He is one of the more sought-after trainers among celebrities; his diet and exercise advice appear on NBC's "Today" show and in magazines like Shape.
Armed with a master's degree in exercise physiology and nutritional sciences from the University of Toronto, Pasternak's scientific background sets him apart from other personal trainers in Los Angeles. His most recent book, "The 5-Factor Diet" (Meredith Books, $24.95), hit The New York Times Best-Sellers list last year.
Life is busy for Pasternak, a 33-year-old single Jew and self-confessed foodie, who says he doesn't get much time to himself anymore. These days, he's focused on growing his prepared meal service, 5-Factor-Meal Delivery, which launched in Los Angeles this year.
Pasternak's move from Toronto trainer to Hollywood fitness maven began with a chance meeting.
Dr. Marvin Waxman, who conducts medical exams for insurance purposes whenever a film or TV show shoots in Canada, was impressed with Pasternak's scientific knowledge and introduced him to his contacts in the film industry. Those contacts led Pasternak to his first Hollywood job -- training Jennifer Lopez and Jim Cazivel for the 2001 film, "Angel Eyes."
From there, Pasternak trained Halle Berry and Robert Downey Jr. for "Gothika" (2003). Only there was a catch -- he would essentially have to work for free, because hiring a personal trainer wasn't in the budget. Pasternak said he didn't think twice.
After two workouts with Pasternak, Berry hired him to become her full-time trainer. In 2002, he moved to Los Angeles.
Working with Berry, he was able to incorporate a concept called multiple-variation training, a regimen he developed while doing research for his master's degree. Pasternak had Berry do a short, intense 25-minute workout, which included warm-up, upper body, lower body, abs and cooldown.
"The changes were so noticeable that one day while having lunch with Oprah, she commented that Halle had never looked better. Halle mentioned my name and told her that she was only working out 25 minutes a day. Oprah told her that I should write a book ... I said OK and wound up writing a book," he said.
The book, "5-Factor Fitness: The Diet and Fitness Secrets of Hollywood's A-List," (Perigee Trade, $14.95), became a top-seller. But it was his 2006 book, "The 5-Factor Diet" (Meredith Books, $24.95), that hit The New York Times list.
The diet book incorporates his understanding of nutrition, physiology and science into a simple plan based on the number five -- eat five meals a day containing five elements (protein, complex carbohydrates, fiber, fat and fluids); work out five times a week with five exercises -- that features no calorie counting or weighing food.
"It really is about lifestyle," he said.
In a town renowned for celebrity-endorsed fad diets, Pasternak's numerically gimmicky program has piqued the interest of diet experts, who are divided over its viability. Some, like New York University Medical Center nutritionist Angela Kurtz, see it as a "well-balanced eating plan that includes all the food groups" that will leave you feeling full. But others, like Toronto-registered dietitian Susan Finkelstein, say there's no mechanism in place to address portion control or emotional overeating.
But Pasternak doesn't concern himself with portion sizes. Instead, he said, he tells his clients simply to use common sense.
Pasternak steers clients and readers away from any foods made with refined flour and added sugar. Among his must-have foods: egg whites, seafood, beans, vegetables, salsa, mustard, jerky, no-flour crackers, water and sugar-free juice.
Pasternak also recommends keeping a food journal.
"You'd be amazed at how much you are eating throughout the day. So, start tracking to understand your current habits," he said.
In addition to tracking eating habits in your food journal, he recommends adding stars next to meals you love so you can put them in heavy rotation and including grocery lists to shop smart.
The 5-Factor Diet also provides a "cheat day," which allows devotees a day to eat whatever they want. But he recommends clearing the pantry of temptation foods.
"I find that its best not to have your favorite cheats on hand the rest of the week," he said.
For more information, visit http://www.5factordiet.com/