It still worked, says Frisk, and Chara exhales slowly, attempting to force their breathing back to something less haggard as they examine their hands. It's true- they feel less hungry. Less worn down than prior.

Undoubtedly, it still worked. The process of forcing to do so, however.

"I'm sure you'll find yourself comprehending this easily enough, mister Wright," Chara begins slowly. "but in our own world, our SAVES had a far greater capability than they did in Sol Raveh. It was only upon our arrival there that they began to affect us, and us alone."

They cast another look at Frisk, sharp eyes examining them for any signs of discomfort. And they know, without stating it, that the most likely reason for this is due to their actions. Another consequence, for their failure. Another burden.
"It's possible that being further removed from our world has caused our power to deteriorate further. In which case..."

...

"We may need to reserve it's function for emergencies only."

Which means eating again. Sleeping. Things they hadn't needed to worry about before, suddenly brought back to the forefront again when they were no longer in a place where such resources were easy to attain.

To say Chara's displeased about this revelation is an understatement.