lentils), and corn.
Lack of Scientific Evidence: Extensive scientific research has found no credible evidence to support the health benefits or underlying principles of the blood type diet.
Potential Nutrient Deficiencies: Following the highly restrictive O-positive diet can lead to deficiencies in essential nutrients, like calcium and fiber, found in the restricted food groups.
Focus on Evidence-Based Nutrition: A healthier approach involves a balanced diet of whole foods, lean protein, and a variety of fruits and vegetables, rather than one based on an unproven blood type theory.
Consult a Professional: For personalized dietary advice, it is always best to consult with a healthcare professional or registered dietitian who can provide evidence-based recommendations.

Understanding the Blood Type Diet Theory

First introduced by naturopath Peter D'Adamo, the blood type diet is a nutritional plan that categorizes foods as 'beneficial,' 'neutral,' or to be 'avoided,' based on a person's specific blood type (O, A, B, or AB). The central theory posits that each blood type, corresponding to an evolutionary stage, has a different response to proteins called lectins found in certain foods. According to D'Adamo, the hunter-gatherer ancestry of Type O individuals means they have a high-protein, meat-based metabolism, and their bodies react negatively to lectins in many modern foods.

Foods Suggested to Avoid for O-Positive

Based on D'Adamo's framework, individuals with O-positive blood are advised to limit or completely cut out several food groups. The restrictions are primarily aimed at foods that are supposedly difficult for the 'hunter' digestive system to process, which could lead to inflammation, weight gain, or other health issues.

Grains and Wheat Products

One of the most significant restrictions for the O-positive diet is on wheat and gluten-containing products. D'Adamo's theory claims that lectins in wheat can be inflammatory for those with type O blood, potentially interfering with nutrient absorption and metabolism. Therefore, foods like breads, pastas, cereals, and baked goods made from wheat are often discouraged. Beyond wheat, other grains such as corn, buckwheat, and various types of flour are also on the list of foods to avoid.

Dairy Products

Dairy is another food group that the blood type diet recommends limiting for O-positive individuals. The theory suggests that type O individuals may have difficulty digesting lactose, leading to bloating and other digestive discomforts. This includes milk, most cheeses, yogurt, and other dairy-based products. Dairy alternatives, such as soy or almond milk, are often suggested as substitutes.

Certain Legumes and Beans

While not all legumes are off-limits, some varieties are specifically advised against. This is because proponents of the diet believe that specific lectins found in certain beans can cause issues for the type O digestive tract. The list of beans to avoid typically includes kidney beans, navy beans, and lentils.

Other Miscellaneous Foods

Vegetables: While most vegetables are beneficial, a few are singled out for O-positive individuals. Cabbage, cauliflower, corn, and eggplant are on the 'avoid' list in some blood type diet interpretations due to their lectin content.
Beverages: Some proponents of the blood type diet suggest limiting caffeinated and alcoholic drinks. For instance, coffee and beer are frequently mentioned as items to restrict or avoid.
Specific Fruits: While many fruits are encouraged, certain ones like oranges, strawberries, cantaloupes, and coconut may be classified as less beneficial or to be avoided.

Blood Type Diet vs. Evidence-Based Nutrition

Despite the specific claims, it is crucial to recognize that the blood type diet lacks scientific validation. A 2013 systematic review published in the American Journal of Clinical Nutrition found no evidence to support the purported health benefits of blood type diets. Furthermore, a 2014 study in PLoS One found no association between blood type and the reported health effects of the diet. Experts argue that any health improvements reported by followers are likely due to the diet's general promotion of whole, unprocessed foods and the elimination of common inflammatory agents like processed foods, sugar, and excess alcohol.

Comparison Table: Blood Type Diet vs. Standard Nutritional Advice


Aspect	Blood Type Diet (Type O)	Evidence-Based Nutritional Advice
Dietary Approach	Highly restrictive, based on a single biological marker (blood type).	Flexible and personalized, based on comprehensive health needs, activity level, and individual sensitivities.
Carbohydrates	Strongly discourages grains like wheat and corn, potentially limiting a source of fiber and energy.	Emphasizes whole grains as a key source of energy, fiber, and B vitamins.
Dairy	Avoids most dairy, citing poor digestibility for type O.	Recommends dairy (or fortified alternatives) as a source of calcium, protein, and vitamin D.
Legumes	Avoids certain beans and lentils due to specific lectins.	Includes a wide variety of legumes and beans as excellent sources of fiber and plant-based protein.
Scientific Basis	Primarily based on anecdotal evidence and an unproven theory about lectins and ancestral evolution.	Supported by extensive research on nutrition, metabolism, and chronic disease prevention.
Potential Risks	May lead to nutrient deficiencies due to broad restrictions on major food groups.	Follows guidelines from established health organizations to provide complete nutrition.

What to Consider for a Healthy Diet

Rather than adhering to an unproven theory, a more holistic and scientifically sound approach to nutrition is recommended. This involves creating a balanced, varied, and personalized eating plan. If you are concerned about digestive issues or want to optimize your diet, a registered dietitian can provide evidence-based guidance tailored to your specific health profile, not just your blood type. For instance, someone with type O blood who avoids dairy might need to find alternative sources for calcium and vitamin D, and a nutritionist can help address those gaps. Focusing on whole foods, lean proteins, healthy fats, and a wide array of fruits and vegetables—without the unnecessary restrictions of the blood type diet—is the best path to sustainable health.

Conclusion

While the blood type diet offers a fascinating, albeit controversial, perspective on personalized nutrition, its recommendations for what food is not good for O-positive individuals are not supported by scientific evidence. The diet's restrictions on grains, dairy, and certain legumes are based on an unproven theory about lectins and ancestral digestive systems. For those seeking to improve their health, focusing on a balanced, nutrient-dense diet grounded in mainstream nutritional science is a safer and more effective strategy. Consulting a healthcare professional or registered dietitian is always the best course of action for personalized dietary advice. For further reading on the scientific evaluation of this diet, consider reviewing the systematic review from the American Journal of Clinical Nutrition.

Frequently Asked Questions

The blood type O diet primarily suggests avoiding grains, particularly wheat and gluten products, and dairy products based on the theory that they are poorly digested by those with this blood type.

No, major scientific reviews have found no evidence to support the claims of the blood type diet. Any health benefits reported are more likely linked to eating healthier foods in general, not a person's blood type.

The diet claims that lectins in wheat can cause inflammation and negatively impact the digestive system of O-positive individuals, though there is no scientific proof for this specific blood-type interaction.

Yes, completely avoiding dairy products can increase the risk of deficiencies in important nutrients like calcium and vitamin D. It is important to find alternative sources or supplements if cutting out dairy.

The diet recommends a high-protein, meat-heavy diet for O-positive individuals, focusing on lean meats, fish, vegetables, and certain fruits.

Most health experts do not recommend following the blood type diet due to the lack of scientific evidence and potential for unnecessary dietary restrictions. A personalized, evidence-based approach is generally safer and more effective.

A better alternative is to follow evidence-based eating plans that are balanced and tailored to your individual needs, health conditions, and preferences, such as consulting a registered dietitian or following guidelines from established health organizations.