cemc,
I substitute potatoes with parsnips quite often. I do a parsnip and carrot mash as a side dish and even make parsnip gnocchi. The gnocchi is seriously good -- more flavorful than potato gnocchi.
If some people find benefit from modifying their diet then that's great! I'm certainly not going to question their success or efforts. But I don't think it should be pushed on everyone.
