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Answer: Measure your blood glucose (BG) before each exercise session. If it is within normal limits or only slightly higher, say 120 mg/dl or so, then you may well need some food before exercising. However, if the value exceeds about 180, then you may not need to eat additional food.
A strategy many regular exercisers use is to exercise about 45 to 60 minutes after a meal. BG at this time typically will be in the 150 to 200 range, so an ample supply of glucose is available to the muscle. If the exercise session lasts 30 minutes or less, then insulin reaction would be unlikely to occur. However, if a longer and more strenuous session occurs, then the glucose lowering effect of activity continues for a longer period and the BG may reach a hypoglycemic level. By recording BG before and after exercise each session, you will see a pattern emerge. If your BG is too low in the last portion of exercise or soon after exercise and the activity was performed after a meal, you need to adjust your medication or food intake. You could either reduce the amount of oral medication or insulin that is active at the time of exercise, or you could eat a bit more food. The former is preferable if you are trying to lose weight while the latter would be acceptable for someone who is lean.
Eliminating insulin reaction during exercise is easier than preventing it hours after exercise. After exercise, the muscle and liver glycogen levels are lowered and the metabolic activity of the muscle is increased for several hours. Consequently, glucose enters the muscle and liver at a greater than normal rate. These factors may cause insulin reaction hours after the exercise. Therefore, it becomes necessary to do some additional BG monitoring later in the day. If the exercise was unusually long or vigorous, such as spending a day hiking, working in the yard, etc., then BG should be measured during the day several extra times, before going to sleep, and even in the middle of the night and next day.
While this may seem like a lot of extra BG testing to do, I look on it as a virtue. People with diabetes can be extremely active. Before BG monitoring could be done at home, active people with diabetes pretty much had to adjust their medication and food by feel. Monitoring allows us to be far more precise and prevent reactions during and after physical activity. It is my observation that physically active diabetics tend to do quite a bit more monitoring than others. This is consistent with the recently published results of the DCCT study in which additional monitoring was associated with better BG control and reduced retinopathy, neuropathy, and nephropathy.
In summary, use BG monitoring to study how a given amount and type of exercise affects you. Make adjustments based on the data. Insulin reactions should not frequently occur as a result of exercise. If they do, consult your physician or diabetes educator.
Kris Berg is an Exercise Physiologist and Professor of Exercise Physiology at the University of Nebraska at Omaha, as well as the author of the book "Diabetic's Guide to Health and Fitness." He runs daily, lifts weights regularly, and has had type I diabetes for 37 years.
If you have exercise related questions, send them to Kris Berg, c/o DIABETES HEALTH, 3715 Balboa St., San Francisco, CA 94121.
Diabetes Health is the essential resource for people living with diabetes- both newly diagnosed and experienced as well as the professionals who care for them. We provide balanced expert news and information on living healthfully with diabetes. Each issue includes cutting-edge editorial coverage of new products, research, treatment options, and meaningful lifestyle issues.