Have you ever wondered why your blood sugar falls during certain types of exercise whilst increasing during and types of exercise? Or why you sometimes get high blood sugars after exercise?
If you’re curious about the scientific explanation of how exercise can raise blood sugar, read on.
I rarely come across scientific studies that explore how exercise affects blood sugar in people living with type 1 diabetes, so when I recently got my hands on just such a research paper, I dug in with great interest (they specified type 1 diabetes, but I would think that the results are applicable to anybody using insulin).
Well actually, Google and I dug in. This research paper is heavy reading. You know those scientific papers where you feel like you need an advanced degree (plus a whole lot of Googling) just to understand the introduction? This is one of them.
The paper is titled “Effect of intermittent high-intensity compared with continuous moderate exercise on glucose production and utilization in individuals with type 1 diabetes”, and is written by a team of scientists from Australia. It was published in the American Journal of Physiology – Endocrinology and Metabolism in 2007 (not exactly new research, but peer-reviewed research nonetheless, which means it’s legit).
I thought that the subject was relevant and interesting enough to spend the time reading and understanding it. So, since I’ve done the heavy reading, let me share what I’ve learned with you.
Exercise and blood sugar impact
So why do some types of exercise make our blood sugar drop like crazy while others make it increase or hardly have any impact? I know from my own experience that I really have to watch my blood sugars if I do steady state cardio, while an interval training session will have little impact or even make my blood sugars go up.
It turns out that the main reason why interval training won’t make your sugars drop as much as steady state cardio comes down to two factors.
- Increase in glucose production
- Glucose utilization
Both of these factors are affected by exercise, regardless of the type of exercise you do. However, the scientists found that after 15 minutes, there was a statistically significant difference in the two factors depending on whether the test subjects did interval training or steady state cardio.
They found an overall higher production of glucose, both during and up to 2 hours post-exercise in the test subjects that did interval training when compared to those doing steady state cardio. Glucose utilization was also higher for the interval training group, but it never caught up with the glucose production.
This means that interval training has less of an impact on blood sugars (despite the interval training group putting in more overall work) than steady state cardiovascular training because your body is producing glucose as fast or faster than you can use it.
The scientists don’t know exactly why we see the greater increase in glucose production for interval training, but they theorized that it might be due to muscle glucagon breakdown.
Another finding was that cortisol (the stress hormone) didn’t increase more with interval training. That’s a really positive finding since increased cortisol isn’t something we generally strive for due to the many negative side effects such as weight gain, impaired immune function, and gastrointestinal problems.
How to implement the research findings
Aside from me finding this super fascinating, what can we do with this information?
I think that this is a great piece of knowledge to have for trained athletes, those who are just starting out, and for parents managing their kid’s diabetes. It can serve as a guide when determining the amount of insulin and carbohydrates to safely administer prior to and post an activity.
The scientists compared interval training to sports like basketball and soccer where you have intense bursts of activity. I would add newer sports such as CrossFit, HIIT (high-intensity interval training) and HIT (high-intensity training). It could also be boot camps, spinning classes, or if you just do a lot of cardiovascular interval training and heavy resistance training.
Armed with this scientific knowledge (and a lot of experience), I know that I don’t need to reduce my insulin as much before and after an interval training or a resistance training session (I may even need a little extra insulin(!)), while I will need to make reductions if I do 40-60 minutes of steady state cardio.
For me, steady state cardio can be a long walk, a bike ride, or walking on an incline, Stairmaster or elliptical. With all of these activities, I’ll see an almost instant drop in blood sugars. However, the improved glucose utilization wears off pretty quickly after I stop exercising, so I know to lower my insulin prior to steady state cardio but not after.
To summarize:
- Exercise impacts BOTH glucose production and utilization
- When doing interval training, increased glucose production outpaces your increased glucose utilization
- When doing steady state cardio, glucose utilization dominates production
- Because of this, your blood sugar may rise during and after high-intensity interval exercise, while it most likely will drop during steady state cardio
I hope this post answered the question “does exercise increase blood sugar?” If you want to learn more about managing your blood sugar during exercise, please read my article “How to Manage Your Blood Sugars When Exercising with Diabetes“.
You can read the full scientific paper here: Guelfi KJ, Ratnam N, Smythe GA, Jones TW, Fournier PA.:“Effect of intermittent high-intensity compared with continuous moderate exercise on glucose production and utilization in individuals with type 1 diabetes”: Am J Physiol Endocrinol Metab. 2007 Mar;292(3):E865-70.
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Mehdi
Hi Christel,
Thank you so much for your article !
I have the Freestyle Librelink and recently noticed that I have the dawn phenomenon. My blood sugar keeps increasing from 4 am to 8 am… I didn’t have that in the past.
I usually wake up at 6 am and go to the gym. I do biking for 15/20mins and HIIT workouts. My blood sugar level keeps increasing after biking…
I eat generally after working out and don’t eat anything before training.
– Do you have nutriments you would recommend to stop the dawn effect ? I’m not ready to take another shot of insulin. I have read vinegar / alkaline diet
– What should I do after my training ? Do you think I should eat and get my insulin intake before training ? Can I keep the same level of insulin ? my objective is to reverse my diabete. I succeeded at decreasing my insulin level by half and don’t want to increase it again.
Christel Oerum
Sounds like you live with type 2 diabetes, given that you could try exercising before bed and consuming most of your carbs earlier in the day to try and limit the impact of your Dawn phenomenon. As for those increases during after training, you’re thinking is much in line with what I usually recommend. Try having your meal and meds before your workout, that can help reduce the amount of glucose your liver dumps into your system, and another bonus is that you might have more energy for your workouts.
bruce
Hi, I ran ultra marathons…and notice when i do intense exercise, do a long run, my blood sugar spikes from 103 to 124. But settles down after three days or two. When i do yoga with a few laps of swimming my bs is from 98 to just a few hundreds. Your comment on this please. Thank you very much.
