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I just saw a chart comparing the % calories from various food sources from 1982 to 2012. Grain didn't change, but sugar did. So "carb" has to be differentiated between glucose and fructose. I think in these countries quality glucose carbs like rice have been replaced with white flour products (higher insulin spike), and massively more amounts of sugar (specifically fructose).
I believe the stat was we are designed and adapted to handle 12-24g of fructose a day (a few raw fruits), but the average now is 80g (without the other benefits of fruit - fiber, vitamins, slower to digest, more diluted), with some well over 100g or 25% of daily calories from fructose!
Another thing to consider with fructose is that the metabolic fate of fructose depends, in part, on carbohydrate balance. Most fructose is taken up by the liver (due to high affinity receptors). If you are in a positive carbohydrate balance (either due to high carb or low activity, or both), the liver coverts the fructose to triglycerides and packages them for export in VLDL cholesterol particles (which become LDL).
However, if your liver glycogen levels are not full (either due to low carb or high activity), your liver converts the fructose to glycogen with no ill effects.
So, you can handle more fructose with no ill effects if you are more active, or if your other carbohydrate (besides fructose) consumption is lower.