The Blood Type Diet Explained
When Eat Right 4 Your Type hit bookstore shelves in 1996, it gained immediate popularity, shooting to the top of several bestseller lists, and over time selling millions of copies. It is still hugely popular today. The diet plan outlined in the book by naturopathic physician Peter D'Adamo, M.D., is based on the premise that a person's blood type — whether A, B, AB, or O — influences weight gain and health, through the ability to effectively metabolize different foods. Because of that, nutritional recommendations are made based solely on blood type.
Coming at a time when most mainstream diet plans still adopted a 'one-size-fits-all' approach, the idea of tailoring the diet to the individual piqued a lot of interest. For example, the diet recommends type A individuals eat a mostly vegetarian diet full of fruits and vegetables, whole grains, and legumes, while the type O diet is protein-heavy, emphasizing lean meats and vegetables. The diets for B and AB blood types are somewhere in between. There are also unique recommendations for vitamin supplements and even exercise, which again are tailored to the specific blood type (via WebMD).
The Blood Type diet emphasizes whole foods
Despite the diet's huge popularity and a mountain of anecdotal evidence, researchers are quick to point out that the scientific evidence in support of the blood-type diet is weak. A major 2013 review of over a thousand studies, published in the American Journal of Clinical Nutrition, found little to support the book's claims. And Nancy Rahnama, M.D., a board-certified bariatric physician, summarized the view of many medical professionals when she said, "There is no explanation to support a link between an individual's blood type and their interactions with certain foods and weight" (via Prevention). That being said, each of the studies that purported to study the eating based on blood type, had serious design flaws, so better research should be done before drawing firm conclusions (via Healthline).
Dr. D'Adamo's diet recommendations, for each of the blood types, focuses largely on whole, unprocessed, nutrient-dense foods, and researchers suspect that health improvements may be due more to a general improvement in diet than to a specific food/blood type connection. Dr. Rahnama adds "Despite the lack of evidence to support the Blood Type Diet, many do feel better when attempting this restricted plan because it promotes a cleaner diet devoid of junk food, processed food, and sugar."
You can always talk to your doctor to learn about eating styles that may be right for you and your health goals. Science-wise, there isn't a whole lot to support the Blood Type Diet, but if you feel like it's working for you, there's no sense in changing things up.