Christel Oerum
Hi Bruce, I need a little more context to give you a great answer. But this could be a start.
For people living with diabetes intense exercise (races, HIIT, etc.) tends to elevate BGs however, it will usually come down in the hours after. When you say it takes a few days, does that mean you don’t take any meds? If not, I’d suggest you talk to your doctor, elevated BGs for that long might have to be medicated. In general, if you tend to have high BGs for longer durations of time after exercise something might be off. Maybe you’re hurting yourself = inflammation or infections or something else is going on. Regardless I think getting blood work done and having a good chat with your medical team is a good first step
Marek
Are you diabetic? Because for a type I those swings are negligible at best and really not something to be concerned about. It sounds like you may be pre-diabetic or even type II with minimal natural insulin resistance but I’m really surprised you have such exact numbers which you can replicate. I’d suggest bringing this all up with your doctor as they may want to get you on some type of BG control medication to keep it under the ~100 mark like usual non-diabetics have naturally.
Carmelo Banados
Very interesting article. I wear a Freestyle Libre CGM and I just finished my first spin class which turned out to be 60 minutes of intense effort. I definitely saw a spike in my BG during and after the workout. It’s been 30 minutes after the session and only now is my BG starting to decline back to normal. I hope that long term…high intensity workout like this will reduce my insulin resistance.
Christel Oerum
That type of exercise should increase your insulin sensitivity after your workout and in the long run. Increased insulin sensitivity will mean that you most likely will have to adjust your insulin to not go low. Keep rocking
Janae
Hi Crystal,
I’ve been following your blog and book for a while now and have learned so much. Unfortunately, I am still having trouble controlling my sugars and my last A1C was 9. I’m a type 1 for 18 years and just when I think I have a handle on it it changes. I am pretty active and do a lot of interval training. I’m not sure where you are located but I was wondering if you take on personal clients?
Christel Oerum
Hi Janae,
I’m so glad you find the website and book helpful. And I’d be happy to support you. I work with people in person in Los Angeles and online all over the world, so I’m sure we can figure something out. Shoot me an email at contact@diabetesstrong.com and we can chat.
And please hang in there, it’s not easy, but it’s so worth it.
Christel
Michael
Yea! I notice that my blood sugar level tends to increases while I do interval training or weight training. My blood sugar level tends to decrease while I ride my bicycle or walk or power yoga. I think people with type 1 diabetes are different individually. T1D 50 years.
Paula
Great info. Thanks for doing the research.
Kaci Cheeseman
Does this same thing occur in non-diabetics, or just diabetics?
Christel Oerum
People with a functioning pancreatic system should not see spikes/crashes since their system will manage it for them. For example, during activity, their pancreas will reduce the amount of insulin available so they don’t experience low blood sugar. That’s why we who live with diabetes have to try and mimic a healthy pancreatic system in order to reduce the risk of high and lows
Brian
I have type 2 diabetes. I generally walk or do a lite jog to lower my blood glucose and it works really well. That being said, I decided to do some HIIT training today (out of boredom and to see how it effected my BG) and when I got back from it I checked my BG and it spiked really high. I was shocked at first, but then figured that my muscles or liver dumped glucose to possibly keep up with the exercise. I’m a chiropractor and functional neurologist. So naturally I got online to do some research and found your blog. Thank you for the post, it backed up my thinking. I look forward to following your info.
Christel Oerum
Thanks for the note. Nothing like a little HIIT to keep it interesting 🙂 I’m glad you didn’t get discouraged by the high BG, but could rationalize and confirm the reason here. Keep up the good work
Greg
Hi Im a recently diagnosed type2 diabetic, my Primary doctor has not been helpful so Ive been doing alot of google and I love this article! But I was wondering Is the spike in BG harmful? If Im at 120BG and I do HIIT and it spikes to 180BG but comes down a few hours later, is this spike something that would be dangerous/harmful if it only happens for a few hours?
Christel Oerum
Hi Greg,
In my opinion that spike isn’t an issue as long as it comes down fairly quickly. But the fact of the matter is that since we live with diabetes we’ll never have “normal” blood sugars and all we can do is our best to keep them in range.
However, I’m not a medical professional and I don’t know your medical history so I would recommend that you have a broader conversation with a doctor. Given your current doctor isn’t much help I’d encourage you to either find a new doctor that is or see if you can get an appointment with a diabetes educator.
Katie
Hello!
I just recently came across your blog and am looking forward to the challenge starting in a few days.
I workout 5-6 days a week and also did a bikini competition a few years ago. I am also T1D.
The research you have here matches my own experience and insulin management w training. However, i find my BGs increase around 1-1,5 hrs post interval or weight training. I have experimented w increasing my basal by 30% for 1 HR w 30 mins left to spare in my workout. Do you have any other suggestions? Since I workout in the mornings, nipping this high early in my day is my ultimate goal.
Thank you!
Katie
Christel Oerum
The research indicates that the increase glucose dump can continue up to 2 hours post your workout, which seems to match your 1-1.5 hr increase. Your training might be cardiovascular enough to combat it during your exercise. I think increasing your basal sounds like a good solution. Alternatively you can try and eat right after (plus bolus for it) I wonder if that would stop the glucose dump, and the bolus would give you an insulin boost.
But with all dosing experiments remember to be careful and make small adjustment so you don’t crash
Bodynsoil
Very interesting post, sharing it to my fitness followers