Another class of diabetes medicines called alpha-glucosidase inhibitors improve after-meal control by partially blocking the transport of some carbohydrates across the intestines and into the bloodstream. However, these drugs can sometimes cause temporary gas, bloating, and gastrointestinal upset. You might recall that physical activity after meals will also slow the movement of carbohydrates into the bloodstream, but without the side effects!
Back up your bolus. In the real world, the fourth dimension (time) is of the essence. The timing of your mealtime insulin doses (often called boluses) can significantly affect how high your blood glucose level rises after meals. Boluses given too late to match the digestion of most carbohydrates can result in significantly high blood glucose soon after eating. However, a properly timed bolus can result in excellent after-meal control.
The advice presented here assumes that you are using either lispro or aspart for your mealtime boluses. If you use Regular insulin, either by itself or premixed with NPH, take all the advice given below and back everything up by 20–30 minutes. It is also assumed that you do not have a condition that impairs your digestion, such as gastroparesis (a nerve disorder that slows emptying of the stomach) or gastritis (nausea and upset stomach). These conditions can significantly delay the rate at which carbohydrates raise blood glucose level, and they usually require that boluses be administered after food has been consumed.
Foods with a high glycemic index (greater than 70), such as cold cereals, bread, potatoes, rice, and snack chips, tend to raise blood glucose the fastest, with a significant peak occurring in 30–60 minutes. For these types of foods, it is best to bolus 15–20 minutes prior to eating. This will allow the insulin peak to coincide as closely as possible with the blood glucose peak. And that, of course, will produce the best possible after-meal control. Bolusing for high-GI foods as you are eating them will cause an after-meal spike, because the insulin action will lag behind the blood glucose rise by almost half an hour.
Foods with a moderate glycemic index (approximately 45–70) digest a bit slower, resulting in a slightly less pronounced blood glucose peak approximately 60–90 minutes after eating. Examples include ice cream, orange juice, cake, and carrots. It is best to bolus immediately prior to eating foods with a moderate GI. This will allow the insulin peak to closely match carbohydrate digestion and result in the best possible after-meal control.
Foods with a low glycemic index (below 45) tend to cause a slow, gradual blood glucose rise. The blood glucose peak is usually modest and may take several hours to appear. Examples of foods with a low glycemic index include pasta, milk, yogurt, and kidney beans. For these types of foods, a few bolus options are available. One option is to bolus 10–15 minutes after finishing your main course. This usually gives the food enough of a head start before the insulin kicks in. A second option is to split the bolus into two or three parts and to take each about an hour apart, starting at the mealtime. A third option is to take Regular insulin with the meal, rather than a rapid-acting insulin analog. One other option, available to users of insulin pumps, is to extend the bolus delivery over an hour or two.
Another variable to consider when determining the timing of your mealtime bolus is your premeal blood glucose level. To avoid an after-meal drop or spike in your blood glucose level, it is best to give the bolus earlier when your blood glucose is elevated and later when it is below your target. The chart “Bolus Timing in Relation to Meals” combines the glycemic index and premeal blood glucose level to determine optimal bolus timing.