I have undergone 3 surgeries for nasal polyps, been on steroid nasal sprays, and been on steroid saline irrigation. I no longer use prescription medicine, instead I am on a B vitamin supplement.
My doctor and I accidentally found out that I had been cured of nasal polyps when I went for a check up and the doctor found no polyps despite the fact that I had stopped my nasal steroid 3 months earlier due to vaccinations I was receiving. Over the next year, I did detective work to figure out how I did it. Initially, I thought it was zinc, fish oil, and B vitamins. However, I stopped the zinc and the fish oil years ago and the polyps are still gone. The only supplement I take now is a daily B vitamin pill. B vitamins are important for keeping one's skin healthy; so, my guess is that the B vitamins keep my skin strong enough to prevent bacteria, viruses, and fungi from breaching it and causing infection and inflammation and the resulting polyps.
On a side note, I was supposed to have a 4th surgery in 2007. I went for a third opinion, and that doctor said that he could get rid of the polyps without surgery. He gave me oral prednisone AND had me put budesonide (liquid prednisone) in saline solution and irrigate my nasal passages twice a day. The polyps were completely gone in 2 months.
On another side note, my friend's doctor told her to go on a migraine free food diet to stop her sinus infections. I have found that avoiding certain migraine trigger foods (almonds and oranges for me) keeps me from getting sinus congestion. Avoiding sinus congestion probably helps prevent the polyps by keeping bacteria from growing in all that stagnant sinus fluid.