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Should you change what you eat if you’re type A or type O? Here’s what you should know about the Blood Type Diet.

Lisa Valente, M.S., RD
February 09, 2021
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Tomato, Cucumber & White-Bean Salad with Basil Vinaigrette

I really loved finding out my blood type when I donated blood (A-, if you're curious). The science around blood types is pretty interesting and fairly new. There's A, AB, B and O and all types can be positive or negative. It wasn't until the early 1900's that we learned about different blood types, since some people were dying from blood transfusions. Then in the 1960's scientists developed RhoGAM, a key drug that helps protect babies born to moms with Rh-negative blood (thank you, science). Research has even found that certain blood types are correlated with certain diseases, like some types of cancer and heart disease. But when it comes to impacting what you eat, does your blood type make a difference? Here's the scoop on the Blood Type Diet, what you're supposed to eat depending on your blood type and if it actually works. 

What is the Blood Type Diet? 

The Blood Type Diet is based on the book Eat Right 4 Your Type by Dr. Peter J. D'Adamo. He is a naturopathic physician. The book is a New York Times bestseller and claims to help people find the right foods, vitamins and minerals to eat based on your blood type for optimal health and weight. The book goes through a bit of a history of blood types before applying theories to how and what you should eat and exercise based on your blood type. (These Are the 5 Best Exercises for Your Health, According to a Harvard Doctor.)

What can you eat on the Blood Type Diet? 

The Blood Type Diet says there are different rules for eating based on your blood type. Here's the gist of how each blood type shakes out, according to the book. 

Blood type O: Eat a high-protein, low-carb diet with meat. Cut out most grains and wheat. Do vigorous exercise. Type O should choose lots of meat, fish, vegetables and fruit but limit grains and legumes. Avoid dairy and wheat. 

Blood type A: Eat a vegetarian high-carb, low-fat diet. Do gentle exercise. Type A should consume lots of fruit and vegetables as well as seafood and plant-based proteins, like tofu, but should avoid red meat. 

Blood type B: The only blood type that should eat dairy. Consume a variety of foods, including meat. Do moderate exercise. This diverse diet should include meat, dairy, fruits, vegetables and grains.

Blood type AB: A mix of A and B diets. Should do calming exercises. Consume fruits, vegetables, tofu, lamb and fish.

What does the science say?

There isn't research that says eating for your blood type makes you any healthier or helps you lose wight. For some people, a diet that falls into one of these buckets may work for them, but for many—these diets are unnecessarily restrictive. I actually eat somewhat similarly to what's recommended for my blood type, type A, since I love carbs and eat lots of plants, but I think that happens to be a coincidence. I also like more high-intensity exercise, like spinning and running, and definitely include plenty of heart-healthy fats in my diet. For what it's worth, my husband loves meat and we happen to share a blood type. 

Eating a majority plant-based diet (type A) or a lower-carb, higher-protein diet (type O) might help you lose weight at first. If you switch from a highly-processed diet with lots of added sugar, to a more whole-foods based diet—you'll probably feel a little better and may have more energy. But it's random to base these choices on your blood type. I'm all for trying to get more vegetables in your diet, regardless of your blood type. At first glance, all of the blood types should eat more fruits and vegetables. But getting into the weeds, these foods get much more random. Type A should avoid kidney beans for weight loss and type B should skip chicken and corn to lose weight. That just doesn't make any sense. 

The book brings up lectins as being important based on your blood type. Lectins are also often talked about by Paleo and Whole30 proponents. Lectins are an antinutrient, found in many plant foods, including beans and vegetables. Most of the lectins we eat are cooked (or soaked or fermented), which deactivates the protein therefore reducing any downside in the body, regardless of your blood type. (Here's what you should know about lectins and the anti-lectin diet.) Plus, foods like beans and whole grains that contain lectins also have plenty of good-for-you nutrients like fiber, vitamins and minerals. 

D'Adamo also talks about the importance of individual diets. That's one place where we agree, as everyone is going to have a very unique, ideal way of eating based on genetics, lifestyle and preferences. Unfortunately, eating based on your blood type may feel like you're eating a diet designed just for you—but this isn't personalized nutrition.

I also don't love that in the book, he's basically saying if you don't do what he says you're going to increase your risk for diseases like cancer, heart disease and inflammation. Yes, your diet can help reduce your risk of those diseases but a lot of chronic disease risk is based on factors outside of our control, such as genetics and socioeconomic factors. Eating antioxidant-rich fruits, vegetables, whole grains, healthy proteins and fats plus exercising and reducing stress in your life can help too. I don't think it's necessary to shame and blame people into eating a certain way, especially one that isn't proven to help (but may help you sell books). 

I truly believe everyone should be eating in a way that helps them feel good. It's possible that foods you love might align with what your blood type recommends. Type O and type A are the most common blood types by far, and at first glance, those two diets don't seem that far fetched. Eating a higher-protein diet (type O) or a plant-based diet (type A) might work for you. But there's no need to change your diet for your blood type, and definitely no need to go as specific as eliminating certain types of beans from your diet. In the meantime, donate blood and save a life (and learn your blood type if you don't know it yet). 

Welcome to The Beet. A weekly column where nutrition editor and registered dietitian Lisa Valente tackles buzzy nutrition topics and tells you what you need to know, with science and a little bit of sass.