Fueling and basal reductions for long runs

Hello! For longer distance running-and shorter runs with strength training sessions, I Iower my basal to 20% up to an hour before my workout and, depending on my numbers before starting, will have btwn 5 and 20 grams of carbs beforehand. I am STILL going low most of the time.
I am running half-marathon distance, so not ultra anything, but long runs are about two hours.
I am eating a combo of fat/protein and carb-like a bit of apple with some cheese, or half an english muffin with butter or peanut butter.
If you do a long workout, what magic do you work so that you are not low all the freaking time? Running in the morning definitely works better for me, but running club is in the evenings and working in the morning has to be done.

I do a 50% temp reduction a half hour before I snorkel for a 2 hour time period when I get in the water for a 1 hour swim. I also start out higher than normal so I have some wiggle room. This has worked really well for me. We are all different.

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Do you keep basal at 20% during the run or turn it off? If you are at 20% and still going low, you might consider turning it off completely during the run.

There is a general guideline for runners (I mean all runners, not only those with diabetes) - for runs over an hour, you should try to consume 30-60 grams of carbs per hour.

For long runs, it’s best to try to follow that guideline, instead of just trying to balance your BG with limited insulin and no carbs.

I try to follow that 30-60 gram guideline, and take a bit of bolus insulin for the carbs if needed. But generally I have zero basal during the run.

I go to zero basal right at the start, or a little while before (maybe 15 minutes, maybe 30 minutes, depending on BG). And take some carbs during the run. Also a few carbs right at the start if needed.

For what to eat before, carbs are the best fuel source. A person’s body has plenty of fat for fuel already, so eating it before a run does not provide much benefit. It can slow the carbs down, and that might help. But eating it does not provide an immediate benefit.

There is a trade-off in fueling, between fat and carbs. By carbs I mean 1) muscle glycogen (which is stored carbs in your muscle), 2) the glucose in your blood, and 3) the carbs you have recently eaten.

You can go farther on fat as a fuel source, but not as fast.

The faster you go, or more intense your workout, the more your body will start to rely on the carb sources.

So depending on your intensity, your body may be relying on mostly fat as a fuel source, mostly carbs, or somewhere in-between.

Are you carrying any mealtime IOB? How close to your run is your last meal?

It’s helpful for me to have training runs at least 4 hours after my last meal bolus, to make sure I do not have any IOB.


Don’t wreck you knees! I have already had one knee replaced. After 15 months, it still isn’t quite right. Protect your knees. That means avoiding unnecessary high-impact activities. I know you know this. Take it from someone who is 72 and would like to remain active for much of the remainder of my life–protect your knees. The saying “the knees are the first thing to go” is often true and can be debilitating.

Thanks so much for your feedback!

I am keeping my basal down to 20%, until about 15-25 minutes before I stop my workout-trying to avoid spiking after the workout-another problem if I forget to give a minibolus when I finish. Turning it off completely kind of freaks me out, but I suppose timing the basal to go back on 15 min before with a minibolus might do it. I may try it if I get brave! i have zero IOB for my evening runs. Last night i meant to run long and stopped after 25 minutes-BG 38. uggh.

Yeah, I am taking the fat to slow down the carb absorption, thinking it might help on longer runs. Maybe straight carbs have to be done, though maybe it has to be the zero basal thing that will work. So many variables!

I will check out the link you posted! Thanks!


For normal exercise, hiking, winter sports etc… I have a standard reduced profile that’s 50 percent of my usual basal, and tweak from there as necessary, and now I’ve got Control-IQ and exercise mode… but do also know there will be some carb injested, whether it be liquid or snack.

There are some things that I just take the pump off altogether for. We have a permaculture farm, more for homesteading than profit, and some days the manual labor kicks my basal’s butt. Especially any summer day I’m sweating in the field in full sun. I am ridiculously sun, sweat, and heat-sensitive and my BG will plummet even if I’m not really working hard. No clue why. I swear I sweat the sugar out or something. The locals think it’s funny that I walk around my own “backyard” in a camelback full of diluted coconut water, because I really need the extra carb, when most of the other ranchers/farmers don’t even carry a water bottle.

