Celebrity trainer Bob Harper, of the weight-loss TV show "The Biggest Loser", has built a career putting very obese people through some gruelling fitness paces but if he's learned anything from the experience, it's that diet trumps exercise every time.
"It is all about your diet," Harper, 48, said during a break from filming Season 15 of the long-running US 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."
Harper has spun his TV fame improving the fitness of people who are 100 pounds (45 kg) or more overweight into an 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.'"
In addition to promoting a healthy diet, a big part of his exercise routine includes lunges and other core-strengthening moves to burn enough fat to let the inner six-pack shine through.
Harper said the workout is aimed at getting the heart rate up because that's when people are going to be able to burn fat and when fat is burned off, the abdominal muscles are exposed.
Crossfit makes sense
He also adheres to the no-frills strength and condition program called Crossfit, which is a series of timed, ever-changing physical challenges that he says are suitable for everyone.
"I'm working with people who are 500 pounds (227 kg) and doing Crossfit on a regular basis," said Harper, who described the approximately 20-minute workout as well-balanced.
"To me Crossfit just completely makes sense (as long as) you work at your level doing the things you can do with proper coaching," he explained.
But Dr. Mark Kelly, an exercise physiologist at the American Council on Exercise, said that even with supervision, Crossfit can be risky if the fitness groundwork isn't in place.
"Crossfit has very ballistic training. You're asking people to move fast through a large range of motion. Even with coaching, the foundation of stability, mobility and psychomotor skill has to be laid (first)," he said.
Kelly agrees that diet is the main factor that can lower weight, but it's exercise, he adds, that allows that lower weight to stick.
He cited the National Weight Control Registry, a research study that includes people 18 years or older who have lost at least 13.6 kg (30 lb) of weight and kept it off for at least one year. Ninety percent of those in the study exercise regularly.
"They're the biggest losers across the nation," Kelly said. "And the No. 1 thing they did was exercise on a regular basis. Many simply through walking."
Harper said he values working with people who have gotten far off the diet and fitness track more than the celebrity status conferred upon him by reality TV.
"Of course with everyone being on a television show, from people working on fishing boats to people being interior designers, you get this platform," he said. "But I think for me, celebrity trainer is not who I am."
He is, he said, someone who has found what he loves to do.
"When you find your passion, it makes for a good life."