Barone, who worked with Ronaldo during the forward's time at Juventus, made the disclosure in an interview with Covers.com.
"No milk. Humans are the only animals that drink the milk of other animals. No other animal drinks milk after three months. It does not exist in nature. Only human beings continue to drink milk up to 30, 40, 50 and 60 years, and in my view it is wrong. After infancy it is not normal. It is against nature," Barone told covers.com.
The Al-Nassr striker, 41, follows a strict nutritional programme built around lean proteins, healthy fats and vegetables, eating six small high-protein meals per day and avoiding sugar, flour-based products and soft drinks.
Barone described a typical day's eating: "Starting with breakfast, he would have an avocado with coffee, eggs and no sugar. Absolutely no sugar. Lunch could be chicken, fish and always vegetables. In the evening, he eats light foods, usually fish or meat in the form of fillet. It's always accompanied by vegetables."
His favourite meal is Bacalhau à Brás, the traditional Portuguese dish of scrambled eggs, salted cod and fried potatoes.
Ronaldo's stance on milk contrasts with that of Erling Haaland, who has spoken publicly about drinking raw milk. Barone stopped short of criticising the Manchester City forward on all points: "I agree with eating the organs. The liver, heart and brain are all healthy foods. They are superfoods. Cristiano liked liver too. But not for the milk."
Ronaldo's body fat is reported to sit at seven per cent — below the eight to twelve per cent typical for Premier League players.