Do you mean Black or White Worms?
I keep my blackworms in the fridge and don't feed them at all. They keep better that way and I use them up fairly quickly as a treat-supplement to the white worms...
The problem with feeding white worms fish food (in my experience anyway), is that meaty/fishy foods tend to sour the culture medium much faster. I even find this to be true with the dog and cat food some use, although not to the extent as with fish foods....
The bread/yogurt/nutritional yeast combo comes from a gentleman named David Ramsey, who was one of the AKA live food gurus that I learned a lot from. He put out an instructional video some years back. At the time, his culture had been going continuously for ten years without losing it. At that point I switched over and have had the same results.
He was using a wine fridge. I use larger culture boxes than him and keep them in the basement. I change them out every six months with fresh soil and never have a problem. With smaller boxes and using fish and/or cat food, I could have cultures start to go bad in six to eight weeks...