Whole30 lifestyle creators Melissa and Dallas Hartwig have new diet book coming in April

Melissa and Dallas Hartwig, best-selling authors and managers of the popular Whole30.com lifestyle site, have a new book coming out in April.

Houghton Mifflin Harcourt announced Thursday that "The Whole30: The 30-Day Guide to Total Health and Food Freedom" is scheduled for April 21. The publisher is calling the book a step-by-step guide to losing weight and improving health.

The Hartwigs founded the Whole30 program in 2009. Their previous book, "It Starts With Food: Discover the Whole30 and Change Your Life in Unexpected Ways," recently was on The New York Times' best-seller list for "food and fitness."