Yes, certain foods and how they are cooked can affect the Glycaemic Index. Fat and fibre content tend to lower the Glycaemic Index (GI) of a food item. As a rule, the more cooked or processed a food, the higher the GI.  Factors that affect the GI of a food item include the following. Ripeness and storage time: The riper a fruit or vegetable is, the higher the GI. Processing: Juice is higher in GI than whole fruit; mashed potato is higher in GI than whole baked potato; stone-ground whole-wheat bread is lower in GI than whole wheat bread. Cooking method: When compared to other cooking methods, boiling is thought to help retain more of the resistant starch and result in a lower GI. The longer you cook foods like pasta or rice, the more digestible the starch content becomes, and thus the higher GI value. Variety: Short-grain white rice has a higher GI than brown rice but converted long-grain white rice has a lower GI than brown rice.