Understanding the Blood Type Diet
The blood type diet, created by naturopathic doctor Peter D'Adamo, is a nutritional plan based on the premise that a person's blood type (A, B, AB, or O) determines which foods they should eat and which they should avoid. The core theory is that lectins, a type of protein found in many foods, can react negatively with the antigens of certain blood types, causing health problems like digestive issues and inflammation. D'Adamo's theory positions Type O blood as the 'hunter' type, with an ancestral diet high in animal protein. Following this logic, foods introduced more recently in human history, such as grains and dairy, are considered incompatible. However, it is crucial to note that modern scientific research has largely debunked these claims, finding no evidence to support the diet's effectiveness or the underlying evolutionary assumptions. The diet's popularity is often attributed to its emphasis on whole foods and reduced intake of processed items, principles which are generally healthy for everyone, regardless of blood type.
Foods to Avoid for O+ People Based on the Theory
For those interested in the specifics of the blood type diet theory, D'Adamo's recommendations outline several food groups and individual items that Type O individuals should avoid or limit. These restrictions are based on the unproven idea that they may interfere with digestion or lead to weight gain.
Grains and Wheat Products
According to the diet, wheat and most grains are lectin-heavy and should be avoided by Type O individuals. This includes a wide range of common foods:
- Wheat and whole wheat products (bread, pasta, bulgur, flour)
- Corn and corn products (cornmeal, cornstarch, corn syrup)
- Oats and oatmeal
- Seven-grain flour
- Graham flour
Dairy and Eggs
Dairy products are also a major point of restriction for Type O blood types. The theory suggests that these individuals may have trouble digesting dairy, and consumption could lead to inflammation and weight gain. While some cheeses are occasionally permitted, the general recommendation is to avoid most dairy and eggs.
- Milk (cow's milk)
- Most cheeses, yogurts, and butters
- Ice cream
Legumes
The diet posits that certain legumes can interfere with the metabolism of Type O individuals and cause weight gain.
- Kidney beans
- Lentils (all types)
- Navy beans
- Certain other beans, like copper beans and tamarind
Specific Vegetables and Fruits
While the Type O diet is generally high in vegetables, some specific items are listed as potentially harmful.
- Cabbage and cauliflower (may inhibit thyroid function)
- Brussels sprouts
- Avocados (high in fat, supposedly not ideal for Type O)
- Corn (listed under grains but also a vegetable)
- Melons (cantaloupe, honeydew)
- Oranges and tangerines
- Strawberries and blackberries
- Rhubarb
- Coconuts and coconut products
Beverages and Condiments
Certain drinks and common kitchen items are also on the 'avoid' list based on the theory.
- Coffee and black tea (high caffeine)
- Alcohol (especially distilled liquor and beer)
- Vinegar and pepper
- Ketchup, mayonnaise, and pickles
Scientific Critique of the Blood Type Diet
Despite the specific recommendations, a wide consensus in the scientific and medical community refutes the blood type diet. Multiple studies have found no scientific basis for its claims. A 2013 systematic review found no evidence to validate the health benefits associated with the diet. In a 2014 study published in PLOS One, researchers found that while participants on the Type A diet showed some improved health markers, this was not dependent on their actual blood type. The same study found that the Type O diet also had some benefits, but again, these were independent of blood type and likely related to adopting healthier eating habits. Experts point out that the diet's elimination of processed foods, unhealthy fats, and simple sugars, coupled with increased intake of fruits and vegetables, is what drives any positive health outcomes. The theory about lectins causing blood cell clumping is also largely unproven and oversimplified.
