A newly released article in the American Journal of Clinical Nutrition examines the validity of blood type diets. This scientific review of existing research concludes “No evidence currently exists to validate the purported health benefits of blood type diets.”
The premise behind blood type diets is that each major blood type (O, A, B, AB) is somehow linked to a set of nutritional needs. The most renowned blood type diet is presented in the book EAT RIGHT 4 YOUR TYPE, by Dr.
Peter D’Adamo, who suggests that your “blood type is the key to your biochemical uniqueness. When you eat right for your type, your body responds the way nature intended.” He presents the assumption that all people with a given blood type (A, B, AB, or O) have the same nutritional needs. Blood type diets have been around for years but there has never been any good science to support the claims made by authors who created them and profit from books written about them. This is another example of someone speculating what might affect health, creating a hypothesis that turns into an opinion, and then is presented as fact to the unsuspecting public. A true hypothesis must be tested in an objective manner to determine if it is true or not. Without being tested or supported by solid research, it remains just an opinion…which is what the blood type diets are at this point.
Intuitively, blood type diet theories don’t make sense to me because they are based on the idea that a person’s blood type is an indication of their ancestry, and subsequently of the types of foods their blood line has evolved to tolerate best. Aside from lack of good scientific support for this idea, there are 2 primary points that make me question the validity of this theory:
- Especially in North America (and to a good extent in other parts of the world now too) we have such a mixed gene pool from intermarrying among ethnicities and races that the assumption that my dominant blood type matches my dominant digestive, metabolic and/or immune tendencies is a BIG assumption which is likely in error. Those of us with mixed genetic heritage have some dominant traits from one parent and some from another…. and our blood type is only one trait. To my knowledge there is no research to substantiate the theory that “metabolic type” is always linked to a person’s blood type. No one really knows if a person can have mom’s blood type but dad’s “metabolic type.” It’s not been researched or tested. It’s an interesting idea… but not an established fact.
- The whole concept of evolution is based on the fact that organisms ADAPT to their environment – including the ability to utilize available food sources. And while some evolutionary changes may occur over centuries (or longer), adaptive changes are on-going. It’s presumptuous to believe that the metabolic, digestive and even immune systems (related to food sensitivities) have not adapted or evolved since the establishment of blood types. The landscape and available food sources have changed substantially in some areas and people adapted/evolved to survive. Their blood types have not changed, but that does not mean other genetic traits have not evolved. I find it irresponsible to assume that a the ability for the body to utilize carbohydrate, protein and fat could not have evolved independent of blood type.
I will acknowledge that some individuals who follow blood type diets may feel better and improve their health. The problem is that there are many variables that may account for the noted improvements. In some cases it may simply be that the person went from eating a lot of processed foods to eating primarily fresh whole foods. In other cases it may be that a person has a food sensitivity to one or more foods they are avoiding on the new diet, or that they are eating many nutrient dense foods, not skipping meals, etc., etc. My point is that until all the other variables are controlled, we don’t really know for sure WHAT change in an individual’s diet can be credited with observed – subjective or objective – health improvements.
I am always open to be proven wrong by valid research and/or substantial supporting evidence, but until then I cannot with good conscience support claims associated with blood type diets. The EAT RIGHT FOR YOUR TYPE website boasts of celebrity endorsements and drops a few names. I am amused. They are lovely people, but are simply stating opinions usually based on a sample size of one. I think I’ll listen to them for advice on performing arts, but will turn to the research scientists for insights on genetics, nutrition, and metabolism. I’m kind of particular as to who I label as experts.
