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“Just as calories differ according to how they affect the body, so too do carbohydrates. All carbohydrates break down into sugar, but the rate at which this occurs in the digestive tract varies tremendously from food to food. This difference forms the basis for the glycemic index (GI). The GI ranks carbohydrate-containing foods according to how they affect blood glucose, from 0 (no affect at all) to 100 (equal to glucose). Gram for gram, most starchy foods raise blood glucose to very high levels and therefore have high GI values. In fact, highly processed grain products – like white bread, white rice, and prepared breakfast cereals – and the modern white potato digest so quickly that their GI ratings are even greater than table sugar (sucrose). So for breakfast, you could have a bowl of cornflakes with no added sugar, or a bowl of sugar with no added cornflakes. They would taste different but, below the neck, act more or less the same. A related concept is the glycemic load (GL), which accounts for the different carbohydrate content of foods typically consumed. Watermelon has a high GI, but relatively little carbohydrate in a standard serving, producing a moderate GL. In contrast, white potato has a high GI and lots of carbohydrate in a serving, producing a high GL. If this sounds a bit complicated, think of GI as describing how foods rank in a laboratory setting, whereas GL as applying more directly to a real-life setting. Research has shown that the GL reliably predicts, to within about 90 percent, how blood glucose will change after an actual meal – much better than simply counting carbohydrates as people with diabetes have been taught to do.” — David Ludwig