Reluctant gym goers rejoice! Diet NOT exercise is the key to weight loss, claims leading personal trainer Celebrity trainer Bob Harper, of the weight-loss TV show 'The Biggest Loser', has said that for significant weight loss, diet is key Admitted that he once believed people could 'beat everything they eat out of them' but that he has since discovered this simply is not true Still believes fitness is essential for health but for those who need to need to lose weight, food should be the focus Bob Harper said that he once thought you could work everything you eat off, but that in reality it isn't that simple 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. The Los Angeles-based trainer, who was born on a cattle farm in Tennessee and arrived in California some 20 years ago, said gone are the days when he believed it was possible to just exercise the pounds away. 'It is all about your diet,' Harper, 48, said 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.' 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. 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. Don't sweat it: Those who are keen to lose weight must address their eating habits if they really want to shift the pounds. Exercise is, however, still essential for fitness and wider health '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.