Back in the mid 90’s a book was written by Peter D’Adamo advocating that your diet should be different depending on your blood type. It also claimed that if you ate the wrong food for your blood type, you would not be well. An interesting premise. The question arises, is there any evidence for this claim?
This interest by D’Adamo came about through his father’s work. His father James noticed that different diets affected people differently at the European health spas he was working at. So with his “keen powers of deduction and insight” he asked himself the question what nourishes the body, and his answer was blood (whether this is true or not shall be looked at later). So his conclusion was that people with different blood types should eat differently. He based his work initially by only looking at the ABO grouping. Eventually he published a book about diet named after himself and set up an institute. As a side note, it’s interesting that this institute also practices cranial manipulation, spinal manipulation, and structural alignment. He claims that some of these practices can solve emotional and mental problems, but that can wait for another post.
So Peter jumps on his fathers idea about blood type and diet, and begins to search for evidence. He finds two studies which he thinks vindicate his father. The first one is a study about peptic ulcers and the second about stomach cancers. Now from the text it is hard to pinpoint exactly the studies he is refering to, but looking in the index it looks like these studies are both by
E. Aird et al., both published in 1954. One is called "The Blood Groups in Relation to Peptic Ulceration and Carcinoma of Colon, Rectum, Breast, and Bronchus". You can read the paper here. This is enough to convince him his father is correct.
Now, this in the 1980's. Why doesn't he search for more recent data? Why rely on only two studies? I shall ignore those crucial questions and look at the above study. Its results say that in the British hospitals where they gathered their data, blood type A was more common in patients suffering from cancer of the stomach, and O-type was more common in patients suffering from peptic ulcers. Notice that there is no mention of diet in the study. Nowhere is there a claim that diet is causing the stomach cancer or ulcer. That is a huge leap to make. But that's not all. I hope he kept reading the paper because here is an interesting extract from the comment section:
"The simplest, though not necessarily the most acceptable, explanation of ouir findings would be the assumption that A substance is carcinogenic with respect to the stomach while both A substance and B substance protect against peptic ulcer."
So there is another possibility about why the difference. Maybe it's inherent in your genes. There is no way diet can affect that.
Now firstly we should really do other studies to see if this finding holds true for other groups of patients. You should never rely on just one study. So has any other studies been done? How about this one by Akumabor, "The ABO blood groups in relation to carcinoma of the stomach and duodenal ulcer in a Nigerian community" published in, wait for it, 1986. Why didn't he use this one? It was while he was researching his book. It was published way before his book was released. Maybe because of this conclusion:
"Contrary to expectations, carcinoma of the stomach in this community predominates in group O persons, occurring in 64·2%, whereas blood group O occurs in only 55·6% of the population. This is in contrast with previous studies in which carcinoma of the stomach was commonest in blood group A patients."
So in this study, it O types are more common with stomach cancers. This negates the data his beliefs are founded on. Maybe if lots of data from all around the world was taken, all these blood type differences would cancel each other out and there would be no relationship between blood type and stomach cancers. There goes one of his main reasons for believing what he does.
But what about peptic ulcers? Could there be reasons other than blood type and diet? Stress and stomach acid were common reasons people thought why ulcers may be induced. And there was this Australian named Robin Warren who claimed that is was a bacteria that caused ulcers of the stomach. Initial people thought he was ga-ga, but as the evidence mounted up and mounted up and mounted up, the doubters changed thier minds and agreed that he was right. His reward, the 2005 Nobel Prize. It is now know that bacteria is the main cause of ulcers.
So where does this leave D'Adamo? Firstly, he should have based his ideas on more than a couple of studies. He should have looked for evidence that contradicted his theory. Good research involves trying to find holes in your own theory. Your theory and the evidence supporting it has to be watertight if you wish it to be accepted.
That's quite a long post and it's just about the introduction. He's not off to a good start. But let's ignore all of this as I'll look into why he thinks blood type and diet are interlinked in my next post.