Myth: You should eat according to your blood type.
Fact: Your blood group has nothing to do with your ability to digest food, or what diet best suits you.
Genetic variation between individuals is the reason why some people don’t do as well on certain diets, and why some people don’t respond in the same way to dietary change in scientific studies. This has been known for decades and started the new scientific frontier of nutrigenetics: designing diets and eating plans according to your genetic make-up. Geneticists who work in nutrigenetics say the blood-type diet is silly: it’s the equivalent of reading tea leaves to determine what to have for dinner. This is because there are hundreds of known polymorphisms (genetic variations) that influence diet and health, and none of them relates to blood type. For example, there are polymorphisms (variants) that affect how your LDL or ’bad’ cholesterol responds to eating fat; others affect how homocysteine levels respond to a vegetarian diet lower in vitamin B12.
Who discovered blood types? Austrian Karl Landsteiner discovered blood types in 1901 and this allowed the first safe blood transfusions. He received a Nobel prize for his work in 1930. Blood types A, B, AB and O are distinguished by the different combinations of antigens on the surface of your red blood cells and antibodies in your plasma. For example, blood type A has A antigens on the surface of the red blood cells and B antibodies in the plasma. Somebody with blood group B has B antigens on the surface of their red blood cells and A antibodies in their blood plasma. If you receive the wrong blood type as a transfusion, antigens on the surface of the donor red blood cells will react with the antibodies in your plasma and clump together, impairing circulation and may even kill you.
How blood type relates to the food you should eat is where the creativity comes in: Proponents of blood-type diets say blood type also correlates with a number of characteristics affecting digestion – for example, type O produces more stomach acid and therefore can more easily digest meat, and type As should be vegetarian because they produce less acid. Even if type Os did produce a bit more acid – and this is a very big ‘if ’ – it would make negligible difference to the ability to digest meat. Although acid is a big help, it is protein-digesting enzymes from the pancreas that do all the heavy lifting when it comes to protein digestion. Millions of people take medications to significantly reduce acid production because of acid reflux, yet they can still digest meat.
The bottom line: I can understand the attraction to a diet that claims we fall into distinct ‘types’ which each require a specific dietary approach. It just seems to make sense. But just because it sounds plausible, doesn’t mean it is. There is no scientific foundation to eating according to your blood type. However, if you want to know more about ‘nutrigenetics’, type it into your favourite search engine – and see your own doctor before embarking on any genetic testing.
Nicole Senior is an Accredited Practising Dietitian and Nutritionist and author of Food Myths released on February 1 and available in bookshops and online and from www.greatideas.net.au