JACKSONVILLE, Fla. — After last Sunday night’s service at Celebration Church, where a 10-piece band played Christian rock for 1,600 worshipers, Stovall Weems, the pastor, met me in his “green room” and offered nibbles from a tray of kiwi, pineapple and melon slices.

In a showbiz green room, the fruit is for waist-conscious guests. But backstage at Jacksonville’s largest church, Mr. Weems — a muscular, friendly guy you desperately want to call “dude” — stocks fruit because it is all some of his staff members are eating right now.

For the rest of January, the pastor will not eat even that.

Mr. Weems has fasted periodically over the last 20 years, ever since, as a coke-snorting Theta Xi brother at Louisiana State University, he found Jesus and joined a group that encouraged fasting as a way to draw closer to God.

Twelve years ago, believing that God called him to Jacksonville, Mr. Weems founded the evangelical, nondenominational Celebration Church. As it grew to more than 10,000 worshipers a week, at 12 campuses, he always preached a combination of fasting and prayer for spiritual growth.