The actor reveals to PEOPLE Now that he set about making a major lifestyle change after some tough love from costar Shiri Appleby.
Bierko – who plays Chet, the creator of a Bachelor-esque reality show on the Lifetime hit – admits he had let himself go a bit before being cast in the role.
He recalls getting a reality-check the early days of filming: “I sat down next to [Shiri] and looked at myself in the monitor last season, and I saw I was kind of heavy.”
After Bierko, 51, acknowledged that he’d “put on a little weight” but suggested he only needed to drop around 15 lbs., Appleby, 37, didn’t mince words. “She went, ‘FIFTY,’ ” Bierko recalls, adding that she told him he “got fat.”
So how did the star shed the excess bulk – and how has he kept it off?
“You need structure,” he advises, likening the process of successfully losing weight to enlisting a piano teacher to learn how to play rather than trying to figure it out yourself.
UnREAL airs Mondays (10 p.m. ET) on Lifetime.