Questions and Answers - exercise

Q: Why does my blood sugar increase after exercise? I had a blood sugar reading of 135 first thing in the morning. After a 3 mile walk my reading was 155.
A: Wait an hour after you exercise and see if you get the same results. Exercise is a stressor, so blood sugar will be higher immediately after your session. Also, blood sugars tend to be higher in the mornings because of hormonal activity during the night.

Q:  My husband has had type 2 diabetes for 15 years. He has gotten his food and exercise in pretty good shape and has his A1C down to 6.5. My concern is that he will do strenuous exercise in the morning, often for 2 hours, before he eats a meal. Is it safe to exercise this long while fasting?  
A:  Much depends on what his pre and post-exercise levels are as well as his overall health and energy. If he experiences lows 30-60 minutes post-exercise, then he needs to fuel up before exercising. Some version of a meal shake - containing a balance of carbs, protein and fat - works well for many people. If he has no issues, then his body appears to have adapted to the consistent program he has developed that appears to be working for him.

Q: I have type 2 diabetes and have been walking 4-5 miles every night for the past six months. How come I'm not losing any weight?
A: Lean tissue weighs more than fat so you often won’t see the number on the scale change, but will feel better, have more energy, better glucose levels, etc. In time, the weight number starts to come down. Keep up the exercise. Get assistance with your eating if you are at all unclear about how to manage food intake with diabetes.

Q: I've had type 1 Diabetes for 26 years and am 15 pounds over my ideal weight. For the last 6 weeks I've been attending a fitness boot camp. I find that my sugar levels may start at around 100 but steadily rise for the hour after exercising. Is this normal? 
A:  Exercise is a "stressor", meaning that in the short term, exercising will raise glucose levels before they drop down. Without diabetes, levels only rise up to a threshold point. With type 1, especially, levels may rise and take several hours to come back down. This is another reason why it is more challenging to find the right insulin dosages for the various differences in the day's activities and eating. Of course, exercise is always encouraged, as lean tissue burns up more calories, requiring more fuel. This fuel is accessible from glucose in the bloodstream. In the long run, your levels should eventually be lower. If you should drop too low a few hours after exercising, reassess your coverage for exercise. Losing your extra body fat should eventually help you in get better post exercise numbers.

Q: What is the best after dinner exercise for someone with pre-diabetes?
A: There is no one perfect exercise, but at that hour and having just eaten, a good walk is usually the best for most people.  Any activity that is too long and/or strenuous later at night may cause one to stay awake.  For some folks, especially those on insulin, strenuous evening exercise may cause early morning low blood sugars.  Try those after dinner exercises you enjoy and see how they affect you. Ultimately, you are shooting for lower fasting glucose levels.

Q: I usually run 10 to 14 miles on the weekends but I was recently diagnosed with type 2 diabetes. First, why does exercise seem to raise my blood sugar? What do you suggest eating before, during and after the run to give me the energy needed to complete this? I've always carried the little energy gel packs but I'm not sure this is the wise choice with diabetes.
A: To address your first question, a run of that intensity will certainly first elevate your blood sugar before it lowers. It is suggested to generally wait at least 1 our post-exercise before testing.

            Your pre-run snack accomplishes 2 things: get quick energy fuel while having some in reserves. The first rule is to eat whole, "real" foods such as pure ground peanut butter. A breakfast shake does very well for many people. You want minimal digestion with maximum absorption. What constitutes the best pre-run meal can vary among individuals, and much depends on how you eat the rest of the time. This means creating a fine balance among carbs, protein and fat so that you have a good access to both immediate and long term fuel. My personal morning preference before a workout is in a shake form. Some people can manage a yogurt based smoothie. Peanut butter stirred into oatmeal (if that appeals to you) is a better carbohydrate source than a bagel because of its fiber types. There are also many meal replacement powders out there: some good; others not so good. Berries and banana are good fruit choices to consider adding in a small amount.

            Long runs do require fuel and hydration without upsetting salt balance. Of course, your weather conditions must be factored in. As a general rule, for each hour of exercise, 30-50 grams of carbs are recommended so a gel pack may be appropriate during the run only.  After a long run you want immediate carbohydrate replacement like a low-fat yogurt, and then having a meal awhile later. In general, eating legumes, lean "flesh" foods, and veggies on a daily basis can provide the best foundation for overall performance.

            No two people with diabetes are alike. You are going to have to "self-experiment" over time to see what works. Diabetes doesn't mean "stop"; it does mean "pay closer attention" and continue to enjoy life.

Q: I have type 1 diabetes, have good health, and enjoy taking high intensity aerobic classes like Zumba. The problem is that my blood sugar often drops to 45-60 during the class no matter how much I carb up prior. I try to start with a BG of 150-170 and check half way through then treat with glucose tabs or juice and keep going. After class, my BG may range from 60-100 but then rises up to 200+ for the next few hours and I have to treat with insulin. What can I do? 
A: You are definitely experiencing the exercise effect, which will raise your blood sugar for up to 4 hours after exercising. Have you started by cutting your post-exercise treatment dose in half? Also, if you are eating within that 3 hour time frame, stick to a lower carbohydrate protein/veggie type meal rather than any starchy carbs. Also, are you changing your basal rate for exercise? I know some very active folks program as many as 8 rates/day. Sounds like you should lower yours for class if you are not already doing so.

