Factors that affect the GI index of a food
1. Degree of Gelatinization
The more gelatinized (swollen) the food, the higher the GI. With cooking the starch swells and the enzymes in the small intestines have a greater surface area to digest the carbohydrate.
2. Particle Size
Industrialization has changed our diet. Our ancestors ate carbohydrates in the form of beans, vegetables, fruits and whole grains. They ground the food between stones and cooked it over heat, and the fibre was still intact. As a result, the carbohydrates eaten were digested and absorbed slowly resulting in a low glycemic response in the blood.
Today, we eat new foods based on these whole grains – but the original grain has been ground down to produce fine flours of small particle size that produce fine-quality breads, cakes, cookies, crackers, pastries, cereals and snack foods. Our bodies quickly digest and absorb these “refined” carbohydrates resulting in a high blood-glucose and insulin response.
3. Physical Form of Food
Fibre will slow down the digestion of the food, thus resulting in a slower rise of blood glucose. The fibrous coat around beans also acts as a physical barrier and slows down the digestion of the carbohydrate inside the bean.
4. Amylose to amylopectin ratio
There are two sorts of starch in foods- amylase and amylopectin.
Amylose is a straight-chain molecule. It is harder to gelatinize and therefore harder to digest. Amylopectin, on the other hand, consists of a string of molecules that have several branching points and are larger and easier to gelatinize and digest.
Some rice like Jasmine rice have a high GI because of the high amylopectin content, while Basmati rice with a higher amylose content has a low GI. In general, the more sticky the rice, the more gelatinized the starch, the higher the GI value.
