Post-exercise - "wasted" carbs

This topic was recently brought up and I wanted to create a wiki to discuss it.

(It may be helpful to read these first:)
What should I consume before exercise?
How does my body fuel exercise?

So the question was brought up about wasted carbs. When you are done exercising, and you want to restore the muscle glycogen you used, what happens if your BG is high? Those are “wasted carbs”…

Step in to the way-back machine a little bit. From the days of urine testing, all you knew about your BG was if you were spilling sugar in your urine. If your BG is 160–180 mg/dl or perhaps a bit higher, your kidneys begin to excrete glucose in the urine. The sugar is not being metabolized, it is not being used. It’s basically just wasted. You are peeing it away. That’s what I mean by “wasted carbs”.

What does it take for your body to use the carbs you take in? If you have been paying attention for years, and you take insulin, you know the answer…insulin!

So if your BG is high after you finish exercise, and you are trying to restore the carbs, you aren’t doing it. You will just end up flushing those carbs down the toilet.

Here is an example. Suppose you finish at 95. Great! You take 2.0 units of insulin and 40 grams of carbs. After 30 minutes you have spiked to 200…
You know since you took 2.0 units, you got some of those carbs. But the ones that caused the spike are not being used by your body. You need sufficient insulin to metabolize the carbs. You are only able to use the ones below the threshold that caused your spike.

I always try to get a specific measure of carbs post-workout. The way I know for sure that I used all of them is to make sure I have taken a sufficient amount of insulin so that I do not see a spike after the carbs. And any low I have is just met with more carbs.

So a couple of key points:

  1. If you are exercising below a certain intensity level, if you are primarily metabolizing fat instead of muscle glycogen, restoring carbs after exercise is not as important.

  2. If you are only exercising occasionally, and your body has several days to restore muscle glycogen between exercise outings, you don’t need to do it immediately after you finish. You can do it over the course of the next day or so.

  3. But if you want to exercise intensely on two consecutive days - restore immediately.

  4. One of the things that is frequently overlooked by Endos and CDE type instructors - telling you to take insulin right after a workout. That’s crazy talk to them. But if you want to do it right, you need both carbs and sufficient insulin to metabolize those carbs. If your BG is low, then the carbs you take in following exercise are used, and you obviously don’t need insulin. But if your BG is high…you need sufficient insulin to use the carbs.

End of wiki ---------- comments start here


really fascinating Eric! I feel like I’ve learned so much from your posts on exercise.


I’ve been wondering about this. Thanks for clarifying!


This is a little fuzzy to me. But I know you can explain it better, and I’ve read this thread three times now, and it’s JUST starting to make sense that I didn’t understand the above while EH was doing his new exercise program.

I think what you’re going to say is that EH is getting too little insulin to cover the carbs he’s taken in with the recovery drink if he’s seeing a post-run spike.

The confusing part is: how many units of insulin are required to cover, taking into consideration the increased sensitivity to insulin?

Let’s work through it, a little at a time.

After exercise, you want to re-fuel. In order for your body to use carbs, it also needs insulin. Any carbs that you take in - for which you don’t have enough insulin - your body can’t use.

Let’s look at two extreme examples:

  • Suppose you want to take in 500 g carbs after exercise, but you only take 1 unit of insulin. Obviously your body would not be able to use all 500 grams. The limiting factor is the insulin, right? The 1 unit of insulin only covers some carbs, not all. The rest of those carbs end up as high blood sugar, and then your kidneys throw them away when you pee (what I called wasted carbs).

  • The opposite extreme example, suppose you only take in only 20 grams after exercise, but you take 10 units of insulin. All 20 grams will be used, you have plenty of insulin. But you have too much insulin, so your BG will plummet.

So both of those examples are bad. You want to replace sufficient carbs, and you know you need sufficient insulin to do that. So it’s a matter of identifying two things - 1) the correct amount of carbs based on the intensity and duration of the exercise and what you are doing the next few days, and 2) the correct amount of insulin to cover those carbs.

Let me stop there and ask, does all of that make sense so far, and is that helpful? And we can move on from there.



