Throughout Lauren Fleshman’s career as a long-distance runner, “It just seemed like anything associated with womanhood was an impediment to success,” she says. Although she was a five-time N.C.A.A. champion at Stanford, once she turned professional she learned to see her curves as a liability. She honed her frame by restricting calorie intake, which stopped her monthly periods, too. At the time she felt liberated from the hormonal swings that had made her resent her female body.

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