Italian brand Nutella, a sweetened hazelnut cocoa spread, sponsored the Spanish giants at the time when the then 23-year-old Cassano moved to Madrid from Roma in January 2006.
"When I arrived at Real Madrid, I lost 12 kilos immediately," Cassano said in a conversation with former Italy teammates including Christian Vieri and Fabio Cannavaro.
"Then I gained them back. Nutella was one of the club sponsors and each month they would give us five kilograms of the product."
Considered one of the most promising forwards of his time, Cassano failed to shine at Madrid under his former Roma coach Fabio Capello and left after 19 months to join Sampdoria.
"When Capello arrived [summer of 2006], I scored two goals in two games and I felt like I was the king of the world," Cassano added.
"He replaced me in the first half against Lyon, I had an argument with him in Jerez and he withdrew me from the team. In seven months, I gained 14 kilos, I ate Nutella directly from the jar and I couldn't care about anything. I was disgusting."
Cassano, 38, had weight problems throughout his career and admitted his lavish lifestyle in Madrid damaged his playing prospects.
"My biggest mistake was the year-and-a-half at Real Madrid, because I did everything and more to ruin it," he said. "That's a huge regret."