Blood Type™ Diet was originally suggested by Peter D'Adamo in his book, "Eat Right For Your Blood Type." The book claims that there are certain foods people should and shouldn't eat according to their blood type.

According to Dr. D'Adamo, "Your blood type has everything to do with how you digest food, your ability to respond to stress, your mental state, the efficiency of your metabolism, and the strength of your immune system."

Dr. D'Adamo's ideas are rooted in evolutionary history. He observed that different blood types (Type O, Type A, Type B, and Type AB) emerged as the environmental conditions and eating styles of our ancestors changed.

For example:

Between 50,000 BC and 25,000 BC - All humans shared the same blood type-Type O. These early humans were skilled hunters, and thrived on a meat-based diet. As a result, the theory goes, people today with type "O" blood.

Between 25,000 BC and 15,000 BC - The world population adapted a more agrarian lifestyle. During this period, Type A blood type emerged as a result to adapt to the new challenges. So, according to Dr. D'Adamo, modern-day "A" and "A-B" blood types are

Climatic changes in the western Himalayan mountains led to the appearance of Type B blood type. It is a balance of both "O" and "A", says D'Adamo. A person with type "B" blood can't burn the fat in red meat as efficiently as a type "O" can. Likewise, a type "B" person doesn't burn carbohydrates as fast as a type "A" does.

Modern civilization: The blending of Type A and Type B blood types resulted in the appearance of the Type AB blood type.

Dr. D'Adamo has studied the physiological effects of substances called lectins. Lectins are proteins found in many commonly eaten foods, particularly the seeds of leguminous plants. They can be absorbed intact from the digestive tract into the bloodstream.

According to Dr. D'Adamo, certain lectins are incompatible with certain blood types. This incompatibility causes the lectin to attract and clump red blood cells. He calls this process agglutination.

According to Dr. D'Adamo, lectin-caused agglutination is the primary cause of many common health complaints. He has tested most common foods for blood-type reactions. Based on this study, he developed a food list that allow people to avoid eating foods containing lectins that are incompatible with their blood type.

The Blood Type Diet divides foods into 16 categories:

Meats and poultry
Seafood
Dairy and eggs
Oils and fats
Nuts and seeds
Beans and legumes
Cereals
Breads and muffins
Grains and pasta
Vegetables
Fruit
Juices and fluids
Spices
Condiments
Herbal teas
Miscellaneous beverages

Foods in these categories are then labeled as "highly beneficial," "neutral," or "avoid" according to each of the four blood types.

Here is a summary of recommendations for various blood types by Dr. D'Adamo:

Type O:

· Emphasize animal proteins 
· Focus on anger management 
· Engage in aerobic exercise to reduce stress 
· Control Type O impulsive behavior 
· As you age, vigorous exercise is crucial

Type A:

· Emphasize vegetables 
· Concentrate on stress management 
· Engage in yoga or gentle exercise to reduce stress 
· Take naps or frequent breaks to stay focused 
· As you age, a regular sleep cycle is crucial to keep your health in balance

Type B:

· Vary your diet 
· Focus on creative outlets 
· Engage in walking and meditation to reduce stress 
· Avoid emotional overreaction 
· Mental activities are crucial to retaining memory as you age

Type AB:

· Eat smaller, more frequent meals 
· Focus on cultivating your natural spiritual tendencies 
· Break up your day with physical activity to feel more energized 
· Avoid feelings of isolation 
· Be aware of your environment as you age, to avoid susceptibility to bacterial infections

Pro

Many people follow this diet to improve their overall level of health. Although weight management is not the focus of the diet, Dr. D'Adamo believes that weight loss is a natural consequence of following a diet tailored to your blood type.

Con

This plan is unrealistic if members of one family have different blood types, causing them to each follow a completely different diet. Each plan unnecessarily eliminates specific groups of foods, which can result in nutrient deficiency.

Some physicians and nutritionists argue that Dr. D'Adamo's theory about lectins lacks solid scientific support. These critics point out that the research that has been done on lectins has been performed mostly in test tubes. Therefore, it is not yet known what, if any, physiological effects lectins have in humans.

Furthermore, many food lectins are destroyed by cooking and/or digestive enzymes, so many critics argue that the number of lectins absorbed intact through the digestive system is minimal.

Other critics point out that Dr. D'Adamo's emphasis on the ABO blood-typing system is somewhat arbitrary. It is only one of many different blood-typing methods, and to date, more than 30 unique markers have been identified on the surface of red blood cells.

The literature finds very small differences in heart disease rates and other diseases from one blood type to another. The Framingham Heart Study found no significant difference between the incidence of heart disease and blood type.

Opponents caution that people with Type O blood may increase their risk of heart disease by adhering to Dr. D'Adamo's Type O diet recommendations.

Critics say that this diet is really a calorie-restricted diet. As with any other low calorie diet, weight loss is likely to occur so long you follow the diet with restricted calories.