This is effing awesome. Thanks so much for this post. Just referenced it on Twitter as well.


@Eric Yes, it makes sense!

and @mikep I’m so glad someone else found my confusion helpful too!


It’s cool, we are all confused, that’s why we are here!

So the next thing is to figure out an appropriate amount of carbs for restoring, and an appropriate amount of insulin for it…

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And how do we identify or quantify this amount ? Seems there are a wide range of differing beliefs on the subject

It’s likely we can roughly identify how much needs replacing. It is harder to figure how much can be forced into glycogen right after exercise.

But how do we define that “need” ? Some people eat barely any carbs… some people eat hundreds, both are certain they’re doing the healthy thing-- clearly both of their “needs” are being met

Not for exercise. Your body chemistry uses primarily carbs to replace glycogen.

There is an easy way, which won’t exactly be correct, and a much more complicated way which can give you a better idea.

So much of it depends on how soon you need it replaced. I always tell DM to take it right after, and use quick carbs because she is swimming 5 days a week. She needs to replace it for the next day.

But if you are not going to exercise the next day, the hurry is not a great. So a lot of it depends on how soon you need it. If you need it soon, you need bigger amounts, and you need to do it right after exercise. If you don’t need it the next day, you can wait a little while for dinner or a meal. If you wait though, it significantly reduces how soon it comes in. Your body will restore muscle glycogen much faster immediately after exercise than if you wait a few hours.

The amount also depends on the duration and intensity of the exercise. Most of the calorie counters don’t look at intensity. But that is a bad model, because all miles are not the same. Some are more fat based, and require less carb restoration. Some are more carb based.

Here are a few general rules:

  • Are you going to exercise tomorrow? If yes, take in more and immediately.

  • How intense was your run? If more intense, more carbs.

  • Duration? Longer = more carbs

Use this calculator:

Divide calories by 4 to get carbs. Then you can take a percentage of that, from 30%-75%, depending on the factors mentioned above. Longer versus shorter, intense versus easy, daily versus non-daily, etc.

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This is another whole thread. I have a lot to say about that.

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Fortunately for us you are almost never at a loss for words. Even more fortunately, most of what you say is good info.


i find that if i do a moderate to strong 2 hour swim, i need to replenish with 32 gms carbs within about 15 minutes after i exercise. i bolus 50% of that (.8 units based on a 1:10 ratio ( my I:C ratio at that particular time of the day). it has worked perfectly.

however, if i only swim for one hour, i don’t need as many carbs and i don’t need as much insulin. and also, like eric has mentioned, it all depends on how many days in the week i am swimming for. and it has come down from 5 days a week to only 4 days a week; but i rarely swim less than the full 2 hours. (also, take into account that i have been off my pump for 4.5 hours…i need to replenish not just the carbs, but the basal insulin that i missed while prepping for my swim and then the swimming itself; you can’t wear a pump in the water :blush: )


Why do you bolus only 50%? Do you actually eat the 32g carbs? Bolusing at 50% your normal I:C ratio doesn’t spike you?

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after my swim, i am extremely insulin sensitive. i only seem to need 1/2 of what my carbs are; but i drink my carbs and they are low sugar (Nestley Boost Shakes for Diabetics). i drink them within 1/2 hour post swim (as soon as i walk in my front door after i leave the pool and walk home)

eric taught me this trick and it has worked for me for over a year now. give it a try, although YDMV.

hope this helps some. (and BTW, eric has a different system than i do; his system does NOT work for me. Go figure :wink: )


Thanks, @daisymae! You are a lucky one to be so sensitive :slight_smile: I think swimming requires much more energy than running! I am going to check out the Nestley Boost Shakjes for Diabetics. Thanks for mentioning them!

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@daisymae Is Boost High Protein what you get?? It says there are 0 carbs? Is that right? Or maybe the milk ingredients make up for the carbs? Confused!!

Oh, maybe BOOST Glucose Control Chocolate Sensation Complete Nutritional 8 fl oz Drink is the one you get. It has 16g carbs?

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