Gigi Hadid made a big announcement during a panel with Reebok on December 7. Hadid sat alongside Ruby Rose, Aly Raisman, Zoe Kravitz, and Lena Dunham and bluntly talked about her social media detox, her career so far, and her health. She also spoke about her ailments when she revealed that she has Hashimoto's, a thyroid disease, Elle reports. The 21-year-old said she has been taking medicine for the disease for the past two years, but still struggles to maintain a normal metabolism. She spoke about the disease in reference to her weight loss and muscle gain for the Victoria's Secret Fashion Show. "My metabolism actually changed like crazy this year," she told the crowd. "I have Hashimoto's disease. 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 also called chronic lymphocyctic thyroiditis, according to The Mayo Clinic. Luckily, treatment of the disease is simple and effective. It occurs when someone's immune system attacks the thyroid gland, which controls our bodies' hormonal functions. Although it is most often found in middle-aged women, it can occur in men and women of all ages. Unfortunately, Hadid's mother and younger sister, Bella, 19, both have chronic Lyme disease, which comes with much more severe daily ailments.