Competitive Endurance Sports / Marathon with T1D - Insulin+Glucose strategy

I’m an T1D athlete training for several competitions including marathons. I read that a lot of elite athletes have been experimenting with Insulin and Glucose intake to enhance their performance, hence Insulin has been on the banned substance list for Non-Diabetics as it can act as a growth hormone.
It seems like its effects are still not well understood, but I personally made the experience that the right insulin strategy in combination with the right glucose intake can make a huge difference in my sports performance, e.g., my Marathon time improved by almost 2 hours in the last 2 years.
Does anyone have had similar experiences? Is there any further research literature on this topic, e.g. how to determine the right insulin/glucose combinations for best performances in endurance sports?

@gg213 Hi Guido and welcome to the JDRF TypeOneNation Forum.

Yes, insulin is a growth hormone and there is the the possibility that insulin - which you need to still be alive - improved your marathon time over the last two years. I would rather like to believe that your time was improved by YOUR hard work and perseverance - congratulations!

I understand that you need additional glucose in your system as your body is working hard and that you MAY need additional insulin to counteract a high body glucose level but if you overdo the glucose and insulin you may cause yourself harm. This is something you should discuss with your endocrinologist.

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Hi Dennis, Thanks for your response. Obviously it’s much more nuanced than my initial summary and there are many factors contributing to improving athletic performance, including a lot of hard training and perseverance - but also trying out and fine tuning different nutrition and insulin strategies when exercising.

I found though that if I keep my glucose intake constant on a higher level (e.g. at a marathon there is gatorade at every mile plus gels, bananas etc.), and use the appropriate basal/bolus combination to keep the blood glucose level in a normal range (I usually start out in a higher range around 250mg/dL and then it falls and stays around 90-120) I have noticed that i can push out the depletion of the glycogen reserves (i.e. the stereotypical “hitting the wall” effect) further. I also noticed if you keep the blood glucose level too high, then I hit the wall much earlier and the muscles are more prone to cramps. So it’s a fine balance. Would be great if there are additional studies or ways to calculate the optimal insulin/glucose combination when exercising - something more sophisticated than just general recommendations.

Btw, I discussed this with several endocrinologists here in NYC (all of them fairly young and usually familiar with the latest diabetes research) but they all seem to know only the basic facts on this topic and are not that familiar with research in sports medicine or have T1D + endurance sports experience on their own.

I hope people will forgive me for speaking broadly, but I believe most people find that getting the right settings and plan for exercise takes some trial and error. I once read an article suggesting that athletes planning for those type of events (really all of us), should start small and work their way up so they could fine tune their changes over time - this dosage/food combo works fine for ### time, then glucose drops or rises so before moving on to a longer or more strenuous workout… you get the idea. A dietitian can help you with planning meals and snacks for the long haul; and there is a factor called the glycemic index which is a measure of how particular foods affect glucose. Not just how much they cause then to rise, but whether it’s a sharp rise followed by a fall, or a gradual one that will stick with you over time, regardless of carb count.
Congratulations on your upcoming achievement!

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Hi @gg213 and welcome to TypeOneNation. I used to run quite a bit more than I do now and for me it’s just getting that steady state sugar uptake with insulin trick as close as possible. I agree cutting insulin and starting a run over 250 mg/dl and I would cramp and fatigue very fast.

Fast insulin is still in my system at hour 3 and it’s complete pain to try to manage that and have high energy output.

My focus the last 4 months have been strength training and I find reasonable results with cutting meal insulin and basal rates then going to the gym. Since I am only doing a 60-90 minute routine the change in blood sugar is manageable. One interesting thing is I find my body switches to burning fats with less insulin, and while the normals out there have to eat low carb to achieve “keto” I find it easier because I manage insulin. Peaking insulin after weight training is easier I can just put in 2-3 units and then eat to control blood sugar. The insulin spike seems to aid recovery time and supports muscle growth. So far so good but I strained an upper back muscle and am recovering for the last 3 days.

Dr Sheri Colberg is a T1 and has a book out regarding T1 and exercise I don’t have a copy but I am thinking about giving her book a read.

Good luck keep us updated.

Guido @gg213, another thought after reading what you said that the endos you spoke with are not really familiar with your situation. There are a number of running made up of people with diabetes, competing in marathons. Check out the JDRF and ADA web sites - the Events Tab at the top of this page to find a group near you.

I suspect that you can find a group and through that group you may find a research project dedicated to effects of strenuous exercise on diabetes - you could volunteer as part of the study.

Dennis, That sounds good and I will certainly check out those web sites. I did already run the Philly Marathon for JDRF.

Joe, this is very insightful and I will check out Sheri Colberg’s book/website. I also found a website of a T1D guy that is into strength training and has published books and videos on this topic (
BTW I also noticed similar keto effects you described, usually after high-intensity workouts.

Hi. You may find more personal data in the Facebook group “Sporty Diabetic Type 1’s”. Many runners in the group.

Completely anecdotal, and recognizing that I’m basically just bragging on my kid, but in case anyone ever doubted the benefits of exercise:

Our T1D daughter recently completed the “Horrible Hundred,” a very hilly 100-mile bike ride. She’s 11, and she rode it with her dad and a ton of other super-positive people out that day. It’s a great event, and she’s ridden it before on the tandem with him, but this was her first time on that course on a single bike.

(Sidenote: she wore a “Changing Diabetes” Team Novo-Nordisc kit, which she’s rocked in every kids size they sell since her diagnosis five years ago now. Great kit.)

Anyway, it was 8.5 hilly hours of essentially continuous riding, during which she drank Gatorade, and ate oranges, bananas, and granola bars freely.

She’s on MDI, and with her usual basal on board, her BG stayed between 80-120 all day without a single bolus. Not one, all day long. That was her favorite part.

My favorite? At the end of the ride, when she was entering her exercise into the Dexcom. “Was that light,” she asked, “or moderate?”

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Congratulations! I haven’t biked in years so I’m amazed at doing that distance in a day - I am in awe! Congrats again to your daughter and her dad.