These before-and-after photos will shock you(Video)

There's no shortage of fitness transformations on Instagram. Each side-by-side image speaks to a journey: maybe someone lost weight, or bulked and gained muscle, or just squatted their way to a killer butt. But trainer John Benton's images tell a different story; his transformations highlight the exact number of inches his all-model clients lose on their hips and waist in mere weeks. Models fly to Benton's studio from all over the world to whittle down their waist-to-hip ratio—and in turn, he helps to launch their careers.

As the exclusive trainer for all modeling agencies in Dallas, Benton spends his days training only female models—but it didn't start out that way. "About five and a half years ago, one of my friends who was a booker for Kim Dawson agency—the largest model agency in Dallas—liked the way that I trained. He referred one of their girls to me—she had a lot of potential but her hip measurements were a little too big for the industry," he says. At the time, she was his first model client. "I stepped back and realized I couldn't train a model the same way I train normal girls," he says, explaining that his previous female clients had been more concerned with overall toning—particularly their posterior. "Normal girls aren't that worried about their hip measurements."

Soon Benton realized that everything he thought he knew about toning the female body—particularly as it applies to weight and strength training—didn't apply to models. "With female modeling, waist measurements and hip measurements can make or break your career, so I stepped back and through a little bit of trial and error adapted the way that I trained and changed the way I recommended diets." In just a few months, Benton's new techniques got that one client's hips from 37.5 inches to 34 inches; she eventually moved on from being the top model in Dallas to signing with an agency in New York City. It wasn't long before word of Benton's success stories spread like wildfire throughout the modeling community.

Conventional fitness wisdom says you need to do squats and lunges to tone your thighs and butt, and then chug a protein shake after working out to solidify all your hard work. That's all wrong, says Benton—if a lean model body is what you're after. In fact, studies have shown that immediately reaching for protein after a workout might not be all that necessary. "Most of the girls who come see me are already in really good shape, they’re just doing the wrong exercises for their specific model goals. They're eating very healthy already, they’re just eating the wrong types of food at the wrong time," he says. "So what we try to do in the gym is we try to burn some body fat off their hips and waist, but at the same time not build up any muscle."

His technique is a mix of cardio and isolation toning of the inner and outer thighs, hips, and waist—with a heavy focus on building a strong core. These techniques are effective on their own, but Benton trains his clients for almost two hours a day, five to six days a week to maximize their results. And what's even more astonishing is that their bodies begin to shrink within the first week. "There’s a fine line with being a model and getting a really good calorie-killing, fat-burning workout that will tone-up the areas you need to tone, and at the same time not build muscle on where you want to stay small," he says.

Non-models can also book time to train with Benton—but all that exercise might just turn you into one. It's true: Dallas native Irena Ratan, who co-owns luxury men's clothing stores called Q Clothiers and Rye 51, started training with Benton and his gaggle of models about two years ago, just before her wedding. Before going to Benton, her diet was already healthy and streamlined, and she exercised regularly by doing high intensity drills like treadmill sprints. The slower, endurance-based pace of his workouts took some getting use to at first—but like all his other clients, the results started to show in a matter of weeks.

"John told me that people would ask what modeling agency I was with—I would joke that John Benton was my agent," says Ratan, who never even considered a career in modeling. "He told me I should try it. And of course I met a bunch of girls who signed with different local agencies that encouraged me to do it, and then made an introduction." After working up the courage to take a few meetings, Ratan signed a modeling contract with a local agency in March earlier this year. "John was so excited, he’s so encouraging to all the girls—ones that are signed or ones that it's their specific goal," she says. "He really becomes way more than just your trainer. He's not only your friend, he's like your whole life coach."

It's easy to look at the thin and muscular women in Benton's transformation images and think—is this even healthy? Benton stresses the importance of his clients' already-healthy whole-food based diets, which he tweaks to be more efficient with their workout schedules—because you can't power through a two hours worth of crunches and planks without the necessary energy to do so, he explains. (Ratan says she eats a protein-rich meal like an egg white omelette before her workouts, not after.) But is training for one or two hours a day, six days a week, a good idea? We consulted two experts: Heather Milton, the senior exercise physiologist at NYU Langone’s Sports Performance Center, and Avigdor Arad, an exercise physiologist at Mount Sinai St. Luke’s. With one health caveat, both thought Benton's transformations were not all that surprising or controversial. Turns out, working out really hard—for really long—and eating well does exactly what experts think it does.

"It looks like he’s choosing more endurance rep schemes than more hypertrophy rep schemes. What that means is he’s not initiating a hypertrophy response, which is increasing the muscle size itself, but rather endurance for those muscles. So the muscles are keeping their aerobic enzymes, they're improving the leanness so there's less marbling, without increasing the size of the muscle fibers," says Milton. Muscles built for endurance rather than a bulking response are still strong—it's just a different type of strong. Milton equates it with being able to climb stairs with ease or go hiking for hours but not being able to squat a ton of weight in the gym. "They're able to maintain strength over a longer period of time," she says.

Instead of the standard squats and lunges, Benton's workouts are targeting secondary muscle groups that are less likely to increase in size. "There are different fiber types in our bodies. There are some muscles that have a greater percentage of type two muscle fiber types, and those are the ones that are able to hypertrophy much more easily," says Milton. "It looks like what he’s doing is targeting the smaller stability muscles—they are endurance muscles made-up of more type one muscle fibers that don’t hypertrophy as easily." So basically you're getting stronger and leaner and torching calories, without increasing in size.

Milton's one area of caution with Benton's transformations regards body fat percentage (she hasn't assessed any of his clients, however). "You don't want to have too low of body fat percentage, because then you actually do risk harming your hormonal balance," she says. "As long as there’s a healthy body fat percentage, which ideally for women if they’re really active is between 15 and 23 percent. If they are lower than that then yes, I would worry about their health a little bit."

You can catch some of Benton's go-to workout moves on his Instagram page—like swan crunches, plank twists, and pyramid push-ups—but he's hesitant to publicly reveal too many of his secrets. In addition to individually training models, he also does online consultations for clients around the world, helping them remotely tweak their fitness routines. "Anytime I post an Instagram video or photo my inbox gets set on fire with messages," he says. His workouts use bodyweight-only for this reason. "I do these workouts all bodyweight because a lot of my clients I'll get in amazing shape, then they sign with an agency in Milan, Paris, South Africa, or China and it's really hard to find a gym there," he notes. All his models need in order to keep toning on the road are a couple of washcloths or a resistance band—which easily fits in a carry-on. "I tell my clients to try and workout four to six days a week. Some do the full two hours but others just do one hour a day," he adds. "Once I get their hips down to 34 inches it's definitely less intense maintenance."

Benton acknowledges that female models are held to nearly impossible standards, but says that he's created a healthy way for them to achieve their sizing goals. "Even with male models, hip and waist measurements aren’t really a thing. Female models have a disadvantage to where their careers can be made or destroyed by an inch or a half inch on their waist. So we have to extremely careful with how we work out," he says. "It’s a crazy industry—but this is the way the industry is. We don’t make the rules, we just have to play by the rules and do the best we can."