What diet should my 18 year old son have? He has protein s deficiency and lupus, he is life long dependent on warfarin and has regular INR testing

Diet depends. If the diet has an effect on the warfarin this could be a problem. You need to discuss with his physician.
With the. Need for warfarin it is important to have a consistent intake in green leafy vegetables as they contain vitamin k. If this is erratic it makes it difficult to regulate the inr.