All non-fibre carbohydrates are metabolized as sugar, and it's VERY rare for our bodies to convert carbs into fat. All complex sugars are broken down into monosaccharides before absorption. Chew on a piece of bread for a couple minutes and enzymes in your saliva will break it down into glucose, and it will become sweet in your mouth.
Dextrose is glucose, and sugar does not directly make you fat. Eating a sustained caloric surplus makes you fat, no matter the macronutrient composition of your diet.
Here's more detail about the biochemistry of how we get fat - http://www.bodyrecomposition.com/fat-loss/how-we-get-fat.htm...