Is there a correlation between the obesity, diabetes problems, and the switch to corn syrup as a sweetener?

Yes: High fructose corn syrup is a major contributor to diabetes and obesity& is used as a sweetener in many commercially available products. It raises the blood sugar significantly up increasing the level of Insulin & lipoprotein lipase (a fat depositing enzyme) which causes the body to deposit fat, especially in the abdominal area rather than use it as energy and it leads to weight gain and diabetes.