Eating disorders are a lot like a toddler throwing a fit. He will kick and scream until he gets his way, completely unresponsive to logic.
Giving in to ED is like buying the tantruming kid the toy he wants. It reinforces the behavior.
Next time ED tantrums try observing that it's happening, labeling it as an ED tantrum and not reacting to it. By not engaging you keep ED from hijacking the situation.