Where should BG be 2 hours after eating carbs?

I just want to clarify my understanding as I think I may have misunderstood the concept. A while ago, someone indicated in a thread that insulin should take 2 hours to bring down BG while correction bolus will take 4 hours. I think it was you @mohe0001? Sorry I couldn’t find the thread again.

Is the BG after this 2 hours post meal supposed to be back at the target BG? If so, I’m not understanding why it’s 2 hours and not 4 hours. Insulin has an active duration of 4 hours (could be 5 but let’s say 4). If the BG is back down to the target BG after 2 hours, what should I be expecting for the remaining 2 hours? Wouldn’t it continue to drop below target BG? Any insulin left in the body after 2 hours would probably have less effect on BG compared to the first 2 hours but it’s still working isn’t it?

It was me, @tedos.
I’ve never heard a good explanation for WHY its 2 hours in one case and 4 hours in another.

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Yes, but the other key factor is what did you eat. A carb-heavy meal may be fully digested, but a higher protein/fat content can prolong impact to bg. Often handled with extended bolus.


I find with a carb heavy meal, there is no way my BG will drop back down to under 100mg in 2 hours - even if it’s like a piece of bread which is 15g carb. I’ve even tried to super bolus and give more insulin up front but find I have to give additional boluses intermittently if it’s still on a rise after the first hour or so.

That’s why I’m trying to understand why it’s two hours and not the entire duration that the insulin is active for.

If you are over bolusing for meals, then it turns into a 4 hour correction? eh?

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Hard to tell.

But if I over bolus to get it down to target by the two hour mark, I find I still have a tonne of insulin on board for the next two hours. So even if I turn my temp basal to 0, I find that I’ll hypo before I get to the four hour mark.

So if I had a slice of bread and it’s 15g, I bolus enough for 25g, I would peak around 160mg and it would pivot downwards quicker - it may get to 100mg in two hours but it’s a free fall to hypo land after that because I have too much insulin stacked. If I had bolused 15g, the spike would probably peak around 210mg and eventually turn around but I’ll need to nudge it with a bit more insulin and it would take 4 hours to come down but I don’t get into a hypo state.

I’m not sure which approach is correct as what I’m seeing doesn’t get me a good outcome with either approaches.

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What short term insulin are you on? Crap. I don’t know if we ever asked you that.
You on some wild old timey insulin? I bet you are.

The 2 hour and 4 hours timings are for Humalog. Your not on Humalog are u?

I’m on novorapid , I think it should be the same as the humalog timings.

But yeah I struggle with post meal spikes and bringing it back down. Prebolus helps but not enough.

Interesting. I started experimenting with pre bolus. Somewhat of a pain but 40m before I eat I bolus 35 percent of what I think I’m eating. Best example is a bowl of cereal which we all know is high in carb especially harder to bring down in the morning. Right before the meal I calculate the carbs and give my normal dose. Seems to me I’m benefiting from less peaks in my BG in those hard to control times. Anyone else try? I assume if you are on a faster acting insulin like that fiasp this is a mute point.

Here is a good summary and chart.


I feel like this 2 hour/4 hour thing is old Diabetes theory still lingering. It’s only in VERY recent years that the common Endo is believing you can stay in range post carbs. Joslin and other diabetes innovators aside. It’s also only in recent years that we’re starting to evolve away from the carb-heavy food pyramid guidelines. Heck, we still see posts often here about “my endo/nutritionist/DE/fill-in-the-blank” says I need to eat more carb".

The common doctor catering to diabetics is so scared of lows, that they EXPECT us to be high and out of range in the post-prandial. Within two hours, though, the bolus should have you back in range. Not necessarily at your target BG, just in range. “Excellent management” used to be defined as obtaining 140 mg/dl (7.8 mmol) within 2 hours of a meal.

I have the 5th edition of Pumping Insulin (2012, I think 6th is the most recent), and I feel like it is already largely outdated. This is an image from the chapter about corrections:

You can see that the Goldilocks “just right” correction factor brings you down over the course of 5 hours, but should be leveling off around the 3-4 hour range.

