Yes, the diet Elvis Presley chose to partake ultimately led to his demise. He put on more and more weight in his later life and was no longer the svelte movie star so many women and girls swooned over in the earlier years of his career. If he would have had a healthier diet, he would not have died as soon as he did.
Elvis Presley had an exaggerated idea of his own capabilities. He lived a life of luxury and never had to deny himself any urge or want. These two things lead to him eating a ridiculously unhealthy diet throughout his entire life. When he did face stress and pressure to perform, comfort foods were his coping mechanism.
If Presley died of colon issues, then his diet most certainly had something to do with it. Being backed up with bile is not healthy for any person ever. Celebrities have to remember to eat their fruits and vegetables and get the right amount of water in their systems. Eating unhealthy food can be healthy when they are on the road, but they must stop.
Did Elvis' diet contribute to his death? Well, I would say no unless that diet consisted of narcotics, heroin and other prescription pills. Elvis was a very sick man whose condition was exacerbated by drug use. He lived a great life of privilege and did it his way so you can't really feel sorry for him and no I don't blame his diet for his demise.