I can only tell you what I do... (and what works for us)...

I don't overfeed. They each get 2 presoaked betta pellets in the morning, and 2-3 (frozen/thawed) bloodworms in the evening. My tiny boy betta... Charlie... gets only 1 pellet in the morning and no more than 2 medium sized bloodworms in the evening - as I noticed that if I feed him what I feed the others... he gets quite bloated in the tummy area. Every Saturday morning... instead of the pellets... they get some pea. I haven't had any constipation issues with this regimine. They also get a bit of mirror-time each day (for exercise)... and for most of them... it coaxes them to have a bm! lol! I haven't had to fast them doing this (yet... but will if I need to).

Fasting one day a week is also a good thing.... and works for many bettas. Their systems are built to go without food for several days actually (as in the wild... this could often be the case). This regimine works for many betta keepers (fasting 1-2x a week - skipping a meal).

Try what you are most comfortable with... if it doesn't work... then try another method.

Michele