What is the “Blood Type Diet?”

dietThere will always be a hunger for diet books. Hope reigns eternal when it comes to the quest for shedding those extra pounds. No matter how many failed diets the overweight have struggled through, there is always the hope that maybe the next one will produce the sought-after miracle. And the more scientific sounding a diet is, the more seductive its allure. Pseudoscience cloaked in legitimate scientific terms seems to work particularly well. Take Peter D’Adamo’s epic Eat Right 4 Your Blood Type. Sometimes you can quickly look through a book and find a claim that immediately casts a shadow on the whole work. D’Adamo makes the statement that people with type O blood are more prone to suffer from hypothyroidism because their bodies tend not to produce enough iodine. The remedy? Type Os should eat meat and avoid wheat. This is absurd beyond belief. The body does not produce iodine, no matter what blood type is involved. It is a mineral that has to be furnished by the diet. And in any case, meat is not a good source. Should we be surprised that D’Adamo has such a poor grasp of nutrition? Probably not. He’s not a nutritional scientist. He’s a naturopath. The rest of the “science” in the Blood Type approach to diet is hard to encapsulate because it is so bizarre and confusing. He points out, correctly, that blood type is determined by the presence or absence of two proteins on the surface of red blood cells and then goes on to describe how these can interact with food components and cause disease and weight problems.

The culprits in food are proteins called lectins. According to D’Adamo these can interact with the proteins on red blood cells and cause these cells to clump together and gum up the body’s internal machinery. What evidence is there for this? Essentially none. Take a drop of blood, put it under a microscope and add lectins and there may be an effect. But this is very different from anything that happens in the body. Lectins do not survive digestion and do not enter the bloodstream in an unaltered form. If they did, there could be dire consequences. In fact, D’Adamo tries to make a point of this by referring to Georgi Markov, the Bulgarian émigré who was poisoned in London by the Bulgarian secret police using ricin, extracted from castor beans. Ricin is indeed a lectin. But this celebrated assassination was carried out by injecting the chemical directly into the victim’s bloodstream using a specially made umbrella. Feeding him the ricin would not have done it! The theory behind the Blood Type Diet makes no sense. But that does not necessarily mean the diet doesn’t work. That can only be determined by appropriate experiments. D’Adamo does furnish us with any such. Where is the evidence for the wild ramblings about agglutinated red blood cells after eating the wrong kinds of foods? How come physicians have not noted organ failure in people consuming diets inappropriate for their blood type? After all, most of us do not follow D’Adamo’s advice. Where are the documented trials about people who have lost weight? The bottom line is that there is no evidence for these silly meanderings and confusing people with such nonsense will not put them on the path for proper nutrition.

Joe Schwarcz

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