。
In short, they [women] are hungry.
Literal
Essentially they-[women] [topic-は] stomach [subject-が] is-diminished-[explanatory-のだ].
腹が減る ('stomach shrinks / becomes empty') is the idiomatic 'be hungry' — literally. 腹が減っている describes the ongoing state. 彼女たち specifies a feminine plural. のだ as the explanatory copula.