I loathe running, but I imagine it would yeild the same result.


great news for runners! I remembered reading about this a couple of months ago and tried to include some journal articles, but for some reason I am not able to post the links. There are other articles as well that you can find that support this!

Objectives To evaluate the short-term impact of long-distance running on knee joints using MRI.

Methods 82 healthy adults participating in their first marathon underwent 3T (Tesla) MRI of both knees 6 months before and half a month after the marathon: 71 completed both the 4 month-long standardised training programme and the marathon; and 11 dropped-out during training and did not run the marathon. Two senior musculoskeletal radiologists graded the internal knee structures using validated scoring systems. Participants completed Knee Injury and Osteoarthritis Outcome Score questionnaires at each visit for self-reporting knee function.

Results Premarathon and pretraining MRI showed signs of damage, without symptoms, to several knee structures in the majority of the 82 middle-aged volunteers. However, after the marathon, MRI showed a reduction in the radiological score of damage in: subchondral bone marrow oedema in the condyles of the tibia (p=0.011) and femur (p=0.082). MRI did also show an increase in radiological scores to the following structures: cartilage of the lateral patella (p=0.0005); semimembranosus tendon (p=0.016); iliotibial band (p<0.0001) and the prepatellar bursa (p=0.016).

Conclusion Improvement to damaged subchondral bone of the tibial and femoral condyles was found following the marathon in novice runners, as well as worsening of the patella cartilage although asymptomatic. This is the most robust evidence to link marathon running with knee joint health and provides important information for those seeking to understand the link between long distance running and osteoarthritis of the main weight-bearing areas of the knee.


I was talking to a friend’s new partner at a party a few weeks ago who is T1 (age 40, diagnosed late teens) and an ultra-distance runner (e.g. 100km + events). He is MDI, and said he runs with his normal basal and doesn’t even carry short-acting insulin for a 100km run. He fuels up mostly with energy gels, plus bananas etc at checkpoints, and consumes vast quantities of un-covered fast carbs during a run. If you’re running low, I’d suggest maybe you need pure fast carbs (and more of them) rather than buffering the carb with fats and proteins.
I guess the confounding factor is that his “normal” basal doses would take into account a massive training workload of multiple half-marathon distance (short for him!) runs per week.

My 8yo son was diagnosed just over a year ago and while he doesn’t do long runs yet, we do go on overnight hikes. We often find that for harder trails (e.g. 10km trail with 500m vertical ascent) we need to turn his basal right off, plus feed him lollies at regular intervals to keep his BG in range - we haven’t kept track of exactly how much, but I wouldn’t be surprised if it were 30-40g per hour even with a zero basal. If the trail is downhill we leave normal basal running and he tends not to need the straight sugars, but still gets about 20g un-covered carbs per hour in granola bars, rice crackers etc (as well as loads of almonds, pistachios, cashews) without going high. After a strenuous hike he seems to need reduced basals and IC ratio often for a week or more. We had a 3-day hike two weeks ago followed by a weekend mountain biking just gone, and both basal and bolus insulin are down by more than 30% on what he was running in late January.
He started doing ParkRun a month ago (5km) and we’re still working on doing it in-range. The first one we under-dosed 50% for his breakfast beforehand, and he started the run on BG 8mmol/L (140) double arrows up, finished on 12mmol/L (215) and level. The next time we dosed for more of his breakfast (still under by 20%) and he started on 6.6 single arrow up, topped off at 8 at the 1st km, then fell like a stone and had to walk the next 3km eating jelly beans the whole way. The last run was a bit better, still under-dosed breakfast by 20% but kept him up around 9-10 for the run with preemptive jelly beans at the start line and regular intervals thereafter, but of course he went high on the way home despite bolusing for some of the carbs as soon as we got to the finish line. A better approach would probably be to have an earlier breakfast so he can start the run with less IOB, but I’m not a morning person so clearing the bolus insulin before a 9am run isn’t going to happen any time soon!

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T1 Chris Pennell rugby player, a brief story about him and his daily routine. It is fascinating and he generally doesn’t use much insulin when he eats because he burns it off in practice.

Also another thread here on exercise.

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