There is debate among professionals regarding the use of the glycemic index (GI) for meal planning. In type-1 diabetes, there are 4 studies (average duration ~4 weeks) comparing high versus low GI diets; none reported improvements in HbA1c, and although 2 reported improvements in fructosamine, 2 reported no differences. In type-2 diabetes, there are 12 studies (average duration ~5 weeks); 3 reported improvements in HbAlc and fructosamine, 5 reported no differences in HBA1c, and 3 reported no differences in fructosamine. In adults, there is limited evidence that a low GI diet is beneficial for weight loss or satiety. Three epidemiologic studies reported that a low GI/glycemic load (GL) is associated with a reduced risk of developing diabetes or prevalence of insulin resistance; however, 5 studies report no association between GI/GL and the risk of developing diabetes, fasting insulin or insulin resistance, or adiposity. In general, the total amount of carbohydrate in a meal is the primary meal-planning strategy for people with diabetes. The GI can be used as an adjunct for the fine tuning of postprandial blood glucose responses. Other food/meal-planning interventions have been shown to be more effective than the use of the GI.
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Carbohydrates can be classified based on their chemical structure and/or based on their physiological effects. Based on chemical structure the major dietary carbohydrate groups are: sugars, starch, and fiber. Defining carbohydrates by chemical structure, however, does not take into account their physiologically differing responses, such as differences in satiety value, gastric emptying times, and effects on glucose and insulin levels. To better define physiological responses, the concept of a glycemic index (GI) was developed by David Jenkins and colleagues in the 1970s. The GI is defined as the relative area under the postprandial glucose curve comparing 50 g of digestible carbohydrate from a test food to 50 g of carbohydrate ingested from 50 g of a standard food - pure glucose or white bread. As defined, the GI takes into account only the type of carbohydrate in food and ignores the total amount of carbohydrate in a typical food serving, although both the type and amount of carbohydrate influence the postprandial and insulin responses of a given ingested food . In an attempt to compare the glucose-raising effect of foods with their widely differing amounts of carbohydrate, the glycemic load (GL) was developed. The GL is defined as the GI multiplied by the grams of carbohydrate in a specific portion of a carbohydrate-containing food or meal. For example, although carrots have a high GI, because they contain relatively small amounts of carbohydrate they have a low GL.
Perhaps the most widely held belief in regard to carbohydrates and diabetes has been the assumption that the response to food carbohydrates was based on the chemical composition, e.g. sugars versus starches. However, about 20 studies have reported that when subjects are allowed to choose from a variety of starches and sugars, the glycemic response is identical as long as the total amount of carbohydrate is kept constant . Therefore, the American Diabetes Association concluded that with regard to the effects of carbohydrate on glucose concentrations, the total amount of carbohydrate in meals and snacks is a key strategy .
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