Dismissals by medical authorities, along with accusations of cultishness by critics like Billings, have made fruitarianism's online presence something of a viper's nest, with combative clamor that often devolves into guru-on-guru character attacks, sometimes drowning out the feel-good, fruit-for-all vibes. The community's chief rabble-rouser is Harley Johnstone, a 35-year-old Australian who calls himself Durianrider and operates a website (30 Bananas a Day) that has more than 13,000 members. With endless streams of YouTube videos and brash, exhortative blog posts, he and his girlfriend—who goes by the name Freelee and is often seen cavorting in a bikini with a banana holstered in its bottom—have become the Jim and Tammy Faye Bakker of the mango crowd. Johnstone credits fruitarianism for his transformation, in 2006, from a self-described "chronic-fatigue Nintendo zombie" into a competitive amateur cyclist with a body-fat percentage of 3. He and Freelee preach a fruit-gluttonous, hyperactive way of life that goes far beyond mere dieting: "So you don't get fat from all that fruit sugar," Freelee counsels in one video (after advising that the goal after a meal is "to look like a pregnant woman"), "spend all your free time exercising."

Despite the couple's cheeky, almost hedonistic demeanor, a brittle sensitivity clouds their message. "We will not tolerate 'anti-fruit' posts," state their forum's rules. ("If you go on any of these [fruitarian] websites and post a challenging question, you'll get banned," Billings says. "They're censoring stories of failure, which are much more common.") Johnstone, however, is such a persistent "troll" on oppositional forums—"I troll any site," he boasted during a Q&A at the Woodstock Fruit Festival—that one forum has an entire topic devoted to how to "identify and ostracize" him. A rebuttal website, 30bananasadaysucks.com, popped up earlier this year. The tagline on his personal site—"Not even two lawsuits have shut this blog down . . . the TRUTH must go on"—suggests a much darker, fists-cocked stance than do all the PEACE, LOVE, AND SEASONAL FRUIT tees on display at the Woodstock Fruit Festival. As Johnstone admitted on stage, "There's a fine line between the purity mind-set and getting the job done."

It's a line that Arnstein himself walks, despite his emphasis on getting the job done (i.e., winning races). Hanging from a chain around his neck is a gold charm that reads RAW. Viewed in the mirror, however, it says WAR. "And it is a war," he insists, with "processed food"—and the system built around its marketing and sale—the enemy. "Raw leaders are constantly being attacked because we're questioning how people live. I get hundreds of e-mails a week, some of them wishing me dead." When asked why anyone could want him dead—with the possible exception of a really paranoid Kraft Foods executive—Arnstein says simply, and without any apparent irony, "There are lunatics out there."

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Timeline: A History of Single-Food Diets
The Health Benefits of Power Fruits
Is Organic Food Really Healthier?