Rice varieties with similar amylose content differ in starch digestibility and glycemic response in humans

Article Abstract:

Different types of starchy foods are digested at different rates and have differing effects on blood glucose and insulin levels. Starches that are digested quickly cause a rapid increase in the amount of sugar in the blood, while those that are digested more slowly do not cause such rapid changes in blood sugar levels. Eating foods that are digested slowly and do not cause a rapid rise in blood sugar is important for people with diabetes, because they have trouble controlling the amount of sugar in their blood. Starch contains amylose, which is structurally a long string of glucose molecules bound together. It has been reported that as the amount of amylose in the starch increases, the starch will swell less (gelatinize) during cooking and will be digested more slowly. Therefore, people with diabetes have been told to eat foods that are rich in amylose. However, some studies have reported that starch rich in amylose is digested at the same rate or faster than starch with little amylose. To investigate the relationship between starch digestibility and blood glucose levels, the blood glucose response to three different types of rice, which is rich in amylose, was determined in 11 healthy volunteers. All three types of rice contained the same amount of amylose, but they differed in the rate at which they were digested. The rate of digestion and blood sugar levels were related to the length of cooking time, the amount of swelling and the consistency of the rice. When all three types of rice were cooked to the same consistency and amount of swelling, the rate of digestion was the same. It is concluded that the amount of amylose present in starch is not a good predictor of digestibility. Starches with similar amounts of amylose may differ in their degree of swelling and minimum cooking time, and this can influence the rate of digestion and blood sugar levels. Starches that have the least amount of swelling during cooking are more likely to be digested slowly. (Consumer Summary produced by Reliance Medical Information, Inc.)

Starch, Control, Rice, Digestion

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Glycemic response and fiber content of some foods

Article Abstract:

Dietary fiber (DF) is thought to lower the glycemic response, the rise in blood glucose levels following eating, experienced by diabetics. A number of different mechanisms by which DF moderates this response have been proposed, most involving retarding some aspect of the digestive process such as rate of digestion of starch, rate of motility of foods from stomach to intestine, or rate of absorption of sugars (broken down from starch or other carbohydrate) from intestine into the bloodstream. Of five proposed mechanisms, three would not be linearly dependent on levels of DF, that is, the observed change would not increase in proportion to increases in DF levels. If an equation relating levels of DF to the glycemic index (GI, an indicator of the relative rise in blood sugar following meals) could be calculated, it would be useful in evaluating glycemic responses to foods with unknown GIs. The relationship between total dietary fiber (TDF), which is comprised of soluble DF (SDF, found in oats, beans, barley, and prunes, for example) and insoluble DF (IDF, found in wheat bran, for example) was investigated, and effects of other factors such as food processing, cooking, other food components, and the chemical nature of starches were considered. An empirical equation was derived, with a theoretical basis for the relationship not yet explained. In this equation, the GI response was equal to the -0.322 power of DF times 19.9, or ln GI=ln 19.9 + -0.322 ln DF. Similar equations were constructed to relate GI to SDF and to IDF. SDF had an appreciably greater effect on GI than did IDF. The study suggests that the content of total DF of a food is useful in predicting the food's GI, but more investigation of effects of the types of DF is needed. (Consumer Summary produced by Reliance Medical Information, Inc.)

Fiber in human nutrition, Dietary fiber

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