What Are the Effects of Cooking and Ripening on Glycemic Index?
In most cases, the cooking method affects the glycemic index of a food. For example, fried foods usually have a high level of fat that may reduce the absorption of sugar in the blood and reduce the GI. Studies show that baking and roasting can break down resistant starch, a type of starch that slows down digestion and is commonly found in foods such as legumes, oats, and potatoes, thus elevating the glycemic index. Boiling helps preserve more of the resistant starch and cause low glycemic index. When you cook foods such as rice or pasta for a long time, the starch content becomes easier to digest and the glycemic index increases. This is why it is advisable to cook these foods until they get to an Al dente texture, which is they should still be firm when you’re biting into them.
The extent of ripeness of a food may also affect the glycemic index of some fruits, such as bananas. This is because the amount of resistant starch reduces during the ripening process, causing a higher glycemic index. For instance, bananas that are completely ripened usually have a glycemic index of 51. Under-ripe bananas on the other hand may have a GI of 30.