f you are a diabetic, there may be times that it’s better not to exercise, at least until you get your blood sugars down.
It’s a popular half-truth that exercise always lowers blood glucose levels. The reality is that exercise really does lower blood sugars through an increase in the number and activity of glucose transporters in muscle provided:
· There’s adequate insulin in the bloodstream.
· The period of exercise has to be long enough.
· Blood sugars can’t be too high before exercise, and
· For most diabetics, the exercise is not done within three hours of waking in the morning.
Any exercise that makes you even a little short of breath will release a surge of stress hormones such as cortisol. These stress hormones stimulate the liver to convert glycogen into glucose to make sure the muscles have enough sugar to burn.
If there isn’t enough insulin in circulation, however, glucose can’t be transported into the muscle cells that need it. It’s not unusual for swimming, climbing, weight lifting, or basketball to cause surges to the 300-400 mg/dl (16.5-21 mmmol/L) level in diabetics. If there is not enough injected insulin, or the body’s own insulin is insufficient, exercise, paradoxically, results in higher blood sugar levels, not lower.
Also due to the effects of cortisol and epinephrine, brief strenuous exercise raises blood sugar levels, while prolonged strenuous exercise lowers them. If you exercise for just a minute of two, say, doing one set of six repetitions in your weight lifting routine, the resulting release of cortisol will trigger the liver’s conversion of glycogen to glucose.
The first 1-2 minutes of heavy exercise release the glucose muscles need, but you need another 6-8 minutes for muscles to use the glucose and get blood sugars back down. Prolonged heavy exercise, that is, at least 20 minutes, will increase the rate at which muscles use glucose for their recovery for 1 to 3 hours.
You might consider just lying on the couch if your sugars are over 170 mg/dl (8.5 mmol/L). That’s because the sugar released during exercise has another effect on muscles, creating insulin resistance.
Glucose in the bloodstream can oxidize even before it is absorbed by a cell. This “burning in the bloodstream” releases toxic free radicals that can damage muscle cells.
The cells protect themselves by becoming less responsive to insulin so they do not import either the glucose or the free radicals. Over time, however, they become less and less responsive to insulin even at rest. That’s why exercise to lower unusually high blood sugars generally is not a good idea, unless it is extremely gentle (like walking slowly).
Finally, most diabetics should not be morning exercisers, especially if fasting sugars test as high as sugars throughout the day. The body recycles insulin during sleep, so less insulin is available early in the day. When there isn’t enough insulin, exercise cannot lower sugars.
None of this means that diabetics shouldn’t exercise. Quite the opposite, regular, prolonged, heavy exercise builds up muscles which in turn soak up glucose. To make healthy muscles, however, always start your workout knowing your blood sugars are under control and take steps to ensure they will stay in control throughout.