Worms are a great source of protein. Make sure that if you dig them up yourself, they are from a pesticide-free garden.
By the way, thanks to your advice my second catfish (RTC x TSN) is eating pellets. I did not want to starve him because he is only 5 inches long. However, I said the starvation will not go longer than 2 days. On the second day, he just ate all of the Ken's pellets I gave him!!