GRAPEVINE, Texas — "It is not hard. Don't you dare tell us this is hard," Melissa Hartwig, co-creator of the Whole30 program, told the audience Tuesday. "Quitting heroin is hard. Beating cancer is hard. Drinking your coffee black. Is. Not. Hard."

Now a three-time author within the health food world, Hartwig is currently on a 10-city book tour to promote her newest brain child, "Food Freedom Forever," which succeeds both published works "It Starts with Food" and "The Whole30." Hartwig, 42, is the self-proclaimed "Whole30 Headmistress," and her 30-day program — not diet — to jump-start a healthy lifestyle is quickly gaining popularity throughout the U.S.

Established in 2009, Whole30 is a 30-day short-term nutritional reset of eating only real foods to "help you put an end to unhealthy cravings and habits, restore a healthy metabolism, heal your digestive tract and balance your immune system." This means no sugar, grains, dairy, legumes or alcohol for one month. According to the Whole30 website, the program has the potential to change the way you think about food, your tastes, habits and cravings, and even "the way you eat for the rest of your life."

After spreading the word about her program, Hartwig began to receive questions on the science behind eating and not eating certain foods and how that can affect the body. Thus, in 2012, she co-authored her first book, "It Starts with Food," which was based on the latest scientific research and served as the "why" behind the program's platform.

The first book was well-received and inspired many people to try what the program had to offer, but they were now in need of a detailed guide for the 30 days — more than what they could gain simply from the internet. This led to Hartwig's next published book in 2015, "The Whole30: The 30-Day Guide to Total Health and Food Freedom."

So what drove Hartwig to her third book, released Oct. 4?

On Tuesday night during the Dallas stop of her tour, she divulged.

"[The reaction] when you got The Whole30 was, 'This is amazing. It changed my life. I gave it to my mom, and my hairdresser, and my grandmother, and my daughter and everyone's changing their life and it feels great ... and I don't want to go back to the way I was eating. How do I maintain what I'm doing?'" she said. "And I thought, yeah, I should write that one, too. So that's 'Food Freedom Forever.'"

The new book focuses on life post-Whole30 and how to let go of bad habits, guilt and anxiety around food. In it, Hartwig defines true food freedom as being in control of the food you eat, instead of food controlling you.

"I've been testing material for this book for the last two years in various presentations in social media, in blog posts, in Q&As," Hartwig told her audience Tuesday night. "Everything I do, I do for you because you tell me you need it, and the only thing I want to do is help you succeed.

"This [book] came from all of the questions you asked me, the Snapchats you sent me, the Instagram comments, the Dear Melissa questions, searching the Whole30 hashtag on Instagram and seeing where you're stumbling and tripping and what the problem is. All of that went into this, so really you guys helped me write this book."

Hartwig's ultimate book tour stop will be next month back in Salt Lake City, where she currently lives. What can we expect next from the already bestselling author? A fourth book, Hartwig says, is already in the works.