Strawberries and oranges have Alkaline effect on body

I've been reading information on balancing the PH levels in the body. The lists I've found on the internet and in books say that strawberries and oranges act as Alkaline agents on the system as opposed to Acidic. Why do you suppose they are on the Avoid list for type O for their acidic properties??? Thanks in advance for any light you can shed on this subject for me. :) Tweet