The X Factor judge made a commitment to changing his lifestyle after a health scare in 2017.
Simon fell down the stairs at his London home after suffering low blood pressure.
In a dramatic diet change, Simon has converted to veganism and cut out several foods.
Speaking to Extra TV, he revealed he has cut out red meat, dairy, sugar, bread and gluten after being advised to do so by a specialist.
Simon Cowell weight loss: How X Factor judge dropped 20lbs by swapping diets.
He was also advised to reduce his alcohol consumption, which had been his biggest worry to begin with.
Simon explained the doctor had said to not drink “quite as much as you had before”.
Simon, who is worth around £494million, continued “I did it and I stuck to it and it’s easy”.
He went on to explain how he is on the “Eric Cowell diet.”
Eric, who is his five-year-old son, likes ice cream, water, and “eats all his raw vegetables”.
In the interview, he also said: “I went to see this guy who’s very well-known.
“And he said to me, after doing some blood work, ‘You can’t have red meat, dairy, sugar, bread or gluten.”
Simon decided to cut out the stuff he “shouldn’t have been eating”.
The music mogul used to binge on sausage rolls, hamburgers and his favourite jam tarts, according to The Sun.