The former Biggest Loser trainer revealed that regardless of a strict fitness regimen, she still struggles with cellulite.
Asked about her least favourite body part, Michaels told Fitness: "My ass! I hate it! There's cellulite on it, and no matter what I do, I can't get rid of it. The reality is that it's connective tissue.
"I can starve and my boobs will go and my face will get gaunt, but I will still have cellulite. It's not so much about aesthetics for me these days. Instead, I think a lot more about the mark I'm going to make on the world than about the back of my ass."
Michaels also revealed what she believes is the real secret to her slim physique, adding: "As much as I hate it, I run every time, like three miles. It makes you skinny, that's why. It works."
She previously admitted that she weighed 175lbs as a teenager because of her troubled upbringing.