Harley Pasternak is a fitness and nutrition specialist who boasts the largest celebrity client roster in the industry, and has worked with the likes of Ariana Grande, Charlie Puth, Lady Gaga, Rihanna, Halle Berry, Katy Perry, Pusha T, Megan Fox, Robert Downey Jr., Robert Pattinson, Jessica Simpson, Gwen Stefani, Adam Levine, Charlie Puth, Kanye West, Kim Kardashian, John Mayer, Amy Schumer, Alicia Keys, and Jennifer Hudson.

He's also a New York Times Bestselling Author whose books include 5-Factor Fitness, 5-Factor Diet, The 5-Factor World Diet, The Body Reset Diet, The Body Reset Diet Cookbook, and 5 Pounds.