Post-meal blood sugar control depends on proper insulin timing
By Gary Scheiner MS, CDE
Postprandial hyperglycemia refers to a high blood sugar spike that occurs soon after eating a meal or snack. For everyone with Type-1 or Type-2 diabetes, it is natural for the blood sugar to rise after eating. But if the rise is very dramatic, if can effect a person’s well-being and quality of life.
Even though the spikes are temporary, all those after-meal rises can result in a higher HbA1c than your patients’ pre-meal readings would indicate. In fact, research reported at the ADA scientific sessions indicated that the average blood sugars during the three hours after eating, not before, correlates most closely to HbA1c levels.
Research on the effects of postprandial hyperglycemia has also shown an increase in the risk of death from heart disease in those with Type-2 diabetes, earlier onset of kidney disease, and accelerated progression of retinopathy in those with Type-1. There is growing concern that blood glucose variability, and not just a high average, contributes to microvascular disease.
And then there are the acute effects. As most anyone with diabetes will attest, blood sugar spikes have been shown to negatively influence mental concentration, energy levels, mood, and physical performance.
In most cases, blood sugar levels peak about an hour after finishing a meal or snack. Ideally, the blood sugar at the peak should be below 180 mg/dl in adults (160 during pregnancy). Less stringent targets may be used in higher-risk individuals: 200 in adolescents and adults with hypoglycemia unawareness or high-risk jobs, 225 in school-age children and 250 in very young children. Perhaps the most practical is to check the blood sugar level about one hour after eating with a home blood glucose monitor (using capillary blood from a finger rather than an alternate site). Continuous glucose monitors are another excellent way to see exactly how much the blood sugar levels are rising after meals and snacks.
Reducing after-meal spikes does not usually require taking more insulin at mealtimes. In fact, if your pre-meal readings are already close to normal, increasing your insulin would probably result in hypoglycemia before the next meal.
Reducing the magnitude of the spike while maintaining near-normal pre-meal readings can be accomplished in a number of ways. Choosing lower-glycemic-index foods — foods which cause a more gradual rise in blood glucose levels — is certainly an option. Engaging in light-to-moderate physical activity right after eating will also help, as will injections of pramlintide (Symlin) prior to each meal. But one simple, often-overlooked answer is to simply take your mealtime insulin earlier.
The timing of your mealtime insulin (boluses) can significantly impact your after-meal spikes. Boluses given too late to match the digestion of carbohydrates can produce significant hyperglycemia soon after eating, whereas a properly timed bolus can result in excellent after-meal control.
Let’s first assume that you are using a rapid-acting insulin analog (Humalog, Novolog or Apidra) for your mealtime boluses. If you are unlucky enough to be using Regular insulin, either by itself or premixed with NPH, take all the advice given below and back everything up by 20-30 minutes. Let’s also assume 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 the blood sugar, and usually require that boluses be administered after food has been consumed. Otherwise…
The majority of simple and complex carbohydrates commonly consumed, including cereal, bread, potatoes, rice and snack chips, have a high glycemic index value. They digest and absorb into the bloodstream quickly, resulting in a blood sugar peak in 30-60 minutes. For these types of foods, it is best to give your mealtime insulin bolus 15-30 minutes prior to eating. This will allow the insulin peak to coincide as closely as possible with the blood sugar peak. And that, of course, will produce the best possible after-meal control. Bolusing for high-GI foods immediately before or while you are eating will cause an after-meal “spike,” as the insulin peak would lag behind the blood sugar peak by almost half an hour.
If you are not certain of how much food you are going to consume at the meal, it is best to make a “down payment:” bolus ahead of time for an amount that you are almost certain to eat. Then, after the meal, do the “accounting” figure out how much you went above your pre-meal estimate, and bolus for the balance. For those who use an insulin pump, taking a couple of boluses for each meal should not be a major inconvenience. For those on injections, it might be beneficial to utilize an insulin pen or indwelling infusion port (I-Port or Insulflon), or consider making the move to a pump.
Does earlier bolusing make a difference? Research published in 2004 showed an average post-meal “spike” reduction of 50mg/dl simply by blousing 15 minutes pre-meal. From my own experience, it makes an even greater difference…particularly when the pre-meal blood glucose level is taken into account. Delaying the meal an extra 10-15 minutes when the blood glucose is above target gives the insulin a chance to start lowering the blood sugar before the meal kicks in. Conversely, if the pre-meal blood sugar is low (or close to it), it is best not to give the bolus more than a few minutes before the meal. This will help in preventing a significant insulin reaction before the food kicks in.
One other key point to remember: the pre-meal bolus will only work well on food works faster than insulin. Some carbohydrate-containing foods have low glycemic index scores (such as pasta, milk, yogurt and beans). These types of foods will digest gradually, and do not tend to cause a dramatic post-meal blood sugar spike. When consuming these types of foods, bolusing just prior to eating should suffice.