The book, released in December, provides a meal plan that includes lean protein, fruit, vegetables and whole grains, and it encourages regular exercise. The day after a two-hour rally to kick off the plan at Saddleback, he says local grocery stores were out of vegetables. “That’s the power of a congregation,” he says. “When an elephant is walking, it shakes the ground, and that’s a congregation—it shakes the ground.”

‘If you’re not following me on Twitter, TWTR +0.58% you’re going to hell,” says megachurch pastor Rick Warren, before cracking up. Mr. Warren—or Pastor Rick, as his teeming staff calls him—is leaning back in a red leather chair with his sneaker-clad feet up on the coffee table in one of his many offices on the 120-acre Saddleback Church campus in Lake Forest, Calif. He’s only joking. He has plenty of followers already: Almost 1.3 million keep up with him on Twitter, and around 30,000 attend his sermons.

Mr. Warren came up with the idea for “The Daniel Plan” a few years ago while doing baptisms “the old-fashioned way”—by physically raising and lowering people into the water. That day he baptized 850 people. “That’s about 150,000 pounds, which is why I’m so buff,” he says with a chuckle. “But as I’m lowering people, I literally felt the weight of America’s obesity problem,” he adds. “I thought, good night, we’re all fat!” Then he says he realized, “Good night, I’m fat!”

He didn’t think he could ask his congregation to get healthy without doing so himself. The following weekend, he declared he would set out to lose 90 pounds (at 6-foot-3, he weighed nearly 300 pounds) and asked if anyone wanted to join him. Mr. Warren says that he thought he might get 200 people, but by the end of the week, 15,000 people had signed up on Saddleback’s website.

Next he recruited three friends in the medical field, including Mehmet Oz, the surgeon and television show host, to come up with a system for how they would do it. Along with fitness and nutrition, Mr. Warren says he added the “special sauce” of “focus, friends and faith”—in other words, help from a higher power and from friends and community.

Named for the Biblical prophet Daniel, who challenged himself to eat only vegetables and water, Mr. Warren’s Daniel Plan instructs people to rely on “God power” rather than just willpower to eat healthily. His theory is that guilt only motivates people to follow diets in the short term, but “grace” lasts longer.

[Editor’s note: This article is incomplete. The source for this document was originally published on online.wsj.com – however, the original URL is no longer available.]