Centroid bodies and comparison of volumes

For −1 < p < 1 we introduce the concept of a polar pcentroid body ΓpK of a star body K. We consider the question of whether ΓpK ⊂ ΓpL implies vol(L) ≤ vol(K). Our results extend the studies by Lutwak in the case p = 1 and Grinberg, Zhang in the case p > 1.