Keto and exercise

Hi all,

I’m newly trying out a keto diet, and one of the challenges I’m having is that my BG tanks when I exercise. Any suggestions from other insulin-users who eat super low carb? It’s great that my bg is bouncing around a lot less than usual, but a lovely, flat line at 90 turns into a disaster 20 minutes into a run, even if I’ve turned my pump off in advance. I used to just eat a bunch of carbs before running…


My BG tanks too on my low carb diet if I eat, dose for meal and then exercise. If I exercise first, bolus about 15 minutes before I finish exercise, then eat I stay flatlined. Just something you may want to try.


I recommend that you try exercising when your insulin on board (IOB) number is very low or zero. That would mean several hours after any meal. The IOB calculation that your pump uses should be based on an insulin duration of 5 or 6 hours. Check out this paper by Walsh et al., 2014, about this issue.

Here’s part of the conclusion that they reached.

Widespread confusion exists among clinicians and patients regarding the selection of an accurate DIA [duration of insulin action] setting in a BC [pump bolus calculator or wizard ]. Further confusion exists about how dramatically the DIA setting can affect BOB [bolus on board, aka insulin on board IOB] calculations. It is somewhat disturbing to see how casually patients and clinicians modify a parameter that has a profound impact on their risk of hypoglycemia. Both the importance and accuracy of DIA settings must be clarified to ensure patient safety and success for the large number of people who utilize a BC each day. In this article, we suggest DIA times that may improve safety for those who use a BC to obtain dose recommendations from an insulin pump or with MDI [multiple daily injections].

Many of us who have used pumps for a long time have gone through a period of setting artificially low insulin duration times. I recommend experimenting with setting your insulin duration to a minimum of 5 hours and track how that works for you. I currently use 6 hours for Apidra in my MiniMed 722 pump used as part of Loop and that works well for me – your experience may vary.

In addition, reducing your basal rate to 50% of its usual delivery (a temp basal rate) two hours before you anticipate starting the exercise helps. This is one of those trial and error things. Keeping a written record will help you figure out what works best for you.

Another tactic would be under-dosing for a meal and then exercising when food typically peaks for you. You could also use a reduced temporary basal rate starting two hours before the exercise start.

There are many people here with more comprehensive exercise experience than me. One is @Eric2.


Thanks @Terry4!

@EmilyC, when do you exercise? After meals, before meals, evening, morning, etc?

And can you tell me a little bit about your exercise? Like what type it is and how hard it is? And how frequently are you exercising?

The body uses numerous fueling systems. These are not a “one-or-the-other”, or an on/off scenario. They overlap and compliment each other.

Your muscles store carbs for use - called muscle glycogen. But one thing about keto is that you do not have the same level of glucose available for fuel, and it takes your body longer to replace the muscle glycogen.

Your body can create glucose from non-glucose sources. That is called gluconeogenesis. But it takes a lot longer for your body to create glucose from non-carb sources than it takes for it to just use glucose!

Ultimately, for low carb and exercise, you would want to have a sufficient zero basal before the exercise (if you are on a pump and can turn it off). And also you should exercise later in the day after you’ve had a chance to have a little bit of your food converted. In the morning before breakfast your tank is empty.

Also, exercising every day on keto is harder, because your body is not able to replace glycogen as quickly on a low carb diet. If you are exercising every few days instead of daily, at least this gives your body a chance to replenish. But if you keep dipping into the well daily, your body is always playing catch-up.

A lower intensity exercise is easier to manage, because it can use fat metabolism for fuel a lot easier than a higher intensity exercise. There is a point in exercise where the intensity is hard enough that you just can’t do it without enough glucose. And your body will do all it can to pull whatever glucose it can. You are seeing this with your BG drops!

Another thing that can help is a slower warm-up. For example, if you immediately get into your exercise, your body is going to try and use the quickest fuel source it can. And the quickest fuel source to use immediately is glucose. If you have a slower warmup, your body can use fat metabolism and then that process can be sustained a little bit longer into the actual exercise.

These are just a few thoughts, but feel free to ask specifics.


Thank you both, @Eric2 and @Terry4!! SUPER useful.

Right now I have a completely open schedule (thanks, COVID :roll_eyes:), so my exercise routine is totally variable, and is often determined by when I think my BG is in the right place. For exercise I either jog (30-60 minutes, 10 minute mile) or bike (1-4 hours, 12 mph). My BG tends to drop precipitously during both of these, starting within about 20 minutes, but definitely more during a run than a bike ride. For jogging I’ve even started with a BG in the 200s, 15g CHO and a reduced basal rate starting 30 minutes prior to the run, and still found myself in trouble about 30 minutes in. I haven’t don’t a run yet while eating keto, because I’m scared! But I plan to give it a try today…

What you said above about slower glycogen replacement, @Eric2, is news to me, and definitely an important thing to know. I’ve gotten lazy during COVID, and am not exercising as much as I used to (despite having so much more free time), but in “normal life” I usually exercise about 5x/week, so that’s something to ponder…

So today I’ll shoot for a run later in the day, and will turn OFF my pump in advance to attempt 0 IOB (really good point, @Terry4, about insulin duration time. I’m sure that’s one of my problems here). I’ll let you know how it goes!

Again, thanks so much for the info!


