The Theory Behind the Blood Type Diet
Popularized by Dr. Peter J. D'Adamo in his 1996 book, Eat Right 4 Your Type, the blood type diet is based on the unproven theory that each ABO blood group (A, B, AB, O) evolved from different ancestral eating patterns. According to this hypothesis, people with blood type A, supposedly descended from early farmers, are said to thrive on a vegetarian or plant-based diet. Conversely, the diet suggests that type A individuals have sensitive immune systems and lower stomach acid levels, making it difficult to digest animal proteins effectively. As a result, the diet recommends a number of food exclusions for those with A+ blood to supposedly improve health, energy, and digestion.
Foods to Avoid for A+ Blood Type (According to the Diet)
Based on the blood type diet, individuals with A+ blood should focus on a diet rich in fruits, vegetables, tofu, legumes, and whole grains. The recommendations advise against or suggest limiting several food groups that are claimed to cause digestive issues or promote inflammation in Type A individuals. These include:
Meats and Animal Products
- Red Meat: All red meat, such as beef, pork, lamb, and veal, is strictly off-limits. The diet's premise is that A+ individuals lack the digestive enzymes necessary to properly process these foods.
- Processed Meats: Cured and processed meats, such as bacon, ham, and smoked meats, are also to be avoided.
- Poultry: While some variations are stricter, some recommendations suggest avoiding duck and goose.
- Shellfish: Many shellfish varieties are on the 'avoid' list, including crab, shrimp, lobster, and oysters.
Dairy Products
- Most dairy is recommended for limitation or avoidance, as the diet suggests A+ types have trouble digesting it. Cow's milk, cheese, and butter are generally discouraged.
- However, some fermented dairy products, such as yogurt and kefir, are sometimes allowed in moderation.
Grains and Legumes
- Wheat Products: The diet suggests avoiding most wheat-based foods, such as wheat flour, pasta, and bread, due to claims of agglutinating proteins.
- Beans: Certain legumes, including kidney beans, lima beans, and garbanzo beans, are on the list of foods to avoid.
Specific Fruits and Vegetables
- Fruits: Fruits like mangoes, bananas, and papayas are considered harder to digest and therefore not recommended. Oranges are also on the 'avoid' list.
- Vegetables: Specific vegetables, including potatoes, tomatoes, and cabbage, are sometimes mentioned as incompatible.
Oils, Nuts, and Beverages
- Oils: Certain oils, such as corn, safflower, and cottonseed oil, are discouraged.
- Nuts: Cashews, pistachios, and Brazil nuts are suggested for avoidance.
- Beverages: The diet also advises A+ individuals to avoid certain beverages like beer, soda, and sparkling water.
The Scientific Consensus: Lack of Evidence
It is crucial to understand that the blood type diet is widely considered a fad diet by the mainstream scientific and medical community. The theory that blood type determines optimal dietary needs is not supported by credible research. Numerous systematic reviews and studies have failed to find a link between blood type and beneficial health outcomes from following the specified diet.
For example, a study published in PLoS ONE in 2014 examined the association between blood type diets and cardiometabolic risk factors. While participants who followed the Type A diet showed improved health markers, these benefits were observed across all blood types, not just Type A individuals. This indicates that the positive effects were likely due to eating healthier, whole foods and not the specific blood type theory.
The diet's claims about lectins—proteins in plants that can cause cell clumping—are also largely unfounded. Most lectins react with all blood types, and cooking effectively destroys these proteins, neutralizing their potential effect.
Blood Type Diet vs. Evidence-Based Nutrition
| Feature | Blood Type Diet for A+ | Evidence-Based Nutrition |
|---|---|---|
| Focus | Eliminating specific foods based on blood type theory. | Emphasizing nutrient-density and overall dietary pattern. |
| Red Meat | Strictly avoid all red meat. | Lean red meat can be part of a balanced diet in moderation. |
| Dairy | Largely avoid most dairy products. | Low-fat or fortified dairy can be an excellent source of calcium. |
| Grains | Restrict wheat and specific grains. | Whole grains are a cornerstone of a heart-healthy diet. |
| Protein Source | Primarily plant-based (tofu, legumes). | Balanced mix of lean protein sources, including plant and animal options. |
| Scientific Basis | Lacks supporting scientific evidence. | Supported by extensive clinical research and data. |
| Potential Pitfall | Unnecessary nutrient restriction and over-reliance on a single, unproven factor. | Focus on overall balance, limiting processed foods for everyone. |
Potential Risks and Considerations
While the blood type diet for A+ emphasizes many healthy foods like fresh produce and legumes, its restrictive nature poses certain risks. Eliminating entire food groups, such as dairy or whole grains, without a valid medical reason can lead to nutritional deficiencies. Dairy products are a key source of calcium and vitamin D, and their unnecessary removal from the diet could impact bone health.
Furthermore, the diet's restrictive nature makes it difficult to sustain in the long term and can foster an unhealthy relationship with food. Instead of focusing on unfounded theories, a consultation with a registered dietitian or healthcare provider can help create a personalized nutrition plan based on a person's actual health status, lifestyle, and dietary needs. Focusing on a balanced diet rich in whole foods, like the Mediterranean or DASH diet, is a proven path to improved health, regardless of blood type.
Conclusion
For individuals with A+ blood, the blood type diet suggests a path of strict avoidance of red meat, most dairy, certain grains, and other specific foods. While this approach aligns with a plant-forward eating style that can be beneficial, the scientific foundation for these specific, blood type-based recommendations is non-existent. Any health improvements experienced are likely the result of a general shift towards a healthier, less-processed diet, not a reaction to blood type-specific foods. Rather than adhering to unproven dietary rules, a more effective and safe strategy is to embrace a balanced and varied diet, seeking advice from healthcare professionals to meet individual nutritional needs.
Read more about the scientific debunking of the blood type diet from WebMD.
