Kelly Clarkson had a ''thyroid issue'' which caused her weight to fluctuate.

The 36-year-old musician has said that she battled an issue with her thyroid gland, as well as an ''autoimmune disease'', that caused problems with her body weight, and has revealed that by following the tips in 'The Plant Paradox' by Steven R. Gundry she has been able to stop taking the medication that regulated her thyroid.

She said: ''I literally read this book, and I did it for this autoimmune disease that I had and I had a thyroid issue, and now all my levels are back up. I'm not on medicine anymore because of this book. It's basically about how we cook our food, non-GMO, no pesticides, eating really organic.''

The 'Because of You' hitmaker has been flaunting a slimmer figure recently, and insists she hasn't been hitting the gym, and instead is simply eating healthier foods.

Speaking to 'Extra', she said: ''I'm not working out! I think people think I'm working out and I'm like, 'Don't think I'm going to come play some sport!' Literally, I haven't worked out at all!''

Her comments come after she recently thanked fellow singer Carrie Underwood for ''making her feel thin'' after she was sent a package from Carrie's activewear and accessories line, CALIA, only to find that the items no longer fit her because of her recent weight loss.

She said: ''And Carrie Underwood, thank you as well because I've lost weight since you sent this. So it's all too big for me which made me feel really thin. But I'm gonna find someone that loves it.''

Meanwhile, Kelly recently vowed never to be afraid to show people what she ''really looks like'' because ''everybody'' has their flaws.

She said: ''[Full hair and make-up] is actual fake news. I think that sometimes Hollywood can be very 'Oh, we don't want people to see what we really look like. That'll be the death of you or something.' And it's like, 'Whatever!' Everybody poops. Everybody burps. Everybody's the same.''