I'm definitely not an expert. I know when I received my worms it recommended giving the worms corn meal, to give them a boost after shipping. I continue to give it to them now and then. It would be awesome if I soil expert would answer your question. Until that happens, I will share my thoughts. With just about everything what goes in comes out. So if you eat home grown organic food, you are giving yourself a great chance to be healthy, if you live on fastfood, not so much. I use this philosophy with all my animals, including my worm. They get a variety of my best food scraps. It just seems like the better quality food scraps would make better quality casting. The variety is because different foods have different nutrients, so it seems to me I will get a more well rounded balanced casting this way.
In all honesty I have chosen quantity over quality when it comes to the bedding. I started out using wood chips. In my mind I felt this would give me a more natural quality casting. Maybe it did, who knows, I didn't have it tested. But, yes you knew it was coming. It took 8 or 9 months to get usable worm castings. I would have to have many bins to get enough worm castings that way. So I have gone to the dark side so to speak. I shred cardboard and use it as the primary bedding. I do add Coco Core, and some rough compost. I know there's a lot of controversy about cardboard, and the glue used, and I wish it wasn't so. We have an abundance of cardboard, and the worms brake it down pretty fast. 6 to 8 weeks instead of months. So for us getting rid of cardboard, and faster results wins over what in my mind would be the "better, more natural" choice.
Basically in my mind the better quality you give, the better quality you get. Good luck.