We don’t know yet the actual, long term damages. Maybe this is like leaded gasoline - very bad for everyone, but it takes long term accumulation to really show the effect.
We have a meme in Europe that a visit to the US means you will gain a few pounds of extra body fat that’s harder to lose than usual. That’s just anecdotal, of course. But as a result, my suspicion is that dietary compounds (mainly HFCS) are the culprit.
Generally my experience as well. Working in Asia and Australia I lost weight, and then ballooned when I got back to the US. Especially noticeable when I got back to the East Coast.
HFCS is sugar, yes, an especially unhealthy form. Probably pushed for political/economical reasons in the US because it can be made domestically from corn, it’s way less prevalent in other areas. Eg in Germany, it has to be declared as glucose-fructose-syrup starting at 5% fructose, and as fructose-glucose-syrup starting at 50% fructose. The overwhelming majority of products I‘ve encountered contains just „glucose-syrup“ or plain sugar (usually from sugar beet, which is grown domestically).
Fructose is ok to consume in amounts that are typical for fruit (which is less than you‘d think), but is a metabolic disruptor in higher amounts. Liver cells have to do a lot of work to metabolize fructose, compared to glucose which needs quasi no conversion. As to health effects of fructose, I‘ve found it hard to determine which studies are reliable, because there is just so much money in this industry, and high interest to influence research. But the metabolic complexity it brings is undeniable, and one could argue that fructose is kinda like a poison we have adapted to - if we lack key enzymes, we can’t metabolize it.
Glucose is harder on the pancreas and chronic high insulin seems to be really bad, so I‘d avoid that too of course. But a reasonably healthy liver can quickly buffer excess glucose (hepatocytes) and rather easily convert to glycogen and store it, in big amounts.
