Q: I am a resident in a retirement home. One of the other residents is trying to influence people to switch to the “blood-type diet.” Is there any information you can send me or refer me to which I can use to inform people of the scientific status of that approach?
Answer : According to Susan B. Roberts, PhD, director of Tufts’ HNRCA Energy Metabolism Laboratory and author of The “I” Diet www.myidiet.com, “There is really nothing scientifically supporting this idea.” She points to a recent systematic review of the scientific evidence published in the American Journal of Clinical Nutrition, which concluded bluntly, “No evidence currently exists to validate the purported health benefits of blood-type diets.”
The theory behind “blood-type diets” is based on the idea that your A-B-O blood type influences how particular dietary patterns affect your health. As promulgated by naturopath and author Peter J. D’Amado, proteins in foods called lectins are said to be responsible for many ailments; people with different blood types, the theory goes, respond differently to different lectins. For example, the 10% of the population with type B blood can supposedly eat the most varied diet, including dairy products.
To scientifically test this theory, you would need to answer this question: In humans grouped according to blood type, does adherence to a specific diet improve health and/or decrease risk of disease compared with nonadherence to the diet? For the recent analysis, reviewers screened 1,415 references in the medical literature and found only one study addressing variation by blood type, which nonetheless did not answer the key question. Other researchers have identified a handful of weak associations between blood type and disease risk—far less than would be expected if this theory were true.