Ask Marilyn – Star Question: The blood type diet?
Q: I have heard that some foods are good to eat if they are related to your blood group. For example I am A positive and it is said that I should not eat too many Brazil nuts as my system does not agree with them nor oranges… Do you agree with this form of belief? That some food should be eaten according to your blood group?
A: The blood type diet was introduced by Peter D’Adamo who suggested that because the cells in our bodies have certain distinct chains of polysaccharides which put us into one of four blood types, O, A, AB or B then we should eat a diet that is right for whichever blood type we are.
The blood type theory is founded on anthropology because it is reasoned that as type O was the first blood type to evolve, then people with this blood type should eat like our hunter-gatherer ancestors. The theory is based on the action of lectins, which are proteins found on the surface of certain foods. So when you eat a food containing lectins that are not compatible with your blood type then the lectins can cause health problems.
I have a problem with the thinking that we can all just be slotted into four groups, according to the four blood types. And in fact there are more than four because with each group there are sub-groups (e.g. rhesus positive and negative) and these differences are not taken into account. The other major problem is the lack of evidence. There has not been any scientific evidence to show that an interaction between blood type and diet has an impact on health. Biochemical research has also found no differences in how lectins react with each different blood type. Even D’Adamo adds a warning to say that even within each blood type there are individual variations so don’t expect all the recommendations to apply to you. The difficulty would then be knowing which ones apply and which ones don’t and then the blood typing theory starts to fall down.