Mine overate and developed severe acute swim bladder problems - swimming in spirals upside down and almost vertical! Very scary stuff. I starved him for 2.5 days and he got back to normal, and now just 2-3 Hikari gold twice a day is all he gets, with some days having 2-3 single bloodworm. They may overeat if not rationed by a caring owner! Mine overate because I had a stupid autofeeder feeding flaked food twice daily while I was away. I managed to reduce the portion size by taping over the 'catcher' hole in the feeder tube, but it was still way too much. All animals live longer with slight underfeeding (including humans), fish being no exception. Over feeding is the surest way to a) increase algae, b) pollute the tank and c) shorten the life of your fish.
I also feel that a varied diet is good for bettas. One ACer was feeding gnats - live food will be an excellent supplement to more reliable sources. We are organic gardeners at home and use not form of herbicides, weedkillers or pesticides, so over the coming summer many 'new' young greenfly (which will be plentiful) will become delicious 'between-meal' snacks for our tanks' inmates!