"Khloe's the animal -- full on animal in the gym," he reveals to ET’s Brooke Anderson. "No complaining, no bitching, no kvetching. Just gets after it."
"This is Khloe's moment," he stresses. "You can see it. The changes she's made are incredible. She's done it the right way. Nothing fast -- hard work. It's steady, hard work and it's very relatable and her body is banging right now."
Another client Peterson is fond of is Vergara -- even though the sexy 42-year-old Modern Family star has made no secret about not loving exercise.
"Her favorite thing to do in the gym is leave," Peterson jokes. "I think it's a sort of necessary evil. I don't think it's her favorite thing and I know that because of the swear words that she uses bilingually."
"Yeah, I've heard it," he laughs. "Just shy of throwing a coffee cup at ya."
As for tips on getting your own celeb-style results, Peterson has a few easy guidelines.
1. Pair strength training with cardio.
"Even if you're doing what you consider to be straight cardio, if you're on a bike for 25 or running for 25 minutes, drop down every five minutes and do ten squats, ten pushups and ten crunches," he advises. "Mix that into that same thing you're doing and watch the results."
2. "You cannot train a bad diet."
Sticking to a healthy diet, of course, is key.
"They're making good choices outside of here [the gym]," he says about his famous clients. "24 hours in a day, right? There's one in here, the other 23 you can't screw it up, and you cannot train a bad diet. So they're eating properly, they're eating at the right time, they're eating the right amounts and they're getting their rest."
"The closer you are to your goal, the more important that is," he adds about making smart nutrition choices. "If you wanna zero in, you have the diet on point. Don't look at it like a diet, look at it like a way of eating."
3. You get "cheat meals," not cheat days.
"You'll get a cheat meal, no question. It's not a cheat day," he explains. "Every day I indulge with something because if I feel restricted, I'm gonna lash out."
4. Stay hydrated, and don't go to the gym hungry.
"Hydration is everything," he stresses. "Think of this, your muscles are 70-plus percent water -- how are you not drinking water during a workout? I get the whole, 'Let's challenge ourselves, let's do that prison, tough guy thing,' but at the end of the day, you're under performing."
"You just have to start the next day," he says about recovering from a binge. "That's the only way to do it. You can't, you can't remedy that and you shouldn't fast, you shouldn't go nuts -- you should just get back on your horse."
Watch the video below to see one of Peterson's most famous clients, Khloe, show off her hard-earned abs