The blood type diet is based on your blood type. If your blood type is A, you should eat vegetarian foods, if it is type O, you should eat mostly meat and not eat grains, and if it is type B, you can eat many types of food, such as dairy, which you cannot eat for type A and O.

This weight loss plan was made by Dr. Peter D’Adamo, a naturopathic doctor. He thinks that eating foods that are right for your blood type will make you feel better. He also thinks you will be less likely to store the food away as fat and less likely to have some health problems.

Dr. D’Adamo thinks blood type is an evolutionary marker that points to which foods are best for your body and which foods can harm it. He thinks that we should be eating what our ancestors with the same blood type ate. He says type Os were meat-eating hunter-gatherers, while type As were vegetarian farmers, and type Bs were nomads, eating many more types of food.

Dr. D’Adamo advises that all people eat mostly fresh, natural foods, and cut out processed foods. Chocolate, coffee, and alcohol should not be eaten. Dr. D’Adamo also gives exercise advice. Here are the eating plans:

Blood TypeFoods That Can Be EatenFoods That Should Not Be EatenExercise

Type A

Veggies, fruit, grains, beans, legumes, nuts, and seedsDairy, meat, fish, poultry, eggs, and processed foodsCalming exercise like golf or yoga

Type B

Veggies, fruit, grains, beans, legumes, meat, poultry, fish, eggs, and dairyNuts, seeds, and processed foodsModerate intensity exercise like walking, hiking, and tennis

Type AB

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

Type O

Meat, poultry, fish, and olive oil; limit: certain veggies, nuts, seeds, and eggsDairy, grains like cereal, bread, pasta, and rice; beans, and processed foodsVigorous exercise like running

This weight loss plan is not supported by evidence.

The type A and O diets are very strict. They remove whole groups of food. This is an easy way to cut down on calories and will lead to some weight loss. But you are also taking out vitamins, minerals, and other nutrients that you need.

Dr. D’Adamo advises specific supplements for each blood type to make sure you meet all your nutrient needs. Supplements can give you a little extra nutrition, but they should not be used as a substitute for a well balanced diet. Dr. D’Adamo encourages dieters to buy from his own line of supplements that were made to go with his weight loss plans.

You should not try this weight loss plan. It greatly limits the food you can eat. This makes it hard to meet nutrient needs and follow the plan for a long time. People who want to lose weight should choose a weight loss plan that is backed by evidence and matches their lifestyle.