So...lore-wise, he had his first stroke on the way to a Las Vegas trip. He attributes the stroke to him drinking Red Bulls, saying that the guarana and taurine combination was what caused it, and not his wildly unhealthy eating habits and tendency to slam down cans of energy drinks regularly.
BTW: Scientists confirmed that it was the excessive caffeine content as well as co-morbitities like high blood pressure (of which Jack does have) that leads to strokes.
Jack also says he drinks Bangs now because they're "sugar free", but fails to understand that they contain nearly 3x the caffeine of a regular Red Bull...tick tock, Fatty Doo Doo.