The Blood Type Diet is based on the theory that each blood type -- O, A, B and AB -- has a specific ability to digest proteins. Eating foods that your body can easily metabolize can keep you healthy. According to Dr. Peter D'Adamo's "Eat Right 4 Your Type," the diet can help you avoid the certain illnesses to which each blood type is prone. The easier digestion is, the more nutrients you can absorb from the foods you eat.
Lectins and Antigens
Lectins are a type of protein found in food; antigens are substances your body isn't able to process that can negatively affect you. According to the Blood Type Diet, each blood type has antigen markers for specific lectins -- proteins that your body doesn't recognize and which can cause health problems. Your antigens are related to your blood type. Foods are categorized as either beneficial, neutral or harmful, based on the interaction of lectins and antigens.
Digestion begins in your mouth with the physical act of chewing and the chemical breakdown of food by enzymes in your saliva. The Blood Type diet says that different blood types have different amounts of these digestive enzymes. For example, type O has the strongest digestive enzymes and the most stomach acid; so people with blood type O do well with high-protein diets, especially diets high in animal protein. People with type A are best-suited to a vegetarian lifestyle and lack the digestive ability to metabolize large quantities of meat.
Digestion and Evolution
Blood types evolved at different points during history. The Blood Type diet theorizes that the best diet for you is the diet common to the time when your blood type developed. Type O is the oldest and best-suited for meat-eating because of the typical hunter/gatherer diet. Type A evolved during the agricultural age and shifts from a meat-based diet to a plant-based diet; therefore people with blood type A do well on vegetarian diets. Next, type B developed as people started migrating -- nomadic peoples who do well with dairy, animal and plant foods. The newest blood type is AB, which came into existence just 1,000 years ago and is still quite rare -- less than 5 percent of the population has AB blood. But for those that do, a combination of foods suitable for both A and B blood types works best.
There is little hard science to back up these theories concerning blood type, diet and digestion. Juliette Kellow, B.Sc., R.D. says, "Medical experts universally agree that the theory is nonsense, and say there is absolutely no link between our blood group and the diet we eat." In addition, because entire food groups are eliminated for certain blood types -- Type O is told not to eat grains, beans or legumes -- nutritional deficiencies are possible. Although you may lose weight eating for your type, pounds lost are most likely due to the restrictive nature of the diet and not from the reaction of antigens and lectins.