Detecting the spikes
A number of good options exist for measuring after-meal blood glucose spikes. Perhaps the most practical is to check your blood glucose level about one hour after completing a meal or snack using a blood glucose meter. When checking your blood glucose level after meals or snacks, you should use a blood sample from a finger rather than an alternate site sample. Because of the way blood circulates in the body, samples from the fingers may show changes in blood glucose level sooner than samples from other sites. Check before and after breakfast, lunch, and dinner several times to determine whether postprandial spikes are a problem at a specific meal. It is more common to see significant spikes after breakfast than at other meals, but it is worth checking after each meal just to make sure.
When interpreting your results, take your premeal readings into account since you are interested in not just your after-meal reading but also in how much your blood glucose level increased because of your food intake. For example, a postmeal blood glucose reading of 240 mg/dl following a premeal reading of 210 mg/dl shows just a 30-point rise, whereas a 240 mg/dl following a 110 mg/dl shows a 130-point rise. Having a mildly low blood glucose value (around 65 mg/dl, for example) before a meal can result in a temporary “rebound” to a higher-than-usual level after the meal and may not reflect a true postprandial spike.
Another option for analyzing after-meal blood glucose levels is the GlucoWatch Biographer from Cygnus Corporation. The GlucoWatch takes readings every 10 minutes by measuring the concentration of glucose in the interstitial fluid just below the skin. The data can be reviewed manually or transferred to a computer for analysis. However, one of the problems with using the GlucoWatch is its tendency to “skip” readings during periods of rapid blood glucose rise or fall, as usually occurs soon after eating.
A more detailed analysis of after-meal blood glucose can be obtained through use of the Continuous Glucose Monitoring System (CGMS) from Medtronic MiniMed. The CGMS can be worn for up to three days and measures glucose levels in interstitial fluid by way of a tiny sensor inserted just below the skin. It does not provide immediate data. Instead, the information is transferred to a computer after the sensor is disconnected from the skin. The software provides statistics and graphic printouts that allow you and your health-care team to see exactly how much your blood glucose levels are rising after meals and snacks. (See sample printouts in “How Bolus Timing Affects After-Meal Spikes”).
Reducing after-meal spikes does not always mean taking more insulin or oral medicine at mealtimes. In fact, if your premeal readings are already close to normal, increasing your dose of insulin or oral medicine would result in low blood glucose before the next meal. Remember, the idea is to reduce the between-meal peak, but not necessarily lower the blood glucose level before the next meal.
To accomplish this feat, a number of strategies can be used, including the following:
Get moving. Physical activity after eating has a multitude of benefits. If insulin was taken with the meal or snack, the enhanced blood flow to the skin surface caused by physical activity is likely to make the insulin get absorbed quicker so that it can act quicker. This means that the insulin will do a better job of keeping the blood glucose from rising too high right after eating. In addition, muscle activity diverts blood flow away from the intestines, resulting in slower absorption of glucose and other simple sugars into the bloodstream. The sugars that do enter the bloodstream are likely to be “consumed” by the working muscles.