How does one identify gushers and tricklers? Several factors affect the digestibility of a carbohydrate and its GI value. The most important GI determinant is the physical state of the starch. The development of grinding, milling, and other food processing techniques over the past 200 years has had the greatest impact on the quality of the carbohydrates in our current diet. Removing outer fibrous layers and reducing the particle size of grains such as wheat enhances quick digestion. This is why breads, crackers and other bakery products made from finely milled enriched flours have high GI values, while stoneground products that are dense and grainy have lower GI values.
Along with milling and the like, simply cooking in water can have a big impact on the physical state of a starch. The longer a starch is exposed to water, the more gelatinized its particles, the more swollen it becomes, and the faster it turns into glucose. Thus, overcooking any type of pasta, for example, will increase its GI value. The presence of soluble fiber (rolled oats, beans, lentils, apples), acids (sourdough bread, pickled vegetables), and fat and protein are all factors that slow digestion and release glucose more slowly into the blood.