Those conditions were meant to test the Doppelgangers' morals and self-control. To determine if their mentality would better fit with human, plant, or beast society, Leegaain needed to know how the Doppelgangers reacted under stress.
"Last, but not least, you are forbidden to reach a mass superior to that of the form that I'll assign to you. There is no point in sending you out there to learn about yourselves if you overcome every hardship simply by brute force."
In their natural form, Doppelgangers looked like a gelatinous puddle the size of an inflatable pool. They could eat as much as they wanted and either retain the mass or split into two different beings, producing an offspring.
Yet to keep the extra mass, they needed to feed regularly. Otherwise, as it had happened to Protheus, they would just not feel hungry while their bodies metabolized the accumulated nourishment until they reverted to their original size.
