Is high fructose corn syrup unhealthy?

Depends who's asking: I have done quite a bit of reading on this. Studies in mice show metabolic syndrome (middle-age man syndrome) can be induced with high fructose diets and reversed when it is removed. This is not true of glucose or sucrose. See the article: "research offers insight to how fructose causes obesity and other illness" sciencedaily (feb. 27, 2012) or am j physiol renal physiol. 2006 mar;290(3):f625-31.

Obesity, pain: Humans have a limit to how much fructose the bowel can absorb at any given time. If you max out this limit, the fructose stays in the bowel and causes pain, bloating, and diarrhea. This is not dangerous, however. Just uncomfortable. The real health problem with hfcs is that because of its sugar contents, it is a major contributor to obesity and its consequences such as type ii diabetes.

Calories: In and of itself its just a kind of sugar, but foods high in fructose tend to have a lot of calories, thus may promote obesity. There is very controversial theories that suggest fructose may affect hormones involved in appetite regulation ( like leptin) and promote obesity in that fashion as well, but direct and definite proof is not yet out there at this time.

Obesity, pain: Humans have a limit to how much fructose the bowel can absorb at any given time. If you max out this limit, the fructose stays in the bowel and causes pain, bloating, and diarrhea. This is not dangerous, however. Just uncomfortable. The real health problem with hfcs is that because of its sugar contents, it is a major contributor to obesity and its consequences such as type ii diabetes.