Blood Type Diet
The theory states there are good foods for each blood type. The types are the result of our evolution, in Africa type O was predominant, which is the hunter-gatherer type, then the migration to colder climates created the nomadic B, settled life in villages, farms created the A. The last one to arrive is AB which is a mix of both A and B.
On top of the main types, there is the secretor status. In the genetics of the secretor system two options exist. A person can be either a Secretor or a Non-secretor. This is completely independent of whether you are a blood type A, B, AB, or O. This means that someone can be an A Secretor or an A Non-secretor, a B Secretor or a B Non-secretor etc.
There are lab tests to determine this status. Some clues, being a Non-secretor offers a slight increase risk for having a problem with habitual snoring. Non-secretors tend to have more digestive problems. The easiest way to handle this one is if a food item has AVOID for either _S or _NS for the same type, to avoid it, to be on the safe side.