Kristin Cavallari Explains Her Weight Issues

"I can look really skinny and I don't like that," she said.

She looks incredible and told E! News, "There's no real secret, I work my butt off in the gym. I woke up at 5:30 a.m. and went and walked uphill on the treadmill for 30 minutes."

The former "Hills" star, 28, said she works out four to five times a week and eats very clean.

"I'm the kind of person that does not eat any toxic chemicals. ... I just try to eat real food. I think probably the best tip is that I try to always get a vegetable in somehow, even in the morning if you're making a smoothie," she said.

"After I had children, my body literally changed. And now for me, it's about trying to keep muscle on and gain muscle, so that, yeah, I don't look too thin," she added. "Because I have no curves ... I can look really skinny and I don't like that look. So, yes, I'm drinking protein shakes, I'm trying to put on muscle and I'm lifting very heavy weight right now."