IT'S A MID-JULY EVENING IN THE TULSA SUBURB OF BROKEN ARROW, and several hundred people are gathered at the Arrow Heights Baptist Church for the grand finale of the Body by God Extreme Makeover Challenge, a 12-week faith-based fitness contest. The atmosphere is part athletics award banquet, part 12-step meeting. Gangs of fit, sporty-looking men and women are roaming around in jeans and running shoes. They shake hands, compliment one another's physiques, and offer hugs and ample thanks to the greatest coach of them all.

"I've tried fad diets and lost a few pounds, but then I got heavy again," says David Canavan, 48, a mustached airport security screener from Skiatook, Oklahoma. "This was the first time in ages that I've started something and finished it. I lost 48 pounds in all. When you are walking with God, and praying every day, he's going to work in your life."

"I lost only three pounds, but I took five and a half inches off my waist," Theresa Stewart, a 41-year-old naturopathic healer from Tulsa, tells me. "I have thyroid problems, and I've been diagnosed with chronic fatigue syndrome. Before I started this, my energy was so low I couldn't get out of bed."

Like most of the other fired-up contestants, Canavan and Stewart also credit their success to Ben Lerner, the evening's special guest and the man whose teachings inspired the Makeover Challenge. A 39-year-old chiropractor based in Celebration, Florida, Lerner—whose followers know him as Dr. Ben—maintains that Christians can do God's work better if they have the health and physical stamina to live long, productive lives. His edict: You owe it to God to get in shape.

Lerner has published two bestsellers that spell it all out. One-Minute Wellness: The Natural Health & Happiness System That Never Fails is a guide to holistic health that emphasizes chiropractic principles and Christianity; co-written with chiropractor Greg Loman, it appeared on the USA Today charts when it was released last August. But it's Body by God: The Owner's Manual for Maximized Living, published in 2003 and quickly hitting the New York Times and Wall Street Journal bestseller lists, that outlines Lerner's fitness program in the most useful detail.

The Body by God plan combines tips on time and stress management with low-impact aerobic exercise, basic weight training, and a diet based on low-fat, unprocessed "Foods by God": whole grains, lean meats, and fruits and vegetables. ("Foods by Man," on the other hand, are those that have been refined, pasteurized, and packaged—anything resembling a Ho Ho, Cheeto, or Slush Puppie—and are to be avoided.) Lerner promises "incredible health and outrageous happiness" for anyone who adheres to his diet-and-exercise program, which he boldly proclaims—with little or no scriptural evidence—as the one God intended for us to follow.

The focus on getting buff is a new concept for some Christians, many of whom grew up believing that the body is, in essence, a vehicle for sin and that biceps, triceps, and rock-hard abs are nothing but the fruits of vanity. But Lerner—a walking advertisement for Body by God, with his glowing cheeks and a sculpted five-foot-six frame—is more pragmatic. "There's a sense in the Christian world that you don't need to take care of the physical self," he says. "We're reminding people that the body is a vehicle for serving God."

For 30-year-old Nigel Allen, the call to follow God's fitness plan struck a chord. Over the past 84 days, Allen has dropped 24 pounds, two pants sizes, and 57 points on the cholesterol scale. "I haven't been in such good shape since I was 20, when I played minor league baseball for the Daytona Cubs," he says. When a shoulder injury ended his baseball career, in 1995, Allen joined the Army and was sent to South Korea. But after blowing out his knee in a training exercise and eventually returning to Tulsa, he found himself on crutches, depressed, and gulping eight cans of Mountain Dew each day.

"There's no feeling worse than quitting soda," Allen says. "It's worse than crack. And that's where the Body by God teachings come into play—God helps you through it. The book talks about eating five God foods a day. I changed Mountain Dew to water and carrots. Carrots are the key, man."