The concept of blood type diets was originally put forth by the naturopathic physician Dr. Peter J. D’Adamo in his book, “Eat Right 4 Your Type.” He claims that differing blood types evolved at various points in our genetic history and that your blood type should determine what you eat and how you exercise.

Blood type diets are a system of eating which categorize foods as beneficial, neutral, or harmful. It’s based on a person’s blood type and other factors.

D’Adamo claims foods harmful to your blood type cause an agglutination reaction. This makes blood cells stick together, increasing the risk of disease.

Read on to learn more about this diet and D’Adamo’s claims.

The blood type diet requires a regimen called compliance. This refers to eating “beneficials.” Beneficials are chosen for each blood type, based upon the lectins, or molecules, which the food contains.

On this diet, people are defined as being “secretors” or “nonsecretors.” These terms refer to an individual’s ability to secrete blood type antigens into bodily fluids. What you eat is partly based upon your secretor status. This is why the diet is known as an individualized plan.

Food ratios are also provided for each blood type group. These are further broken down into ratios specifically recommended for people of African, Caucasian, and Asian descent. Supplements are recommended for blood type diets, which are sold on D’Adamo’s website.

According to Dr. D’Adamo, the A-positive blood type became prevalent during the early years of the agricultural age. He theorizes this is why people with this blood type can readily digest vegetables and carbohydrates, but have a difficult time digesting animal protein and fat.

The A-positive blood type diet is primarily vegetarian. D’Adamo believes people with this blood type have less-than-robust immune systems and are prone to anxiety. His diet plan promises:

  • weight loss
  • less disease
  • more energy
  • better digestion

As with any diet, people may try this plan in order to lose weight or for other health benefits. Weight loss and lowered cholesterol have been reported by people who have tried this diet. However, there’s no evidence the theory underlying this diet caused these results.

Like many other food plans, this plan stresses avoidance of:

  • processed foods
  • foods high in sugar
  • simple carbohydrates

These diet measures are known to benefit anyone’s health, regardless of blood type.

D’Adamo recommends people on the A-positive blood type diet eat an organic, vegetarian, or almost-vegetarian food plan. Foods to eat include:

  • soy protein, such as tofu
  • certain grains, such as spelt, hulled barley, and sprouted bread
  • walnuts, pumpkin seeds, and peanuts
  • olive oil
  • certain fruits, such as blueberries and elderberries
  • certain kinds of beans and legumes
  • certain vegetables, especially dark, leafy greens, such as kale, Swiss chard, and spinach
  • garlic and onions
  • cold-water fish, such as sardines and salmon
  • limited amounts of chicken and turkey
  • green tea
  • ginger

The diet recommends eating protein at the start of the day. Canned sardines or a smoothie made with silken tofu and goat milk may be a good option.

Limited amounts of animal protein, such as turkey and eggs, are allowed on this diet plan. They may be eaten for breakfast. Vegetables, fruits, and the allowed grains may be eaten at any meal.

The list of foods people with A-positive blood should avoid is extremely extensive. It includes, but isn’t limited to:

  • beef
  • pork
  • lamb
  • cow’s milk
  • potatoes, yams, and sweet potatoes
  • certain vegetables, such as cabbage, eggplant, tomatoes, peppers, and mushrooms
  • lima beans
  • certain fruits, such as melons, oranges, strawberries, and mangos
  • poultry other than chicken and turkey, such as duck
  • venison
  • fish, such as bluefish, barracuda, haddock, herring, and catfish
  • some grains and grain products, such as wheat bran, multigrain bread, and durum wheat
  • refined sugar
  • refined carbohydrates, such as white flour and white bread
  • oils other than olive oil
  • artificial ingredients
  • most condiments

There’s no scientific evidence this diet works or that it alleviates any specific health conditions. Medical conditions which D’Adamo states are associated with this blood type include:

There has been research examining if blood types are at risk of developing certain conditions. A large 2012 study found non-O blood type groups, including type A blood, were associated with a higher risk of coronary heart disease. A 2015 study found the type A blood group had an increased risk of type 2 diabetes. More research is needed to understand why.

One 2014 study found that adherence to the A-positive blood type diet might yield benefits, such as:

  • reduced body mass index (BMI)
  • blood pressure
  • serum triglycerides
  • cholesterol

However, these benefits weren’t seen to be influenced by, or associated with, study participants’ blood types.

While there are no specific health risks associated with this diet, it’s highly restrictive and hard to follow. It’s important that anyone striving to follow this eating plan makes sure they’re getting broad-based nutrition from a wide range of foods, including protein sources.

Blood type diets may yield weight loss and other positive results because they’re highly restrictive. They also eliminate foods which are known to adversely affect health.

However, there’s no scientific evidence linking a person’s blood type to their need to avoid, or eat, specific foods.

If you do decide to follow this plan, make sure to eat as wide a range of foods as possible so you get enough nutrition. You can also talk to your doctor about your individual risk of developing disease. They can help you make lifestyle changes to ensure you’re living your healthiest life.