Look at the biochemistry metabolism chart I posted a link to. Each dot on there is an enzymatic reaction taking it all around in a big circle.
It is not JUST high carbohydrates that is the problem - it is high protein, high fat, high sugar AND high carbohydrates that is typical of the American diet.
This is the fact: if you take in more calories (from fat, from sugar, from carbs, from protein) than you burn - your body will turn that extra energy into lipids and store it as fat.
There is no exemption if the excess calories were from fat and protein then your body doesn't “know” how to deposit the excess as fat.
The molecular enzymes “know” how to turn excess calories from fat and protein into adipose tissue just fine.