Ask the Doctors

Dear Doctor: Does eating for one's blood type really work? For my own blood type, I am supposed to avoid foods like avocados, bananas, strawberries and many other foods that I would consider healthy choices. I certainly don't want to feel guilty for eating foods that this plan suggests avoiding. What is your take on this?

Dear Reader: You're referring to an eating plan that was popularized by a diet book published in the mid-1990s. The author's premise was that what you eat, as well as the way in which you exercise, should be based on your own particular blood type. For instance, individuals with Type A blood are advised to become vegetarians, substituting plant-based proteins for meat, which the diet refers to as "toxic." The plan also recommends they seek out gentle and calming exercise, such as yoga and tai chi. For those with Type O blood, by contrast, the dietary emphasis is on meats, with advice to limit grains and dairy. Type O individuals are urged to take up vigorous exercise like running, contact sports and martial arts. Those with Types B and AB blood also have personalized diet and exercise guidelines. Each of the eating plans, which also includes vitamins and supplements, is quite specific and even restrictive. The outcome of following the diet, according to claims made by the author, is improved health and a lower risk of disease.

The argument for this dietary approach hinges in part on the differences in blood group antigens, which are markers that are present on the membranes of red blood cells. These antigens will set off an immune response when they encounter foreign antigens. For example, someone with Type A blood cannot receive a transfusion of Type B blood because the antigens in the Type B blood will set off alarms and cause the immune system to go on the attack. Someone with Type AB blood can receive either Type A or B blood but, due to the blood antigens, can safely donate only to someone else with Type AB.

It's true that blood can reveal a lot about a person's overall health. Physicians rely on blood tests to learn a patient's glucose and cholesterol levels, hormone levels, how well the liver, kidneys and vascular system are functioning, whether the body is fighting some type of infection, and whether the signs of certain cancers are present. In addition, it is now generally accepted that specific blood types are associated with a higher risk of certain diseases and conditions, including pancreatic cancer, deep vein blood clots and heart attack associated with coronary artery disease. But whether blood antigens dictate food choices and exercise methods in the ways that this diet lays out remains up for debate. At this time, rigorous studies in peer-reviewed journals are lacking.

Diet is a highly personal choice, and as we all know from the ever-shifting content (and lately, the shape) of the so-called food pyramid, it's not an exact science. In our opinion, as long as you're eating a healthful and balanced diet, you have nothing to feel guilty about.

(Send your questions to, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

More like Ask the Doctors