  The effects of meson loops in the vacuum sector of the Nambu--Jona-Lasinio
model are calculated. Using the effective action formalism we take consistently
all next-to-leading-order $1 \over \Nc$ terms into account. This leads to a
symmetry-conserving approach, in which all features of spontaneously broken
chiral symmetry, such as the Goldstone theorem, the Gold\-ber\-ger--Treiman and
the Gell-Mann--Oakes--Renner relations are preserved. Contributions to $\langle
\overline{q}q \rangle$ and $F_\pi$ are calculated, and are shown to be
substantial, at the level of $\sim 30\%$, consistent with the $1 \over \Nc$
expansion. The leading nonanalytic terms in the chiral expansion of $\langle
\overline{q}q \rangle$, $F_\pi$ and $m_\pi$ agree have the same form as the
one-loop results of chiral perturbation theory.
