(CNN)At 15, MacKenzie Walker has accomplished more than most people twice her age. She's written a book. She's started a business, training and coaching clients online. She's amassed nearly 60,000 Instagram followers.
And perhaps most impressive, MacKenzie has lost -- and kept off -- 100 pounds.
"She never misses the gym," her dad, Scott Walker, said. "If I say, 'I want ice cream,' she said, 'Dad, I don't have the (macronutrients) for that.' She won't cheat on her diet."
MacKenzie dreams of being Ms. Olympia, the world's best female bodybuilder. Envisioning her in that role is a bit of a stretch for strangers looking at her tiny 5-foot-5-inch frame. But those who know what she's already done to reach her goals have no trouble imagining it.
