There are two substances that instantly come to mind:
- Wax (paraffin or beeswax)
- Mineral Oil
I use both of these to protect my wood butcher block. They are both food safe, non-reactive and even relatively inexpensive. They will alter the appearance of the wood, by making it more lustrous.
I have even seen some people finish their butcher blocks with hot paraffin, using either an iron or some other gentle heat source. I cannot speak to the longevity, but by sealing out moisture and barring against some amount of microbes it would certainly improve the lifespan, although by how much I cannot say.