We as aquarists normally feed our fish something that we can buy commercially.
We normally buy some food that has a nice picture of a healthy, colorful fish on the package. I also use some commercially available food but besides that I feed something else at every meal. Most commercial frozen food is fine and provides a nice assortment of vitamins, minerals and trace elements that our fish need but they can't provide one very important part of the fishes diet. Maybe the most important part of it's diet.
That thing is living bacteria. Fish in the sea eat whole, fresh foods every day which contains the gut bacteria of it's meal. The living gut bacteria is very important for the fishes immune system and has been studied extensively in humans "and" now in fish. Virtually all commercially available frozen food would normally be devoid of this bacteria because the food needs to be sterile so it lasts long enough to sell and ship it.
Probiotics are added to some foods in the hope of replenishing some of this bacteria and I assume that would qualify as a better food than food without it. But IMO, that is not enough. Every day I also feed, along with a commercial food, live worms, clams and new born brine shrimp. My fish are immune from just about every disease and have been for decades but that is for another thread because I am tired of people calling me "lucky" as that is not my name.
I didn't make this up as I have been linking articles about it for a couple of years. My wife came upon this just today and it is about this subject. About half way through this short video they mention fish tanks. I think it is interesting.