The American Idol alum hasn't been shy about showing off her weight loss since she started shedding the pounds. She's lost 37 pounds without exercise, all thanks to a book called The Plant Paradox.
"Everyone keeps asking me, so I'm like, 'It's not a secret!' I just read a book," Clarkson told ET last month. "It's basically kind of rethinking everything, kind of how we eat processed foods, how we spray our foods, how we treat antibiotics like it's Tic Tacs."
"It's a really great book that changed my life," she added.
Clarkson is definitely proof The Plant Paradox can work, but how can everyone else implement the diet? ET's Keltie Knight sat down with the book's author, Dr. Steven Gundry, who revealed everything you need to know about the diet plan.
"I used to be 70 pounds bigger than I am now despite running 30 miles a week and going to the gym one hour a day," Dr. Gundry reveals. "And so I eliminated foods that turned on our immune system, which are called lectins."
But what exactly are lectins, and how can we avoid them? Here's five things you need to know about going lectin-free.
1. You're probably eating a lectin-high diet
Lectins, as Dr. Gundry shared, are carbohydrate-binding proteins, found in the skin and seeds of vegetables like tomatoes and cucumbers, as well as plant-based foods like grains, oatmeal, brown rice and pasta.
"Over the last 50 years, we have increased our lectin consumption unknowingly and coinciding with that, our autoimmune system has skyrocketed," he explains.
2. Swap out foods containing lectins
"The first thing you do is make some swaps, just like Kelly Clarkson did," Dr. Gundry says.
"So, you get rid of oatmeal. It's a grain, a really nasty grain, you get rid of brown rice, you get rid of whole wheat. There's some great substitutions that don't have lectins. For instance, this is millet. Some people call it bird seed. Sorghum is fantastic," he continues. "When you remove them, weight loss is the natural consequence."
3. Choose your cooking method wisely
Dr. Gundry is a big fan of beans -- after a round in the pressure cooker.
"Beans are great for you with one problem... they are some of the highest lectin-containing foods there is. If you pressure cook them or even buy them pressure cooked, then they're perfectly safe and really good for you, but beans by themselves are no good for you," he explains, warning people to stay away from slow cookers.
4. Skip breakfast
"What I'd actually like people to do is not eat breakfast. It's actually the least important meal of the day," Dr. Gundry claims. "Do you think our ancestors crawled out of our cave and said, 'What's for breakfast?' There wasn't any breakfast. There wasn't any storage system. We had to find breakfast and maybe that was lunch when we broke fast. That's what breakfast means."
5. Go nuts
"Eat nuts!" Dr. Gundry suggests. "Get a handful of walnuts, eat them everyday."
See more on Clarkson's recent weight loss in the video below.