A word of caution... Pro-Gold is serious stuff, it is what professional goldfish breeders use to get the best results in their fish. If you look at
http://www.goldfishconnection.com (makers of Pro-Gold) and check out their fish gallery, you will know what I mean. For top of the line showfishes, fat is desired, and rest assured that Pro-Gold will make your fish fat!
I've only fed Pro-Gold to my little fishies for a week and they're already noticably fatter! I believe to keep a goldfish lean you must keep the protein in the diet to 30% or so. I think Pro-Gold has like 60%...
Also, if you do feed your fancy goldfishes any of these foods, do not forget to also use a spirulina flake or peas as supplement... their shape means that their digestive tract is not as straight as common goldfish (or any fish) and it must be cleaned out with one of these natural laxatives at least twice a week or so.