And, here in the U.S., it is an extremely old problem. The United States had a higher obesity rate in 1970 (before HFCS was introduced) than countries like Spain or France have today.
I try to consume as little HFCS or sugar as possible, and I don’t think that one is necessarily better than the other.
The real cause, I think, is restaurants (including, but not limited to fast-food) and their drive to make bigger and tastier portions. The way our human bodies work, it’s easy to gain weight by overeating, it’s very hard to lose it. You can gain 1/3 to 1/2 lb. without thinking twice just by eating once at El Torito or Chipotle, unless you exercise conscious restraint and stop halfway through the meal. Once that fat is in your body, it’s going to stay there, it takes a lot of strenuous exercise, something like 2 hours on a treadmill, to get it out. Go to El Torito once a week for three years without exercising – that’s 60 lbs, enough to get you from normal BMI to obesity. Since most people go to restaurants much more often than they exercise for 2 hours continuously, it’s no surprise that so many people are fat.