Gigi Hadid is famous for her Victoria's Secret model body, but she says she's had to switch up her self-care routine in 2016 because she lives with Hashimoto's disease, an autoimmune condition.

"My metabolism actually changed like crazy this year. I have Hashimoto's disease," Hadid told at the Reebok #NeverPerfect panel in New York, where she sat alongside Lena Dunham and Olympic gymnast Aly Raisman. "It's a thyroid disease, and it's now been two years since taking the medication for it, so for the VS show I didn't want to lose any more weight, I just want to have muscles in the right place, and if my butt can get a little perkier, then that's good."

Hashimoto's is a condition in which one's immune system attacks the thyroid gland, according to the Mayo Clinic. It can lead to an under-active thyroid, which often causes recurring fatigue, weight gain, muscle weakness and hair loss.

Fortunately, Gigi's evidently feeling healthy and (literally) kick-ass, as she led a self-defense kickboxing class before sitting down for the panel. The model extolled the virtues of learning to defend oneself following her quick reaction to a physical attack by a man named Vitalii Sediuk in Milan back in September.

"GIRLS, prepare yourselves so that, if you ever feel in danger, MUSCLE MEMORY can fight back for you," Hadid tweeted, in reference to the elbow jab she threw as the man grabbed her from behind and lifted her off the ground.

Read more quotes from Gigi – including "literally, screaming into a pillow helps" — over at Elle.

Backstage at the Victoria's Secret Fashion Show: Gigi, Bella, Adriana and More