Fitness entrepreneur Kayla Itsines announced Tuesday that she has been diagnosed with the Epstein-Barr virus (EBV), a condition that can cause chronic fatigue and fever, following a period of severe burnout. Itsines, 35, shared the news on social media, explaining that the diagnosis clarified recent struggles with extreme brain fog and fatigue.
"Two months ago I was really struggling with extreme brain fog and fatigue. I went to the doctor's; it came back positive for EBV, which makes a lot of sense," Itsines said. She added that her doctor advised her to slow down and regulate her nervous system.
The diagnosis came as a shock to Itsines, who built her career around an active lifestyle and a perfectionist mindset. "As a high-performing perfectionist, there is no slowing down for me," she stated.
Itsines first gained prominence over a decade ago with her Bikini Body Guide e-book, which evolved into the Sweat fitness platform. She co-founded Sweat with her ex-fiancé Tobi Pearce. In 2021, she sold Sweat to US fitness company iFIT for a reported $400 million, later repurchasing it in 2023 for a lower price.
In 2025, Itsines was listed at number 40 on the Australian Financial Review Young Rich List, with her fitness empire valued at $176 million. She was ranked 34th on the same list in 2024, placing her just behind actress Margot Robbie.
Earlier this year, Itsines also shared details about her meticulous hygiene routine, describing how she would restart the process if distracted. "I don't want to say OCD without getting properly diagnosed, but I won't leave the shower if I don't brush my teeth twice, wash my face twice and wash my body in a certain order," she wrote on Instagram in December.