NOT LONG AGO, I abandoned my faith. Spiritually, I'm still a mildly observant Jew, but my commitment to perfect health is over.

It wasn't an easy break. I've been an aggressive athlete for years, skiing and mountain-biking competitively in college and running six marathons since 1999. But when I moved to New York several years ago, I suffered a health crisis. Training to run a sub-three-hour marathon, I grew obsessed with my fitness and nutrition. I voraciously consumed books and magazines offering get-faster secrets. I scrutinized my diet, going so far as to weigh my food, à la Lance Armstrong. Constantly worried about hydration, my Nalgene became an appendage. My older brother found this habit weird. Eventually, I realized I was weird.

Yes, I'd achieved my goal—2 hours 56 minutes in the New York City Marathon—but I'd become a miserable tightwad and forgotten why I loved running in the first place. That is, I'd contracted the same rabid fitness-mania that's currently ruining so many athletes. Recent years have seen a profusion of regimens, menus, and treatments for the country's rapidly growing number of endurance junkies. But in our quest for perfection, we've become a mass of anxious obsessives, soaking up each new trend, sports study, and diet to fix such normal human ailments as tight hamstrings and the occasional loose stool.

Last year, Americans purchased 30 million fitness books. Meanwhile, the personal-training industry has grown 31 percent since 2000. When I signed up at the enormously popular Equinox fitness chain (which in seven years has expanded from ten to 42 locations), my membership included a free training session. My barrel-chested trainer threw me on a treadmill for a quick "test" of my VO₂ max. Then he used the fuzzy results to tell me that everything I knew about running was wrong. I left confused. Later, when I learned that there's no national certification exam for trainers, and that at least six competing organizations offer licenses, I got pissed off.

Nutrition presents an equally troubling minefield of curious information. Men's Health recently published an ominous "20 Worst Foods" list filled with such horrifying items as an 1,145-calorie turkey burger—the kind of meal I used to love after a long run.

And then there's the wheat-allergy fad. In 2006, the National Institutes of Health launched the Celiac Disease Awareness Campaign to alert the public to the dangers of wheat. For the few diagnosed with celiac, the condition requires a strict gluten-free diet. But according to the N.I.H., the condition affects only 1 percent of the population. You wouldn't know this, given the arms race of wheat-free cookbook and gluten substitutes now under way. Whole Foods runs a gluten-free bakery in North Carolina that churns out celiac-approved items for the upscale supermarket chain's outlets nation­wide. As The New York Times reported in 2006, one woman was so convinced she suffered from a host of food allergies that she purged her diet of all citrus fruits—only to get diagnosed with scurvy.

In the frenzied bid for 100 percent perfect health—via perfect diets and workouts—we've certainly become more fit, but we've lost our reason. Which is why I've decided to stop at 98 percent. It's that last 2 percent that's driving us crazy.