YDMV! My BG tanks during exercise only when I have to take larger meal time bolus’ to cover carbs…if I’m low carbing, I use hardly any insulin in comparison, and exercising is a piece of cake. BUT, I love carbs and hate low carb eating! I keep trying, but haven’t found a way to eat low carb long term as of yet!

Forgot to add…when I eat low carb, I usually take a tiny bolus, and time my exercise (I have an elliptical and exercise bike at home) to right after eating. This all (FOR ME) = smooth sailing.

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OMG, @EmilyC it is SOOOO nice to see you around! How are you doing? :kissing_heart:

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@anon28090080, it may be that I’m going to have the same experience! Because of course, now that I was so concerned about my usual exercise drop, and did all I could to avoid it, while still avoiding carbs, yesterday when I exercised my BG actually ROSE. TOO HIGH. I should have known; it wouldn’t be diabetes if it did what I expected!


I went for a 30 minute run yesterday, and of course what happened in my BG is the opposite of what usually happens. Ah, diabetes keeps it fun.

So here’s what I did, and what resulted, and if anyone has any suggestions I’d be very glad to hear them:

  • Turned pump (Control:IQ) to “exercise” mode 2 hours prior to exercise. This sets my target BG to 180 instead of 110. BG was 170 by the time I was ready to run (yay!)

  • Turned pump OFF 20 minutes prior to exercise, and kept it off for the first 20 minutes of my 30 minute run

  • Turned pump back on and changed from “exercise” mode to normal mode (target = 110) 10 minutes prior to ending my run

Result: BG 170 when I began to run, rose steadily while running, ended the run at 230 and STILL RISING. Ugh. No carbs involved at any point in the day prior to running. Gluconeogenesis killed the cat? Maybe, as @anon28090080 suggested, I needn’t be so aggressive about removing all insulin and starting with a higher BG prior to exercise if I’m in ketosis?

Any suggestions would be much appreciated!

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The coarsest analysis of any insulin treatment regime is whether too much or too little insulin drives the outcome. In your attempt to avoid exercise-driven hypoglycemia you went from a previous insulin-rich (led to hypos) treatment to one that is now insulin-sparse (led to hypers).

This is good to know! You’ve now bookended your problem with both extremes. Now you just need to methodically and incrementally back off on the “reduced insulin levers” you employed yesterday while keeping the other variables constant.

You could, for example, adjust your Control-IQ exercise mode target from 180 down to 150 which should increase insulin during this time with all other factors being held equal.

Through trial and error you should be able to identify the optimal setting for these insulin quantity levers. It’s been my experience that there is a level and combination of settings that will work for you.

As you well know, however, diabetes is fickle and your discovery of “optimal settings” for this exercise challenge will likely drift over time and that means you must pay attention, notice, and act to drift along with the fickle nature of diabetes.

I’m a big fan of keeping a written record during this kind of troubleshooting. It will help from getting confused as you try various scenarios. You don’t need to commit to record-keeping forever, just until you wrestle this problem to the ground. It’s a great personal teaching technique that will make the details more “sticky” in your memory.

Personal experimentation, journaling, and persistence will allow you to solve this problem. Wash, rinse, repeat. Iterating on this one scenario while making key adjustments is what makes a solution possible. Each “failure” gives you more information to use in the next test run.


I am not a big fan of the pump algorithms for exercise and the adjustments that are automatically made by pumps. Because what is happening is that the pump is doing all kinds of adjustments to your basal for 2 hours, and you don’t really know what is being done (unless you go into the pump records to look at every single adjustment).

And having a starting BG of 180 really saps your strength.

When your BG is too high, you can’t burn fuel for the exercise, not even fat metabolism. Your body can’t use blood glucose for energy (no insulin to process it). It can’t use liver glycogen for the same reason. And it can’t even use fat metabolism efficiently.

I would suggest trying a different approach.

If your BG is around a flat 120 leading up to the exercise (I think that is around where the Control-IQ target is), start with simply turning your basal off for 30-45 minutes before exercise and leaving it off while exercising.

If your BG is lower, maybe do it 60 minutes before. And if it is higher, maybe 30 minutes before. Just use the BG as an indication of how long you need to turn your pump off.

Manually doing adjustments to your basal lets you know what is being done, and lets you make changes as you dial it in better.


Thanks @Eric2! I’m excited to try your suggestions :slight_smile:

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I love the enthusiasm, @Terry4! Thank you for that. I tend to be a lot less positive about the process (as in, “damned either way”), and your view of it is tremendously helpful. Not to mention your great suggestion to actually KEEP TRACK!!! MAN! I do struggle to do that.

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If you exercise under an hour, on eating only 2 or 3 carbs a meal, 4 tops, 30 min to 60 minutes would help both drop weight, or lower B. G. If you are a strict eater, you can carry carbs, or eat little more early. Do you use GGM? On days exercise, try some carb food, one carb. ( 15 grahams) or 1.5 C arbs

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Hi. I’d also lower your basals at least an hour or so before exercising and let that lie basal for an hour after. That ends to work for me. The other thing you can try is actually eating during your cool down. A protein/carb meal.

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I eat low card/keto. I workout every morning on an empty stomach before breakfast. I hardly ever go hypo. I do set my pump to exercise mode and even on the days I do long spin classes (90 mins) my bs only slightly increases.

That being said, I know we are all different, and workouts vary. Just wanted you to know what works for me.