In an interview with Extra, the X-Factor judge said he feels 'much better' since changing his diet, and had lost 'around 20lb' doing so.
He also said that while pizza was his biggest craving - he doesn't allow himself to stray from his diet and 'have a cheat day'.
When the star announced his drastic dietary change to The Sun, he said he will 'soon give up fish'.
It hasn't yet been confirmed whether Cowell has fully committed to a plant-based diet yet.
'The word diet makes me miserable'
He also told The Sun his new diet had made him more handsome - saying 'I was an eight [out of 10] and now I've gone to an 11' and described the benefits he'd already noticed.
"I have more energy and focus and it wasn't difficult. I don't like to use the word diet because that's the reason I never went on a diet before - the word diet makes me miserable," Cowell added.