It is very important if you are following the blood type diet.
It may or not make a difference if a person chooses to follow the GenoType diet.
If you are following SWAMI for most it only shifts a few foods, but for some people it can make a major difference.
To see how much of difference it makes on your SWAMI run it as a secretor and as a non secretor.
For me knowledge of secretor status has made a great deal of difference in my life.