Verb
pile on the pounds (third-person singular simple present piles on the pounds, present participle piling on the pounds, simple past and past participle piled on the pounds)
(informal) Of a person: to gain weight quickly.
I wish my parents hadn't made me feel that how I looked was linked to how much they loved me. But I do also see how hard it must be to see your child pile on the pounds and trust they'll find their own way back to a healthy weight. Arabella Weir
I tried the Atkins diet in the Seventies when pregnant with my son, as I didn't want to pile on the pounds. Now, so long as I'm healthy, I don't care what my scales say. Britt Ekland