It’s one of the many ironies of insulin-dependent diabetes: Exercise helps manage it by helping our cells become more efficient, but exercise also can cause our blood sugar levels to plunge. What’s with that?
To understand this, we must first look at what happens when we make the radical decision to foist ourselves off the couch, violating Newton’s first law of motion, which states that a body at rest will remain at rest.
To propel that body into motion takes a tremendous amount of energy, which will first come from stored carbohydrates, and then from our body’s stored fats. If we keep going, as our energy reserves are depleted, our glucose levels diminish as the exercising body dips repeatedly into its energy well. This is true even for people who don’t have diabetes. But for those of us who do, the threat of hypoglycemia (generally defined as blood glucose levels dropping to around 4.0 mmol/L or 80 mg/dL) is something we must take seriously and counter-attack, with vigilant monitoring and planning of pre- and post-exercise snacks.
It’s important to note that the effect of exercise on glucose levels depends on what kind of exercise we’re doing. Blood sugar diminishes during moderate-exertion, sustained activities such as running or swimming for an hour or more. Our glucose levels can actually increase during short bursts of strenuous activity, such as weightlifting, tennis, or kickboxing – which is especially problematic for me.
The risk of hypoglycemia, however real, is no excuse for any of us to lead a sedentary life. I’m a triathlete who was diagnosed T1 at age 3, and despite the challenges of diabetes, I can out-run, out-cycle and out-swim most people who’ve never had an insulin deficiency in their lives. In fact, having diabetes probably makes me a better athlete, since I’ve learned to pay close attention to my body and its subcutaneous needs.
As an athlete with diabetes, I’ve learned, through trial and error, how my body responds to exercise, whether it be 30 minutes or four hours. I know what to eat in advance of an event, what to eat during an event, and what to eat (and do) immediately after, and hours after I’ve stopped. (Ironically enough, some people with T1 may need to exercise AGAIN after exercising. For example, if your glucose is low after a long, slow run, you might want to sprint for a few minutes to send it rising again.) Though, even after a few decades of living with diabetes, I’m still learning and don’t always get it right.
As the late runner-philosopher Dr. George Sheehan once said, we’re all an “experiment of one.” What works for me in my training might not work exactly the same for you. Learn from the experience of others, and consult your doctor when first beginning an exercise program.
But your body should be your most-trusted adviser. Pay close attention; it will usually tell you what you need to know.