In Michael P Ghiglieri and Thomas M. Myers's book Over the Edge: Death in Grand Canyon (a chronicle of deaths in the Grand Canyon by a biologist and a medical doctor), in the section about squirrels biting humans who are feeding them, it is mentioned in passing that,
Due to their penchant for successfully duping then intimidating tourists, the chubby little guys actually become unhealthy. Like many of the humans feeding them, the squirrels too die younger from heart disease, cancer and other problems relating to obesity.
However, there are no references to back it up.
Are there any scientific studies showing a link between human food and squirrels getting cancer/heart disease?