There are 3 main types of carbohydrates;

Mono-saccharides which contains one sugar molecule.  Examples include dextrose (GI 100) and fructose (GI 19).

Di-saccharides which contain two sugar molecules.  Examples include sucrose (GI 65), lactose (GI 45) and maltose (GI 105).

Poly-saccharides which contain many sugar molecules.  Examples include wheat, oat (GI 55), barley (GI 25) and potatoes (GI 82).

Used as a currency to evaluate the effect on the body’s blood glucose levels, the Glycaemic Index (GI) measures the effect of 50 g of carbohydrate found in a particular food on insulin levels.  If the measure is high (above 55), it is held that the body will experience spiked blood glucose levels which in turn through insulin release will be deposited to fat cells.  What the GI score doesn’t indicate is how relatively dense in carbohydrate the food naturally is.  Some fruits and vegetables have a high GI score but contain large proportions of fibre which means consuming the 50 g used in the score would be very difficult.

Similarly, fructose which appears with a GI score of only 19 would appear to have very little effect on blood glucose levels.  However, its primary response is on blood fructose levels which is far worse for the body.

Put simply, the more complex, natural and fibre bound the carbohydrate source is, the better, unless for instance an insulin spike is required to aid the uptake of protein in a post workout scenario.