We frequently assume feeding live foods (exclusively or sporadically) will provide all the nutritional value needed, but they will not unless you can use a variety of suitable live foods. For example, wingless fruit flies, newly hatched brine shrimp, insects collected outdoors provided you can be certain of their cleanliness and lack of any pesticides, fertilizers, etc. Worms are not good except as rare treats, and this means very small worms and well cleaned out worms (I read an article on how to clean out earthworms many years ago, feeding them something I can't remember now, but it seemed like a lot of bother for so little or no actual value). Live insects are more "natural" for most fish, then crustaceans.
We have high quality prepared (dried) foods today that do provide everything needed, with minimal fuss. Fluval Bug Bites has been mentioned, and for all omnivorous and carnivorous fish these frankly cannot be equalled for their health value. A quality flake food would be good for bettas, like New Life Spectrum basic flake. It is generally recommended that you feed a variety of good foods, at least two or maybe three. Flake and pellet foods that contain whole fish, not fish meal, and no cereal meal, are preferable.