The Blood Type Diet argues that people with blood type A should eat a vegetarian diet. However, the theory that diet should be determined by blood type is currently unsupported by scientific evidence. Everyone, no matter his blood type, needs to consume sufficient dietary protein.
Blood Type Diet and Protein
According to the Blood Type Diet, since blood type A developed in an agrarian culture, present-day people with blood type A should also eat a vegetarian diet. This may lead to questions about whether type As who were not previously vegetarians can continue to get enough protein in their diets. However, New York University's Langone Medical Center points out that that no clinical studies support the blood type approach to diet planning, and that there is no scientific evidence that blood type determines protein needs.
Protein is present in all tissues, from skin to muscles and organs, and is necessary to the body's processes of repair, regeneration, growth and development. A complete dietary protein contains all nine of the essential amino acids that will be broken down to form proteins in the body. Complete proteins are only found in animal products and soybeans. Most vegetables and grains are incomplete proteins and need to be combined properly to make sure the body's needs are met.
Protein Sources for Vegetarians
Because most plant sources of protein are incomplete, people of any blood type following a vegetarian diet need to be careful to eat many types of protein-rich foods. Vegetarians who eat dairy products and eggs -- or lacto-ovo vegetarians -- can get complete proteins from those sources. Protein is also available in meat substitutes; soybeans and soy products like tofu, tempeh and seitan; and beans, legumes, nuts and whole grains. Eating a wide variety is key to providing the entire range of amino acids necessary for conversion to protein in the body. For example, rice and beans make a complete protein when combined.
Other Protein-Rich Foods
Animal products are the most complete sources of dietary protein. Lean red meats, fish and poultry are all rich in protein, as are eggs, yogurt and dairy products like cheese. The University of Maryland Medical Center recommends that adults consume two to three servings of dietary protein per day. A serving consists of 2 to 3 oz. of meat or fish; one-half cup of cooked dried beans served with brown rice; an egg; or 1 oz. of cheese. Most balanced diets provide enough protein, so protein supplements are rarely necessary.