Less than a year after Kristin Cavallari welcomed her second child, Jaxon Wyatt Cutler, into the world, she already has her fit, slender physique back. But unlike most celebrities, the reality TV star doesn’t struggle to lose weight, but to keep it on.

Kristin Cavallari
Cavallari wants to put more muscle on

However, maintaining her toned body is quite a struggle, and the mother of two only maintains this by hard work and dedication. "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,” she told E!News.

The former ‘Hill’ star also revealed, as well as working out five times a week, she eats a very health and clean diet.

More: Kristin Cavallari Reveals How She Lost Post-Pregnancy Weight: "I'm A Freak About What I Put In My Mouth"

"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.

But her strict fitness regime does have its downsides, after Cavallari lost all her pregnancy weight, she now wants to put some muscle back on.

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"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."