Such lasting effects may be due to girls realizing not only how they were being influenced but also who was benefiting from the societal pressure to be thin.
【分析】本句为复合句，主架为 effects may be due to。girls realizing为动名词作宾语。realizing后接了两个由并列结构not only but also 连接的宾语从句，分别是how they were being influenced和who was benefiting to be thin。
【译文】这些持续的效果可能是因为女孩们不仅意识到了她们是如何受到影响的，还意识到了谁从这些让大家感到应该瘦身的社会压力中受益。