Snacks and aerobic activity
Under certain conditions, eating extra food is necessary to prevent hypoglycemia during exercise. For example, if you are going to exercise before or between meals, reducing your premeal insulin at the last meal you eat before exercising would only serve to drive your pre-workout blood glucose level very high. A better approach would be to take your normal insulin dose at the meal, then have a snack before exercising. If you engage in unexpected exercise soon after you take your usual insulin or other medicine, snacking will be your only option for preventing hypoglycemia. Also, during long-duration endurance activities, hourly snacks, in addition to reducing insulin or other medicines, may be necessary for preventing hypoglycemia.
The size of the snack you choose depends on the duration and intensity of your workout. The harder and longer your muscles are working, the more carbohydrate you will need to eat to maintain your blood glucose level in target range. The size of your snack also depends on your body size: The bigger you are, the more fuel you burn while exercising, and the more carbohydrate you need.
There is no way of knowing exactly how much you will need, but the chart “Carbohydrate Needed per Hour of Activity,” should show you some safe starting points. To use the chart, find your approximate body weight and look down the list to find the intensity of your exercise. The number in the column represents the grams of carbohydrate that you will need per hour of activity. If you will be exercising for half an hour, consume half the amount before your activity. If you will be exercising for two hours, consume the full amount at the beginning of each hour.
The best way to determine the optimal size and frequency of your snacks is to check your blood glucose before and after the activity. If it holds steady, you have found the magical amount of carbohydrate for your activity. If it rises, cut back on the amount of carbohydrate. If it drops, add some more grams of carbohydrate or eat more frequently the next time.
As mentioned previously, it is not unusual to experience a rise in blood glucose at the onset of high-intensity, short-duration exercise. This is caused by a surge of stress hormones that accompanies such activities. Exercises that often produce a short-term blood glucose rise include the following:
- Weight lifting (particularly when using maximal weights or lifting to the point of failure/exhaustion)
- Sports that involve intermittent bursts of activity, like baseball or golf
- Sprints in events such as running, swimming, and rowing
- Events where performance is being judged, such as gymnastics or figure skating
- Sports activities in which winning is the primary objective
Liz, mentioned earlier, was experiencing this exact problem. During swim practices, her blood glucose would drop steadily, requiring extra snacks. But swim meets caused just the opposite effect. Her blood glucose would rise sharply during swim meets due to the stress and competitive nature of the events, and this would hinder her performance. Once she eliminated snacks before meets and instead started taking a little extra insulin beforehand, her blood glucose levels stayed closer to normal and her performance went to a whole new level. In her first meet trying this approach, she set a personal record and took second place in the 50-meter freestyle!
Covering the highs
To determine how much extra rapid-acting insulin to take before a competitive event or any other activity that tends to raise blood glucose, consider how much your blood glucose normally rises during the activity. If it goes up 200 mg/dl and your sensitivity factor is 50 mg/dl per unit (meaning that your blood glucose level drops 50 “points” per unit of insulin), you would normally need to take 4 units to prevent the rise. However, if you take your normal 4 units before exercise, you might pass out. (Remember that physical activity makes your insulin more potent.) Instead, take half the amount you would normally take. Give it about half an hour before your activity so that it will keep your blood glucose level from being too high when the activity begins.