I know that you would like to be able to “control” your destiny by getting a third microdiscectomy and changing your diet and activities to prevent yet another herniation. Unfortunately, the chances of another disc herniation are about 50% regardless of your diet or activity restrictions.
Fusion has a very high chance of working if properly performed. Yes, there is the chance of adjacent segment disease but that chance is small. The chances are much higher of a recurrent disc herniation and/or permanent nerve damage with just another decompression.
If this was my back, I would pick the fusion by a competent and experienced surgeon.