Now in an interview with Bloomberg, she admits she doesn't like the term BBG anymore, because it implies there's only one type of body that should be in a bikini.
"Do I regret calling my guides Bikini Body? My answer is yes," Itsines said.
"That's why when I released the app (in November last year), I called it Sweat With Kayla. Sweat is so empowering. I love that."
Scrolling through Itsines' Instagram posts, it's clear she now tries to focus her message on health, not weight.
"It doesn't matter what shape and size you are, if your goal is HEALTH and FITNESS, then join the #bbg community," she captioned a collage of fan progress photos.
"She's stronger and happier now," reads the caption on another image of a fan's sculpted abs. "#bbg isn't all about weight loss! #BBG is about FEELING amazing."
Itsines was just 18, and a new graduate from the Australian Institute of Fitness, when she realised the custom-guides she created for her personal clients could reach a wider audience.
"I started uploading client transformations on Instagram, and then all of a sudden people started asking if I could come and train them from [all] over the world," she told news.com.au in 2014.
"Obviously I couldn't get to everyone, so I started developing an exercise plan people would be able to do at home."
Her plan involves a 28-minute high intensity workout, which she recommends her clients do three times a week, along with three other low intensity cardio workouts.
"I played a lot of basketball and netball growing up so I got some of my training styles from there, as well as elite athletes, standard gym moves, and I created 150 different exercises from that," she said.
"Then I paired it with a nutrition plan which I developed, but was approved by two accredited practising dietitians. The two go together, but it's the training guide is what everyone is loving at the moment.
"Girls are loving the fact that it's easy, they can download it by an e-book, it's high intensity, it challenges you, it's something new. It's not a quick fix, it's real hard work and it's a lifestyle change."
Sharing before-and-after photos has become a major part of Itsine's online marketing.
"People share with me their progress all the time, and I love sharing these with my followers to encourage them," she said.
The women who do BBG come from all over the world and there's a huge range of bodies on the #BBG hashtag.
"One I uploaded two nights ago, her body was amazing. She went from eating terrible foods to being lean and strong. Another girl was anorexic and became healthy and strong.
"It works both ways - for fat loss and for putting weight on. Your body is designed to be healthy and strong and lean."