Q: I have had type 1 diabetes for 23 years. There was a time when my blood sugars would plummet after a workout. However, now when I exercise, my blood sugars are sky rocketing and I'm not eating anything. My blood sugars are perfect before I workout. What is up with this? 
A: If the intensity of your workout has increased and you are testing within the 1/2-1 hr. post-exercise, it may be you need to wait longer for the post test. Exercise will generally increase levels in the short run, then drop in the long run. This is even more pronounced with insulin dependence. You may need to adjust your carb/insulin ratio before you workout. If all else is the same in your life except for the workout intensity, then rechecking even up to 4 hours later may be a path to try, in the short run, to see what the drops may be, then discuss any needed adjustments to your protocol with your physician if necessary.

Q: I'm a type 1 diabetic and I am trying to incorporate exercise in the morning. However, it seems that my blood sugar spikes when I do this. This morning my blood sugar was 182 when I woke up. I did a 20 min work out video and took a shower. About a half hour later I tested my blood sugar and it was 300. Is there anything I can do to avoid this? I should mention I take lantus before bed and humalog with meals. When I exercise at other times of the day my blood sugar usually goes low.

A:  Blood sugar levels are generally higher in the morning anyway due to the rise of hormones - this is known as the Dawn Phenomena. In the short run, exercise is a stressor and will elevate levels. In most folks, 30-60 minutes after exercise, levels will lower. Often in type 1 diabetes, however, it takes longer for levels to come down post exercise. You should discuss this with your physician to see about a target for the fasting levels pre exercise and how that is to be accomplished with your current protocol. As we know, this is easier said than done.

Q: When is the best time of day to exercise? I don't want to exercise and have my blood sugar drop.
A: The best time to exercise is any time that you can fit it in as opposed to skipping it!  It is also important to have enough fuel in your system to cover your activity. There are general guidelines:  for a 30 minute brisk walk, it is recommended to have 15 grams of carbs if your blood sugar is under 120.  This would mean a small fruit or a yogurt can work well as it has carb and protein.  As your exercise time increases, so may your intake needs. The best way to determine your needs and best exercise zone is to test before and after exercising.  If you are comfortable soon after your meal, that is a great time as you are well fueled. 

Q: I plan to do a one-week, 75 mile backpacking trip this summer. As you may know, backpackers often burn 4000 to 6000 calories per day, due to the strenuous nature of the exercise. Presumably, during exercise like this, my body will require much larger than normal amounts of carbs. Is there any guidance you can offer regarding the appropriate increase? What kind of percentage split between carbs, protein and fat would you recommend? 
A:  Good for you! Now, no one shoe fits all; gender, height, weight, body fat %, etc. all determine one's needs. Checking your glucose levels will let you know how your food is working for you. Legumes and whole grains like quinoa and wild rice can be part of a good carb loading program. If you are eating unrefined foods on this trip as opposed to quick acting carbs like candy/energy bars, you may find your energy more stable for longer periods. Nut butters work well on such trips. Bananas are a good sustaining fruit. Eggs are a good protein source for those who eat them, especially for the morning start. Since the general guideline is for 45-65% of intake to be from carbs, a 4000 calorie intake would be 450 grams form carbs at 45%. Remember: veggies are carbs. These are your immediate muscle fuel sources. Pack smart, and check as often as you think you need to, and avoid low blood sugar.

Q: I have been diabetic for 43 years and on the pump for 17 years. I am a bicyclist and train hard for races. I ride five days a week. I do not suspend or lower my basal during training. This year I have scaled back slightly and do two recovery rides a week. I have found that the recovery rides make my blood sugar skyrocket to as high as 411. I have tried eating different things prior to training but nothing makes a difference. What suggestions do you have to keep my BG from raising so quickly and so high? 
A: With the regimen you have described, I would think you have different basal rates programmed into your pump, being different on the recovery days, reflecting a higher rate. What you eat is, of course, a factor, but your insulin:carb ratio may also need to be increased on those days. Be sure you are not eating refined carbs on your recovery days, aiming for higher fiber sources. Your pump company can also be a good resource if you already haven't tapped them for assistance with this issue.

Q: My girlfriend has type I diabetes and is considering training for a full marathon 10 months from now. She is currently about 40 lbs over weight and is not running. I know she needs special advice from her doctor and possibly a nutritionist, but I don't want to set her up for a goal she cannot accomplish.
A: Jumping right in to run would not be a good thing. The first thing to consider is if her blood sugar levels are in close-to-normal ranges. Hopefully, her physician has given her ranges to target. Exercise for Type 1's needs to be closely monitored, especially when doing longer sessions such as running a marathon. She will also need to be aware that hypoglycemia may actually occur during sleeping hours depending on the duration of the activity and food intake. Good hydration is also a "must". I would suggest that if she is serious, she needs to gets some guidelines from her physician. Daily, she should do a minimum of 45 minutes fast walking, gradually increasing, including stretching before and after. If she is cleared as healthy for a marathon by her physician, she needs to be prepared to monitor her glucose carefully before, during, and after exercise. Be sure she has proper footwear, and checks her feet daily.

Q: When I exercise my upper body, my blood sugar goes up and when I exercise the lower part, my blood sugar goes down, why is this? 
A: How soon after exercising are you checking your blood sugars? For those not on insulin, I always suggest at least an hour, since exercise will raise your blood sugars initially, then "settle" down. If you are more dependent on insulin, blood sugars may be high several hours later. Lower body exercises generally burn more fuel (sugar) due to increased muscle mass. It may just be that on those days your blood sugars are coming down more quickly. Try consistent timing of testing, and see if you don't notice a change.


Information on the "Question and Answer" pages should not be relied on for medical or technical advice. Always consult your healthcare team. Diabetes Action and Jane DeVane cannot be responsible for errors or wrongful use of the information available on this website. The information provided on this site is designed to support, not replace, the relationship that exists between a patient/site visitor and his/her physician/medical team.