If you follow either Kim or Khloe Kardashian on Instagram—which we suspect you might—you’ve probably seen them post a pic or two wearing a corseted device called a “waist trainer” that—as the name suggests—makes their waists look abnormally tiny.
In case you’re not one of the reality stars’ nearly 50 million combined followers, waist trainers are tightly constructed bands of material that are designed to smooth your waistline and give you an instant hourglass shape. From the pictures that the Kardashian sisters have posted, the waist-trainer can quite literally make your waist look like you just stepped out of a Victorian novel.
The Kardashians aren’t the only fans of the waist-defining apparatus. Jessica Alba has sung high praise of the device, crediting waist-training for helping her get her body back post-baby and has even created her own line of corseted trainers for new moms.
But, do they really work? Caroline Apovian, M.D., professor of medicine at Boston University School of Medicine, broke down the benefits, and repercussions, of avidly using waist-training devices to Health.com, and apparently the results aren’t quite as magical as Kim and Khloe make them out to be.
Dr. Apovian says the devices are best when seeking temporary results—a big night out, for example—and have very few lasting benefits. In fact, there’s no evidence that the device can permanently reshape your body or trigger fat loss.
Your next question is probably going to be: Is waist training safe? Well, some experts believe it might actually have the opposite-than-desired affect and make your core weaker rather than stronger. Also, frequently using the device can cause heartburn and stomach pain, something Apovian attributed to the fact that our stomach might get pushed up beyond the diaphragm, which could cause reflux.
One thing you should never, ever do? Work out while wearing a waist trainer. The device constricts your breathing, which is extremely dangerous when doing any sort of physical activity.
Bottom line: Testing out the waist training devices isn’t necessarily a bad thing if used correctly and in moderation. Wear them under your dress for an instant hourglass shape next time you have somewhere special to go, but don’t obsess over them, or expect them to permanently or drastically alter the shape of your body—no matter what Kim Kardashian’s Instagram may tell you.