15-year-old loses 100 pounds to reach bodybuilding dream

MacKenzie Walker lost 100 pounds with diet and exercise. 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. 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.