Comparative Table: Blood Type Diet Theory vs. Evidence-Based Consensus
| Food Category | Blood Type Diet (O+) Theory | Evidence-Based Nutritional Consensus |
|---|---|---|
| Grains | Largely forbidden (e.g., wheat, corn), due to lectin theory and ancestral diet assumptions. | A crucial part of a balanced diet, especially whole grains, which provide fiber, vitamins, and minerals. Individual needs may vary (e.g., gluten intolerance), but not based on blood type. |
| Dairy | Severely restricted, believed to be difficult to digest for Type O. | A good source of calcium, protein, and Vitamin D for many people. Intolerance is related to lactose digestion, not blood type. Alternatives exist for those with intolerance. |
| Legumes | Avoided or limited (e.g., lentils, kidney beans) due to lectin theory. | Excellent sources of plant-based protein, fiber, and iron. Highly recommended for overall health by dietitians. |
| Protein | Emphasizes a high-protein intake, especially lean meat. | Balanced intake of lean proteins (including meat, fish, and plant-based sources like legumes and nuts) is recommended. Excessive red meat is not universally beneficial. |
| Overall Approach | A highly restrictive, pseudo-scientific diet based on blood antigens and evolutionary theory. | Focuses on a varied diet rich in whole foods, tailored to individual health needs, preferences, and medical history, not blood type. |
Conclusion: Making Informed Dietary Decisions
While the idea of a diet tailored to your blood type is compelling, the scientific evidence to support the notion that what foods should O+ people avoid based on their blood type is nonexistent. Medical professionals and nutritionists do not endorse the blood type diet as a valid or proven method for improving health. Any perceived benefits are likely due to the general health improvements that come from reducing processed foods, sugars, and unhealthy fats, and increasing intake of fruits and vegetables. Before making any significant changes to your diet, it is always best to consult with a healthcare provider or a registered dietitian. They can provide guidance based on scientifically backed evidence, your personal health profile, and specific nutritional needs. Ultimately, a balanced and varied diet, rather than one restricted by an unproven theory, is the most reliable path to long-term health and wellness.
Visit Healthline for more on the lack of evidence supporting the blood type diet.
Frequently Asked Questions
What does the O positive diet suggest regarding grains like wheat and corn?
According to the diet's theory, O positive individuals should avoid most grains, including wheat and corn, as they contain lectins that are believed to be incompatible with their blood type.
Are dairy products completely forbidden for O+ blood types?
The diet's theory advises Type O individuals to severely restrict or avoid dairy products, as they are considered difficult to digest and potentially inflammatory.
What about legumes like lentils and kidney beans for O+ blood types?
For O+ individuals, the blood type diet advises avoiding legumes such as lentils and kidney beans, based on the theory that they can interfere with metabolism.
Is there any scientific evidence that the blood type diet is effective?
No, there is no scientific evidence to support the claims of the blood type diet. Multiple systematic reviews and studies have found no link between blood type and optimal dietary recommendations.
Why do some people report feeling better on the O blood type diet?
Any positive health effects are likely due to the general improvement of adopting a healthier eating pattern, such as consuming more whole foods and fewer processed items, rather than from adhering to the blood type-specific rules.
Should the Rh factor (positive or negative) be considered in the blood type diet?
The creator of the blood type diet, Peter D'Adamo, does not specify the Rh factor as playing a significant role in the diet's recommendations.
Is it safe to follow a highly restrictive diet based on blood type?
It can be risky to follow a restrictive diet based on unsupported theories without consulting a healthcare professional, as it may lead to nutritional deficiencies.
How does the scientific community view the blood type diet?
The majority of the scientific and medical community considers the blood type diet to be a fad diet lacking scientific merit, and it is not widely endorsed by health professionals.
What are some commonly avoided fruits for O+ blood types on this diet?
Fruits to be avoided or limited, according to the blood type diet, include oranges, strawberries, cantaloupe, and coconuts.
According to the theory, why should O+ individuals avoid coffee?
Based on the theory, O+ individuals should avoid coffee and other caffeinated beverages because they may be more sensitive to caffeine's stimulating effects, which can increase adrenaline levels.
Does the O+ blood type diet recommend avoiding alcohol?
The diet's theory recommends that O+ individuals avoid alcohol, specifically beer and distilled liquor.
