Reality TV star Kim Kardashian West has been using a waist training corset because it helps make her famous derriere look bigger.

The "Keeping Up with the Kardashians" star revealed on photo-sharing website Instagram that she had been using the tight-fitting corset to help her stay in shape.

Her friend Premadonna, who owns Waist Gang Society, says the blonde beauty hopes the garment will help boost her curvy frame, reports femalefirst.co.uk.

"Kim uses the trainer to lose weight but also to maintain her shape. It slims the waist which emphasises the bottom too. She's obsessed with it," she told Grazia magazine.

According to Premaddona, Kardashian can expect to lose up to two inches a week if she wears the garment for six hours a day.

She said: "The waist trainers are made from a combination of Lycra, spandex and latex and they work by pulling you in around the middle. The material makes you sweat more around your waist -- meaning you lose inches in that specific area. It gives you that hourglass shape."

The 34-year-old star, who has 21-month-old daughter North with husband Kanye West, is so dedicated to using the corset she carries one in her handbag wherever she goes.

"Kim carries a waist trainer in her handbag everywhere she goes. She wears one in the gym, which means she gets quicker results, or when she's running around ahead of photo shoots.

"You can wear it under dresses on the red carpet too. Some customers even sleep in it," Premadonna added.