Free Republic

In 2011, Allie Kieffer ran a 4:40.9 mile and placed third in the USA Track & Field Indoor Championships 3,000-meter event. She was fast. But she wanted to be faster. “We often hear that to run faster, you should lose weight,” Kieffer says. At 17 percent body fat, the now 32-year-old was already lean, but “everyone seemed leaner than me.” So, as she made the jump to the elite scene, Kieffer began cutting calories and fat. She lost 10 pounds and qualified for the upcoming Olympic Trials. She also developed a stress reaction in her tibia. Not only did running...

You do too much too soon Many people try to overhaul their diets while simultaneously logging monster workout sessions at a pace that’s unsustainable. "People get all excited about counting calories, they overexercise and undereat, and it ends up being too much restriction," says exercise physiologist Jenny Hadfield, founder of coachjenny.com. "Three weeks after they start, they can’t manage it, and the scale tips the other way." Without adequate fueling, workouts become a waste of time; with no energy to push their bodies faster, harder and longer, people can’t make substantial fitness gains. And the body rebels, Hadfield says. "When...