What's the Secret to Weight Loss: Exercise or a Healthy Diet? Popular Trainer Bob Harper Weighs In

Can a person lose weight if they eat whatever they want - pizza, burgers and chips - but have an intense workout routine? According to celebrity trainer Bob Harper, of the weight-loss TV show "The Biggest Loser," he says that is not the case.

The Los Angeles-based trainer, who was become a household name after helping countless people lose weight on the hit TV show, says it's not possible to just exercise the pounds away.

"It is all about your diet," Harper, told Reuters during a break from filming Season 15 of the long-running U.S. show. "I used to think a long time ago that you can beat everything you eat out of you and it's just absolutely not the case."

However, Harper underscores that exercise does play a vital role in overall fitness. Harper, 48, is a fan of CrossFit, which is a strength and conditioning program that combines weightlifting, sprinting and body-weight exercises done at high intensity.

While many may assume CrossFit is only for the super-fit, Harper says the program can help morbidly overweight people slim down and tone up.

"To me Crossfit just completely makes sense (as long as) you work at your level doing the things you can do with proper coaching," Harper said.

Harper has used his household name to help people at home to also lose weight. He has built weight loss empire with DVD workouts and the best-selling book "The Skinny Rules," which offers tips to drop excess weight.

He said if the 'Skinny' of his book titles and fitness DVDs is meant tongue-in-cheek, it is also the word that his morbidly obese clients attach to most.

"People say, 'Shouldn't I be fit? Shouldn't I be healthy?', and I say 'Yes, absolutely. But what I always hear from my contestants on the show is, 'I just want to get skinny.'"