Many medical professionals dispute the theory of a link between food, blood type and health, but the idea of a blood-type diet was popularized in the 1996 book "Eat Right 4 Your Type." In it, naturopathic physician Peter D'Adamo argued that by eating foods most compatible with your blood type, you can lose weight, lessen chronic health conditions and help avoid certain diseases. The book lists foods that are good and bad for each of the four major blood types.
There are four major types of blood—O, A, B and AB. Each of these types is further divided into positive or negative types. Your basic blood type is based on the presence or absence of antigens on the surface of red blood cells. These antigens—A and B--are substances that can trigger an immune response if they're foreign to the body. Your Rh factor, whether your blood is positive or negative, is determined by a third antigen. D'Adamo says Rh factor isn't significant in determining your diet plan. However, he says the antigens that determine your basic blood type have an effect on how you digest your food.
Type A Diet
If you have A-positive or A-negative blood, you follow the diet for type As on the blood type diet. D'Adamo says people with type A blood should follow a mostly vegetarian diet, because on the evolutionary scale, type A blood appeared about the time early man was moving to a more settled, agrarian lifestyle and eating a plant-based diet. D'Adamo says today's type-A individuals are predisposed to heart disease, cancer and diabetes, so following a vegetarian diet with foods that are "fresh, pure and organic" is critical for their sensitive immune systems.
Foods to Avoid
D'Adamo says people of every blood type should avoid processed foods, but Type As have a number of other foods to avoid, too. He recommends people with type-A blood avoid meat, poultry, eggs and dairy products. If you like fish, it should be consumed in only limited amounts. Instead, D'Adamo recommends a diet high in vegetables, fruits, grains, beans, legumes, nuts and seeds. Along with the diet, D'Adamo suggests type As engage in calming exercises, such as yoga and tai chi.
Although the blood type diet is not necessarily intended as a weight-loss plan, it is possible to lose weight by following the type A diet. However, some medical professionals cite a lack of scientific evidence proving this diet plan is any more effective than many others when it comes to weight loss. By cutting out high-calorie and high-fat foods, it's possible to lose some weight initially. The problem for some people is sticking with a restrictive diet over time. There's also a concern you can lose out on important vitamins and minerals when whole food groups are eliminated from the diet.