Hi,
Its eating carbs that are LOW GLYCAEMIC in other words low in sugars, as the more high sugar carbs you eat the more (if you have a tendency towards it) you`ll store fat! Thats it in simple terms.... google it hun and that will explain it better than ickle old me! Lol Patric holford has been around for a long while and there are many other low GI ( Glycaemic index) or now better version called GL (Glycameic Load)
Here is an excerpt from another page...
The Glycemic Index (GI) has been used for many years as  guide to the rate at which carbohydrate content is absorbed into the  blood stream for energy, and the effect it has on raising blood sugar  levels. The Glycemic Index (GI) is a measure of the degree to which a  carbohydrate is likely to raise your blood sugar (glucose) levels.  The  scale is 0 to 100 (based on either white bread or glucose), with 0 being  low and 100 being high.  The GI compares equal quantities of  carbohydrates and provides a measure of carbohydrate quality 
but not quantity. So the drawback with GI ratings is that they are not based on commonly-consumed portion sizes of foods. 
 
For example, only about 7% of a carrot is made up of are useable  carbohydrates. But because a 50g carbohydrate content is employed as the  standard measure for a GI rating of individual foods to show how fast  blood sugar level are raised, a larger than normal food portion is used  for the GI calculation.  In the case of carrots, for example, the amount  is equivalent to 1.5lbs - far more, of course, than people normally eat  as a snack or part of a meal. 
 
As a result, the GI rating often overstates relatively small carbohydrate content in a food item like a carrot. 
 
The reverse is also true, i.e. the glycemic effects of foods containing a  high percentage of carbs like bread, can often be understated under the  GI system.
 
Therefore we recommend using the Glycemic Load index with calculations  based upon realistic food portions. GL ranks food according to the  effects of actual carbohydrate content in a standard serving size of  food.
Hope that helps a little bit 