In that example, the “too low” value still took them 3 hours to get back down to 100, but it’s too fast, because they’re going to continue dropping beyond that. 3 hours feels like a lifetime of elevated BG to me! But that was before we had options to suspend basal.

Now, we’re seeing a lot more options to tightly control the numbers. Low carb/moderate to high protein and fat diets, high carb/low fat diets, greater availability of CGMs, looping, commercial pump semi-closed loops, super-bolusing, etc…

We’re in a great transition where 100% TIR is actually becoming achievable WITHOUT increased risk of severe hypoglycemia, but all the terminology and medical professional mindset hasn’t caught up yet. I think it’s why there’s so much confusion now. We’re really striving for perfection. We want the BG right back at target as soon as possible, and we forget that it was never even expected just a few years ago.


One thing that’s designed to help with the spike situation you’re describing is to use an extended bolus (assuming you’re using a pump), so the insulin’s effect curve is more spread out. Another is pre-bolusing, vs “super bolusing” (though I definitely do that too). It just does seem to be the case that it’s harder to chase down a BG that’s already getting ahead of the insulin than to get ahead of the carbs to begin with. That should help with getting your peak to arrive somewhere in the 140-160 range rather than 200+.

But another thing is a kind of pet peeve of mine, especially dealing with endo’s who are schooled in the literature but not living with the disease themselves. Which is that all these numbers tend to give a false sense of precision, like there’s some reliable formula for manually operating a system originally evolved to be governed by webs of biochemical feedback loops. It’s not like the numbers aren’t helpful as a general guideline, but they’re never going to exactly match what you experience in practice. For me, getting a “soft landing” after a high-carb meal in a reasonable amount of time is a combination of past experience working in concert with what my CGM is telling me in the present, and creating a kind of informed-intuition feedback loop in realtime. Because bodies are all different, not all carbs are the same, and other variables like stress can play a role. So knowing what the rule books say is a good place to start from, but in the end it’s always going to be an empirical process, not a cut-and-dried mathematical one.


What the heck is Novorapid? IDK.

Good point and a very informative post, as I have come to expect from you @Robyn_H. One thing I want to mention—and I know not everyone is a fan, but—Jardiance. It’s off-label for T1, but my endo started me on it about 2 years ago and it has had a huge effect on limiting my peaks and valleys, and dealing with the issues that are the subject of the OP.

No side effects I’ve ever detected, and since I started on it I’ve had A1C’s below 6.0 for the first time in 37 years with T1. It seems to have a general, overall effect of attenuating my BG curves, so that they’re oscillating within a much tighter and lower range over all. Way more useful in that respect, with much less aggravation, than what I found when I tried an AID system (670G).


The ideal post-prandial blood glucose levels for comparison occur in healthy non-diabetic individuals. Now, I recognize that we do live with diabetes and this comparison may seem unfair, but I think it helps illuminate just what the ideal should be.

In this NIH study, Continuous Glucose Profiles in Healthy Subjects under Everyday Life Conditions and after Different Meals, they showed what the CGM trace after meals looked like.

In non-diabetic people, the post-meal trace average rises just above 120 mg/dL for breakfast and just under 120 for lunch and dinner. Following all three meals, the BG falls to under 100 mg/dL at two hours. (IG=interstitial glucose)

Insulin acts during the 5-6 hour period after sub-q injection, whether its injected for a meal or for a BG correction. Its action is weighted in the early portion of that time. Two hours is an arbitrary time-mark that some use to aid analysis.

It might seem unfair to compare people with diabetes to non-diabetics but I think knowing what the ideal is can help us. If we’re going to shoot for a target, I think it’s helpful to aim for a beneficial one.

With limited carbohydrate diets (or high carb, ultra low-fat), adequate pre-bolusing, consistent daily exercise, and an automated insulin dosing system, I think it’s possible to approximate the post-meal blood glucose levels of non-diabetic people. In fact, many adherents of the Bernstein protocol consistently achieve this goal using multiple daily injections.

