She is the co-creator of a series of fitness ebooks titled Bikini Body Guides, and a meal-planning and workout app, Sweat with Kayla.

[4][5] In March 2016, Time named Itsines one of the 30 most influential people on the Internet, noting her success at leveraging social media to promote her brand.

[9] Finding that she enjoyed how the workouts made her feel, she abandoned her original plans to become a beauty therapist[10] graduating from the Australian Institute of Fitness at the age of 18[5] as a Master Trainer.

[5] Itsines came to believe that most women seek three specific outcomes from training: smaller inner thighs, flatter abdomens, and more toned arms,[12] while also being concerned about becoming too bulky.

[13] She also started training her sister's friends who wanted to improve their fitness so they could play Netball on their high school team,[5][14] focusing on building core strength and powerful legs.

[20] In November 2016, Pan Macmillan published Itsines' first print book, The Bikini Body 28-Day Eating and Lifestyle Guide.

[12] Part of her social media strategy is to keep attention on the transformation of the body, and she therefore seldom posts photos of her face.

[5][18] In a statement of her own values, she says she would never promote something in which she personally does not believe, pose provocatively or sexualise herself, or post advice that is relevant only to her own lifestyle.

[26] In October 2016, Itsines and her then partner, Tobi Pearce, were included in the BRW "Young Rich" list of the wealthiest Australians aged under 40 who had not inherited their money.

[27] Itsines and Pearce's net worth was estimated as A$486 million on the Financial Review 2019 Rich List.

[28] Itsines' net worth did not meet the A$472 million cut-off for the Financial Review 2020 Rich List.