Spanx are the worst-kept secret of many celebrities. Katy Perry, Adele and Kim Kardashian have all become fans after Oprah Winfrey endorsed Sarah Blakely's company on her show in 2000.

But other celebrities have publicly said how uncomfortable they are.

The Help star Octavia Spencer confessed on the Ellen DeGeneris Show to wearing three Spanx. She said she could not party because she was “being pinched in places I didn't even know was possible!”

But are Spanx only uncomfortable, or are they actually bad for you?

Here are a few things to consider before you break out your Bridget Jones's Diary-style underwear for your next first date.

Spanx are tight – after all, they're designed to hold in the problem bits – but they also compress your gut, which can exacerbate existing health problems.

Gastroenterologist Peter Katelaris says: “If someone is prone to gastro-oesophageal reflux, compressing the abdomen may raise intra-abdominal pressure and provoke reflux episodes.”

He says for people with gut symptoms such as bloating, tight clothing such as shape wear could be uncomfortable.

Spanx can also put pressure on your diaphragm, reducing the amount of room the muscle has to expand, which can leave wearers light headed and breathless, according to the Huffington Post.

As well as affecting your gut, Spanx can affect the circulation in your legs and even cause tingling, numbness and pain by compressing the peripheral nerve in your thigh, says chiropractor Karen Erickson in the Huffing-ton Post.

Erickson says especially if worn while sitting, Spanx can create varicose veins for those genetically prone to them and also cause swollen ankles.

Should you avoid wearing Spanx altogether?

Katelaris says that while there are no medical studies on the effect of Spanx, when it comes to compressive clothing moderation is sensible.

“Commonsense tells us that if it is uncomfortable and provokes symptoms, the choice has to be made about not wearing it or putting up with the symptoms,” says Katelaris.

So while Spanx are all right to wear occasionally, it is best to avoid wearing them for a long day at the office.

If you decide to wear them, it is important to make sure they fit properly. If the garment is cutting into your body and you find the underwear hard to get into or out of, you probably need a different size.