  We evaluate the mass polarization term of the kinetic-energy operator for
different three-body nuclear $AAB$ systems by employing the method of Faddeev
equations in configuration space. For a three-boson system this term is
determined by the difference of the doubled binding energy of the $AB$
subsystem $2E_{2}$ and the three-body binding energy $E_{3}(V_{AA}=0)$ when the
interaction between the identical particles is omitted. In this case:
$\left\vert E_{3}(V_{AA}=0)\right\vert >2\left\vert E_{2}\right\vert$. In the
case of a system complicated by isospins(spins), such as the kaonic clusters $
K^{-}K^{-}p$ and $ppK^{-}$, the similar evaluation impossible. For these
systems it is found that $\left\vert E_{3}(V_{AA}=0)\right\vert <2\left\vert
E_{2}\right\vert$. A model with an $AB$ potential averaged over spin(isospin)
variables transforms the later case to the first one. The mass polarization
effect calculated within this model is essential for the kaonic clusters.
Besides we have obtained the relation $|E_3|\le |2E_2|$ for the binding energy
of the kaonic clusters.