In the graph, you can see the 2 standard deviation traces above and below the average or mean. Since so many non-diabetics are not metabolically healthy, these excursions provide an interesting comparison. It seems people with T1D could reasonably produce post-meal traces within these limits.

In the ideal, I seek to limit post-prandial BG traces to 140 mg/dL at one hour and 120 mg/dL at two hours with a drop to below 100 mg/dL soon after. I can often do this.


Great explanation. I’m curious what the graph looks like for others when they eat and bolus for a slice of wholemeal bread. I guess the thing I’m trying to work out is is my pattern “normal” or have I got something wrong (be it bolus, basal, correction factor). I did ask my DE and she basically said I’m doing well with my control with my latest Hb1AC and TIR and not to get too hung up about the post meals. But that’s like a typical response for a DE that doesn’t have diabetes, inside me I’m thinking it’s these post meal control that I’m battling with all the time, and I would like to get to the bottom of - be it that I’m doing something wrong or have the wrong expectations.

I’ve tried both actually, I find that the extended bolus have very little effect. Maybe its the amount injected every 5 mins is so small its not able to put a dent on a rising BG - and I find with novalog this often happens. If I make the dosage higher for my extended bolus, I feel I’m injecting so much more insulin. If I set my initial dose lower (say 60% as opposed to 80%) to allow for more insulin delivery in my extended bolus, I find my BG shoot up high very quickly, so a very steep incline on the graph. And then I start to battle with insulin resistance bringing down the BG.

Its the same as novolog just a different name here in australia.

I think you are right, it probably comes from a non diabetic pattern and probably is the best target to aim for.

For this, I think we should be comparing apples to apples in terms of food. If this is the graph for a non diabetic who has eaten a full plate of pasta, I’m interested to see what it looks like for a diabetic eating the same plate of pasta. Is this 2 hour mark achievable using insulin? And I mean for most diabetics not just a small minority. If it is achievable, then the 2 hour mark is a realistic benchmark.

For me specifically, I can’t seem to get this 2 hour BG decline back to or close to target BG. It could be the way my body reacts to carbs or maybe my dosage is wrong (my DE hasn’t called out any concerns with my dosage) or a number of other factors .

This is achievable even for me with a protein meal, but I’m interested whether others have any success in bringing down the BG in 2 hours after eating carbs.

I decided 8 years ago that I could not consistently get my insulin dosing correct if I wanted to continue to consume a high carb diet. I knew that I could occasionally get the insulin dose size and timing right but if I miscalculated my overall insulin sensitivity, insulin to carb ratio, or some other unknowable physical x-factor, then I was put into play like some pinball subject to the chaos of a risky and high stakes game.

With the exception of those who eat a high carb ultra low-fat diet, I don’t think T1Ds can eat a high-carb high-fat diet, the Standard American or Australian Diet, and consistently dose insulin well enough to achieve the post-meal glucose found in the non-diabetics in this study.

I was very reluctant to limit the carbs in my diet; I didn’t want to give up bagels and pasta. I thought of these kind of foods as contributing to my quality of life.

Now I wonder what took me so long. I much prefer the metabolic sanity I now enjoy compared to the metabolic mayhem I lived with for far too long. I’m no longer bloated, overweight, with a foggy mind.

Insulin dose size, timing, and attention to many details can only get you so far with regard to post-meal BGs. What you eat is crucial to hitting those targets.

Like I said, I think this can be done on a limited basis but as far as doing this dependably day after day, week after week, without the drama of soaring highs, screaming BG descents and high glucose variability, I remain skeptical.


Unless you are using Afrezza. Unfortunately few insurance plans cover, although discounted offers have made it possible.

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I’ll collect some data for ya’. But, I’ll warn you in advance that I am seeing a LOT of day to day variability in my dosing. So, give me some time to collect a range of results.

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Are we fans of this?
Novolog is Noooo humalog, right?
Can we get him on some humalog? Is there anyway?

Ill run the same toast test with novolog tomorrow night. Tonight I run with humalog.

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