The Origins of the Blood Type Diet
The idea that one's blood type should dictate dietary choices was popularized by naturopathic doctor Peter D'Adamo in his 1996 book, Eat Right 4 Your Type. The theory is based on two main claims: that blood types evolved with human civilizations, and that certain proteins called lectins, found in foods, react differently with each blood type's antigens. D'Adamo theorized that early hunter-gatherers were type O, so they should eat high-protein diets. As humans adopted agrarian lifestyles, type A emerged, and a vegetarian diet was recommended. Type B, supposedly evolving from nomadic tribes, was suited for a diet rich in dairy. Type AB is considered a modern mix of both.
Blood Type Diet's Recommendations on Dairy
According to the unproven Blood Type Diet theory, dairy recommendations vary significantly by blood group.
Blood Type B and Dairy
Type B individuals are believed to have originated from nomadic tribes with high dairy consumption. The diet suggests that Type B is the only blood type that can fully enjoy and metabolize a wide variety of dairy products without issues, including milk, yogurt, and cheese.
Blood Type AB and Dairy
As a mix of Types A and B, individuals with Type AB blood are advised to consume dairy in moderation. The diet suggests that some dairy products like yogurt and kefir are particularly beneficial for this group.
Blood Type A and Dairy
Based on the agrarian ancestral theory, Type A individuals are advised to limit or completely avoid dairy. The claim is that they have difficulty digesting dairy products, though some sources within the diet's framework make exceptions for fermented dairy like yogurt and kefir.
Blood Type O and Dairy
The 'hunter-gatherer' Type O is encouraged to avoid most dairy and grains. The diet claims these foods can cause digestive and weight gain issues for this blood type.
Scientific Scrutiny of the Blood Type Diet
Despite its popularity, the scientific community has widely dismissed the Blood Type Diet. Multiple large-scale reviews have found no scientific evidence to support the theory that blood type should dictate dietary choices.
- A comprehensive 2013 systematic review of 1,415 references in the American Journal of Clinical Nutrition found no studies validating the diet's claims.
- Researchers at the University of Toronto similarly found no evidence that the Blood Type Diet works, noting that any health improvements are likely due to the diet's general promotion of healthier eating habits, such as reducing processed foods.
- Health professionals cite a lack of scientific rationale, with the theory contradicting fundamental principles of human physiology and digestion.
Individual Dairy Tolerance vs. Blood Type
Instead of blood type, the primary factor determining an individual's ability to consume dairy is their body's production of the enzyme lactase. Lactase is responsible for breaking down lactose, the sugar found in milk. Lactose intolerance is often a matter of genetics, and it can vary greatly by individual and ethnicity, completely independent of blood type.
Key factors affecting dairy tolerance include:
- Genetics: The C/T 13910 polymorphism is a significant genetic factor associated with lactase persistence or deficiency.
- Gut Microbiome: The balance of bacteria in the gut can influence how well dairy is digested.
- Age: Lactase production naturally declines with age in many people, leading to adult-onset lactose intolerance.
- Health Conditions: Intestinal injuries or conditions can temporarily or permanently reduce lactase production.
Comparing Blood Type Diet to Evidence-Based Nutrition
| Feature | Blood Type Diet (Unproven) | Scientific Consensus (Evidence-Based) |
|---|---|---|
| Basis | Blood type, ancestral evolution, and lectin theory. | Nutrient needs, genetics, and individual tolerance. |
| Type B Dairy | Promotes full consumption of dairy. | No correlation. Tolerance varies by individual lactase production. |
| Type A Dairy | Discourages dairy consumption. | No correlation. Tolerance varies by individual lactase production. |
| Type O Dairy | Discourages most dairy consumption. | No correlation. Tolerance varies by individual lactase production. |
| Type AB Dairy | Moderates dairy consumption. | No correlation. Tolerance varies by individual lactase production. |
| Overall Health | Claims to optimize health and prevent disease. | Focuses on a balanced diet of fruits, vegetables, whole grains, and lean proteins, regardless of blood type. |
The Health Benefits of Dairy (for those who tolerate it)
For individuals without lactose intolerance or a dairy allergy, dairy products offer significant nutritional benefits.
- Rich in Calcium and Vitamin D: Essential for building and maintaining strong bones.
- High-Quality Protein: Crucial for muscle repair and growth.
- Contains a Range of Other Nutrients: Including potassium, phosphorus, and B vitamins.
Conclusion: Listen to Your Body, Not Your Blood Type
While the Blood Type Diet offers a compelling narrative, it lacks scientific validation. The question of what blood type should eat dairy is based on a debunked theory. An individual's ability to tolerate and benefit from dairy is determined by their unique biology, most notably their genetic predisposition to produce the lactase enzyme. The most effective approach to diet is based on established nutritional science, listening to your body's specific responses, and consulting with a healthcare professional to create a balanced diet plan that meets your individual needs. For further reading on the lack of evidence for blood type diets, visit the National Institutes of Health(https://pubmed.ncbi.nlm.nih.gov/23697707/).
