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Physical Activity Is Only One Part of the Equation

By Sheri Colberg, Ph.D.

As an exercise physiologist, I first and foremost focus on the physical activity part for management of blood glucose levels, often stating that being active will increase insulin action, lower blood glucose levels, and make diabetes management easier. In reality, not all of those benefits are fully evident in many cases. In fact, they usually cannot be counted on unless you take into account myriad other factors that can have an equally—if not more—dramatic effect on blood glucose management.

Although a single bout of exercise usually improves insulin action for 2 to 72 hours afterward, the effect also depends on how much you eat before, during, and after working out, how you manage your diabetes medications (particularly insulin), your prior control over your blood glucose levels, how much sleep you get, whether you’re stressed out or not, etc. As you can imagine, it’s not easy to manage and predict all of the possible effects of these various things.

Writing this article on the inauguration day of the new U.S. president (January 20, 2017), I was vividly reminded how much of an impact that stress (mental or physical) can have on blood glucose management. Sometimes it feels like stress can override any or all benefits you were supposed to receive from being active. Getting upset, angry, anxious, frustrated, sad, or depressed can basically erase your improvements in insulin action, although on the flip side, working out can also lower many of those negative feelings if you exercise after they occur. Not only is exercise an acute mood enhancer, but it also allows you to get tired enough that you don’t have as much energy to devote to sustaining your negative emotions.

Having a nasty cold last week also reminded me that simply being sick—even moderately so—can really wreak havoc on blood glucose levels. For me, exercising doing anything other than moderate walking is hard when I’m sick, and you really shouldn’t exercise much or intensely when you’re sick anyway or you can make your illness worse. Exercise acutely lowers the concentration of illness-fighting immune cells in the bloodstream, and simply overtraining can increase your risk of getting colds and the flu. If you normally use exercise to manage your blood glucose levels more effectively and you’re deprived of doing that while sick, you can often find yourself dealing with not just one thing (illness) that can raise your blood glucose, but two at the same time (lack of exercise being the second). On top of that, you may not be sleeping as well as normal because of being sick, and lack of sleep raises insulin resistance as well. Nothing like a simple cold to throw your whole diabetes regimen out of whack!

It’s also so incredibly easy to override the effects of your last workout with food. You may not want to focus on how much/long you have to exercise to expend enough calories to equal what you eat on a daily basis (it’s a whole lot!), but suffice it to say that most people overestimate the impact of their exercise and underestimate the calorie content of the foods. Most people have to walk at least a mile to burn off close to 100 calories. A modest handful of nuts has closer to 200 calories, and get a burger at a fast-food restaurant and you’ll probably take in over 1,000 calories. Just keep in mind that food can easily have an even greater impact on your blood glucose levels unless you’re one of those avid exercisers that exceeds the daily recommended amounts (30 minutes of moderate activity) by exercising hours a day.

If you already exercise regularly, sometimes you fail to get the same glucose lowering effect as someone who is just starting out with training. With training, your body becomes adapted to the activity, which can make fat use higher and blood glucose use lower during the same activity. So, what used to really feel like it revved up your insulin action afterwards may not do much for you anymore, and when you don’t do your usual activities, you pay the price of having to deal with rising blood glucose levels unless you up your medications or cut back your food (or both).

It may sound like I’m trying to talk you out of exercising regularly to help with diabetes management, but really nothing could be farther from the truth. I’m simply warning you that life can throw many different monkey wrenches into your usual responses, so go easy on yourself when you don’t get it right every time. Lose the guilt, and just manage your blood glucose levels the best you can on any given day and stay active for your overall health.

In addition to my educational web site, Diabetes Motion (, I also recently founded an academy for fitness and other professionals seeking continuing education enabling them to effectively work with people with diabetes and exercise: Diabetes Motion Academy, accessible at Please visit those sites and my personal one ( for more useful information about being active with diabetes.