Purposefully withholding food is cruel and serves no purpose except to let the bird know that you can't be counted on for it's basic needs. This is not the way to build trust, and it can create psychological issues that the bird will carry with them for the rest of their lives.
Weeks? Care to cite your sources on this?
The smaller the bird, the less time they can go without food.
Humans are also resilient, when is the last time you went days or weeks without food? Have you ever thought about how it would feel to have someone withhold food from you for days or weeks?
No animal should ever have to worry about whether they're going to be fed. Not for a day or any other amount of time.
You know what works better? Allowing your bird to take however long he needs to trust you. That is what creates a true bond that is based on mutual respect, rather than one based on fear or hunger.
I saw your other thread here:
Weird eating behaviour
With what you've shared in this thread, it sounds like they are eating so much because they have no idea how long they will have food.
I had a cockatiel who suffered some kind of food trauma before he came to us, and he frantically ran to his dishes as soon as the food went in and ate until he couldn't hold anymore. He did this for all the years we had him, and it was heartbreaking to see.
I want to plead with you to change your training methods. I believe that you will be pleasantly surprised at how much stronger the bond will be that you are able to create with your birds when the bond is based on trust and respect.