Updated June 06, 2005

Rapid-Acting Insulin
Timing It Just Right

by Hope Warshaw, M.M.Sc., R.D., B.C.-A.D.M., C.D.E.

In general, foods and combinations of foods that have a low glycemic index and high fiber content will raise blood glucose more slowly. Meals and snacks that have a higher glycemic index and are lower in fiber will raise blood glucose more quickly. Meals and snacks that are high in fat content tend to cause a delayed rise in blood glucose.

The extent to which the glycemic index or fat content of a meal speeds or slows the rise in blood glucose following a meal varies from person to person. If you find that certain meals affect your postmeal blood glucose levels in a predictable fashion, you may be able to fine-tune the timing of your premeal injections or boluses accordingly.

Practical tips
Meticulously timing your rapid-acting insulin dose and carefully calculating your dose according to the carbohydrate you will eat is usually best for blood glucose control, but it may not always be possible. There are times when you know exactly when and how much you will eat and times when you don’t. For example, if you are trying out a new restaurant, eating at a friend’s home, or not feeling well, you may not know exactly when or what you will be eating, which can make it difficult to know how much insulin you’ll need and when to take it. In addition, if your blood glucose level is low before a meal, you may have to give the food, not the insulin, a head start. The following practical tips may help you adjust for the realities of daily life:

High blood glucose before a meal. If your blood glucose is high before a meal, use your insulin sensitivity factor (how much your blood glucose level falls in response to one unit of insulin) to calculate a dose of rapid-acting insulin to cover the high, then wait until that insulin begins to lower your blood glucose before you eat. This method is easier and more convenient for insulin pump users. (For people who are willing to take an extra injection but who don’t want the hassle of carrying a vial of insulin and syringes, an insulin pen may also add some convenience.)

Claudia Shwide-Slavin, a dietitian and certified diabetes educator in private practice in New York City, advises the following: "If your blood glucose level is between 140 mg/dl and 180 mg/dl, take the rapid-acting insulin and wait half an hour before eating. If it’s between 180 mg/dl and 200 mg/dl, wait 45 minutes. If it’s higher than 200 mg/dl, wait at least an hour." She also notes, however, "I have seen it take two hours after an injection for blood glucose levels to budge." If a person is hungry or must eat at a specific time, Shwide-Slavin recommends limiting the amount of carbohydrate at the meal by eating mainly protein and nonstarchy vegetables.

Another suggestion from Shwide-Slavin if you can’t delay a meal is to "check your blood glucose an hour before you think you will eat. If it is high, take a correction dose so that your blood glucose will be on the downswing by the time you eat."

Low blood glucose before a meal. If your blood glucose is low before a meal (below about 80 mg/dl), "Wait to take your insulin," says Shwide-Slavin. "Let the food have 15 minutes to raise your blood glucose before taking your insulin."

Low glycemic index foods. On a related note, Wolpert advises, "If your blood glucose is less than 100 mg/dl before a meal and you plan to have a meal with a low glycemic index, wait until you start to eat to take your rapid-acting insulin."

Uncertain carbohydrate intake. If you don’t know how much carbohydrate you will eat at a meal, consider splitting your rapid-acting insulin dose. Take enough insulin before the meal to cover the amount of carbohydrate you are sure you will eat. Then as the meal goes on and you know how much more carbohydrate you will eat, take more insulin to cover that amount. This method is easiest if you are on an insulin pump.

Large meals. Splitting your rapid-acting insulin dose can also work well for meals that are larger than normal. It has been shown that large meals can delay the rise of blood glucose regardless of the nutrient composition of the meal.

Also in this article:
Insulin Resources

Hope Warshaw is a dietitian and diabetes educator in Northern Virginia. She is the author of numerous books about diabetes nutrition management including Complete Guide to Carb Counting, 2nd ed. (2004) and Guide to Healthy Restaurant Eating, 3rd ed. (March 2005). Both books are published by the American Diabetes Association.

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