Kelly Clarkson is known for loving the skin she’s in, and even with her new look, that body positive attitude hasn’t changed.

For weeks now fans have noticed the multi-platinum music star, 36, looking decidedly more trim as she capped off her winning first season as a coach on The Voice and hit every stage from the Billboard Music Awards to the CMT Music Awards.

At the latter last week, she finally opened up about her weight loss telling Extra in a red carpet interview that she’d taken to a new “clean eating” regimen after reading the book The Plant Paradox. “I did it for this autoimmune disease that I had and I had a thyroid issue,” she said.

In this week’s issue, a source tells PEOPLE that the changes Clarkson has made are for her overall health and wellness. “Weight loss wasn’t the goal,” says the source, confirming that Clarkson has now lost about 37 lbs. “This was an overall health approach.”

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After being diagnosed with a problem relating to her thyroid (an endocrine gland that stores and produces hormones and can affect energy and weight), the singer picked up The Plant Paradox, a 2017 book and corresponding dietary regimen that advocates so-called clean eating and reducing consumption of foods high in proteins called lectins.

Clarkson based her diet on the bestseller by Dr. Steven R. Gundry — which advises cutting several types of whole grains, dairy products, nuts and vegetables such as tomatoes, claiming they cause harmful inflammation, a theory that has been debated.

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“It’s basically about how we cook our food, non-GMO, no pesticides, eating really organic,” Clarkson said of becoming a Paradox convert. Now “All my levels are back up. I’m not on medicine anymore because of this book.” (Nutritionist Dawn Jackson Blatner tells PEOPLE, “It’s not the absence of lectins that’s magical; it’s that people following this plan aren’t eating pizza [and] baked goods.”)

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According to the source, “[Kelly] had already lost a ton of weight when I saw her in March.” But the outspokenly body positive singer — who’s taken body shamers to task over the years and once told Attitude magazine she was “miserable” being skinny — never set out to change her appearance.

For more on Kelly Clarkson’s new health journey, pick up this week’s issue of PEOPLE, on newsstands Friday.

“There were reports that she had gone on some extreme diet, and that’s just so the opposite of what she stands for,” says the source, who adds that Clarkson’s husband, Brandon Blackstock, has joined her on the new health journey.

Adds the source, “Kelly’s one to love her body no matter what size she is.” But most importantly, “She’s very happy and feels great!”