The secret behind Kim Kardashian's cinched in waist

Kim Kardashian West wears two pairs of Spanx.

The 35-year-old 'Keeping Up With the Kardashians' star has admitted she puts on double the number of body shaping undergarments when she is feeling "heavier" to help cinch in her waist and give her a flat stomach.

RELATED: Kim Kardashian shows off her post baby body in GQ
RELATED: 15 times Kim Kardashian bared all for fashion

Speaking about her wardrobe essentials on her website kimkardashianwest.com, the brunette beauty said: "Sometimes I wear two pairs of body shapers on top of each other -- especially when I am heavier, I def double it up.

"My favourite styles are the Body Wrap shorts and the Spanx footless tights. I put one pair on after the other, and if there's a longer pair, I always put those on first. But usually, I wear two pairs that are the same length.

"I try not to layer two different lengths, because I don't want there to be visible seams; I want there to always just be one seam. (sic)"

And the mother of two - who has three-year-old daughter North, and six-month-old son Saint with her rapper husband Kanye West - has revealed she will wear the elastic underwear instead of knickers.

She explained: "The shorter shorts, I only wear with a short dress - instead of underwear, basically. But I prefer the super high-waisted shorts that come all the way down to my knee.

"I just recently got introduced to the footless tights, which I can wear with longer dresses like this - so you'll NEVER see my Spanx line because the seam is lower. I typically like them past the knee or right at the knee.

"They really hold you in and make you feel secure!"

Just yesterday Kim showed off her post-baby body for the first time since giving birth to her son Saint West.

Holding up a coat to protect her modestly, Kim looked sensational on the cover of GQ magazine, wearing nothing but her massive diamond engagement ring.

The TV personality worried she would never get her pre-pregnancy figure back after welcoming her second child into the world last December.

Speaking previously, she said: "There was a moment after [Saint was born] when my body was mush.

"There was definitely a moment when I looked in the mirror and I was like, 'I am never going to be the same.'"