Not all Carbohydrate foods are equal. The Glycemic Index (GI) is a relative ranking of carbohydrate in foods according to how they affect blood glucose levels.Carbohydrates with a low GI value (55 or less) are more slowly digested, absorbed and metabolised and cause a lower and slower rise in blood glucose and, therefore insulin levels.ï»¿ot all Carbohydrate foods are equal. The Glycemic Index (GI) is a relative ranking of carbohydrate in foods according to how they affect blood glucose levels.