The Mexican-American pulled off one of the biggest shocks in boxing history when he knocked out Joshua to win the IBF, WBA, WBO and IBO titles back in June.
But Ruiz raised eyebrows when he weighed in 15 pounds heavier for the second fight – a remarkable three stones heavier than Joshua.
The Briton subsequently danced around a plodding Ruiz to win back his titles, leaving the former heavyweight champion of the world to dwell on where it all went wrong.
And Ruiz has concluded his problems may have started in the kitchen.
Speaking to TMZ Sports, Ruiz confessed: “I think I ate everything. Everything. That is why I gained so much weight.
“I was having too much fun, I was celebrating too much. Just being with my friends and just celebrating. Drinking a few more Coronas than I should have.
“Even out of shape, even the way that I was training back and forth … f***, I did pretty good. I did pretty good!
“But I wish I had taken it more serious.”
“For the third fight, I’m going to give it all I got. I want those belts back!”
But Ruiz may be made to wait for his chance. Joshua has been ordered to fight Oleksandr Usyk in the next 180 days by the WBO, while the Bulgarian Kubrat Pulev is his IBF mandatory.
So Ruiz would be well advised to lay off the Coronas in the meantime.