The blood type diet, as its name suggests, is a diet based on your blood type. According to this diet, if your blood type is A, you should eat a mainly vegetarian diet, if it’s type O, you should eat mostly meat and avoid grains, and if it’s type B, you are in luck—you can eat a variety of food, including dairy, which is excluded for type As and Os.

How Is This Diet Supposed to Work?

Developed by Dr. Peter D’Adamo, a naturopathic physician, the premise of this diet is that by eating foods that are right for your blood type, you will feel better, be less likely to store the food as fat, and be less likely to develop certain diseases and cancers.

According to Dr. D’Adamo, your blood type is an evolutionary marker that indicates which foods are best suited for your body and which foods can be harmful. He believes that we should be eating what our ancestors with the same blood type did. For example type Os were apparently meat-eating hunter-gatherers, while type As were vegetarian farmers, and type Bs were nomads, eating a more varied diet.

What’s Involved?

Dr. D’Adamo recommends that everyone eat mostly fresh, natural foods, and cut out processed foods. Modern day indulgences such as chocolate, coffee, and alcohol should also be limited or avoided according to Dr. D’Adamo. But this is where most of the commonalities between different blood types end. In addition, Dr. D’Adamo also provides exercise recommendations. Here is a summary of the different eating plans on this diet:

Blood TypeFoods AllowedFoods to AvoidExercise

Type A

Vegetables, fruit, grains, beans, legumes, nuts, and seedsDairy, meat, fish, poultry, eggs, and processed foodsCalming exercise (eg, golf or yoga)

Type B

Vegetables, fruit, grains, beans, legumes, meat, poultry, fish, eggs, and dairyNuts, seeds, and processed foodsModerate intensity exercise (eg, walking, hiking, and tennis)

Type AB

Foods allowed on both the Type A and Type B diets are all okay, but following a vegan diet most of the time is recommendedProcessed foodsBoth calming and moderate intensity exercise

Type O

Meat, poultry, fish, and olive oil; in moderation: certain vegetables, nuts, seeds, and eggsDairy, grains (eg, cereal, bread, pasta, rice), beans, and processed foodsVigorous exercise (eg, running)

What Does the Research Say?

The theory that our blood type determines what we should eat or what kind of exercise we should do is not supported by scientific evidence.

Are There Any Concerns With This Diet?

The type A and O diets are extremely restricting, eliminating whole groups of food. Doing this is an easy way to cut down on calories and is, therefore, likely to lead to some initial weight loss. But in addition to eliminating calories, you are also eliminating vitamins, minerals, and other vital nutrients.

In fact, Dr. D’Adamo recommends specific supplements for each blood type to make sure you meet all your nutrient needs. The problem is—while supplements can sometimes provide a little extra nutritional insurance, a well-balanced diet should not require supplementation. Moreover, Dr. D’Adamo encourages dieters to buy from his own line of supplements, specifically created to go with his diet plans.

Bottom Line

Although the blood type diet sounds novel and intriguing, it is not recommended. In addition to not being based on solid science, this diet severely restricts the food you can eat. This makes it tough to meet nutrient needs and difficult to follow in the long-term. If you are looking to lose weight, choose a sensible diet plan that is supported by scientific evidence and matches your personality and lifestyle.