PredniSONE and natural hormones

I was prescribed 42 pills (20 days) of 10 mg Prednisone which I am to take beginning with 4 pills for four days and steadily decreasing every four days down to four 1/2 pill the last four days. I took my first dose yesterday and was told to drink lots of water. I do not wish to gain weight nor have a moon face. My doctor does not feel this will affect me in that way, but may have water retention (swelling). I am 73, and this regiment of Prednisone was prescribed to decrease inflammation due to a possible siatic nerve problem, which is causing extreme pain in my left leg. The pain is excruciating when I get up in the morning but eases down by mid morning with some pain all day and some nights if I move just the wrong way.Does anyone have a suggestion for the best foods to eat and what to avoid? I read that grapefruit juice may be beneficial.