IC ratios for big meals

I don’t use IC ratios and correction factors and ISF and things like that. But I am curious what people see when using IC ratios for larger meals.

Here is my thought:

For many people, correction numbers aren’t linear. Because of insulin resistance, they may find that the correction for 250 would not use the same factor as a correction for 150.

Also, for many people IC’s change based on the time-of-day.

So it seems reasonable that a person’s IC’s might not be the same for a small meals versus a large meal.

For instance, if you were following straight IC recommendations, and your IC was 1:15, if you ate 30 grams it would be 2 units. But would 150 grams be 10 units?

Personally I don’t think it is a straight multiplication. I think there are some “other things” that come into play for large meals that need to be considered.

Curious what people who use IC ratios find with big meals. I have some theories about why it might not be linear.


Oddly enough, a larger than typical number of carbs requires less insulin than would be expected with a linear I:C ratio.

Using the Dexcom has been a terrific way for me to verify this practice!

Yes, I’m with you so far…

Any thoughts on why? I have some! But I want to hear yours first. Let’s see if we come to the same conclusion individually.

I really didn’t know and always found that confusing. My best guess is eating too much and a portion of the nutrition passes through and does not get absorbed.

We actually don’t use an IC past a certain point. For instance, if Samson eats more than 25 to 30 grams at any time other than the morning, we bolus for about 0.6 to 1 units of insulin upfront, and give either the rest or some fraction of the rest about 1.5 hours later… Usually it’s less total insulin.
Whether we give less than what should be predicted based on IC or more than what should be predicted based on IC has largely to with whether there’s a lot of fat in the food.
So pizza takes more overall insulin than IC would predict, but with 0.6 upfront and the remaining + a bonus bump 2 to 6 hours later.
Sweet things often take less total insulin overall than would be expected.
Whole wheat pasta takes right about the IC in total, but broken up in two segments.

I have two guesses.
a) You actually become more sensitive to insulin once your body registers that carbs are plentiful and available, assuming fat content remains constant and is fairly low.
b) You need a flat amount of insulin to suppress the liver dump of glucose initially in a meal, whether you’re eating 5 g or 50 g. Let’s say its 1 unit to make numbers nice and round. If your “true” IC ratio is 1:10, then a meal of 50 grams would take 5 units + 1 unit to suppress liver dumping. A 5 g meal would require 1 unit + 0.5 units for the food. The effective ICs you’d see then would then be: 1:8 and 1:3 respectively.
What are your thoughts, @Eric?

I’ve been experimenting with insulin stacking during and after big meals, similar (but nowhere near as aggressive) to Chap 14 of Ponder’s Sugar Surfing book. For me, big meals are usially at a social event or holiday meal so carb counting is a WAG at best. These types of meals are also the only time I find myself eating a sugary dessert.

Mixed results so far but have not caused any lows and I am convinced this has dampened down and shortened the long uncorrectable highs that can occur from a big meal. Basic method I am trying these days is up my pre-meal bolus by only a few units regardless of meal size, and start stacking before dessert. Continued pre-emptive stacking after the meal with an eye on the CGM at about 1 hour intervals until the CGM says I’m trending flat or downward.

I really only look at IC ratio as a historical statistic rather than a hard and fast mathematical rule.

A nice thing about xDrip+ is that I can look at historical IC ratios for each day and see how the day’s boluses worked out in relation to carbs eaten and pre and post prandial Bg.

One thing I have found is that a higher IC ratio is required for high carb meals. But at the same time it’s those larger boluses that seem to cause a low four to six hours later, after having controlled the spike after eating.

My solution has been to limit per meal carbs.

1 Like

All these perspectives are interesting, and seem to fit with what I see.

My idea is totally a guess! I’d like to work through this and see what makes sense.

I don’t think a 50 gram meal metabolizes at the same rate as a 200 gram meal.

So the reason it is not linear - again, just speculation - is that the metabolism rate is not the same.

So a typical scenario for me - overbolus and eat a crazy big meal, watch my BG drop low for a few hours, and then if I am not crazy enough to take more insulin despite being low, it would go very high.

Kind of nuts to be in the 50’s 2 hours after a meal, but know you need to take more insulin!

So my theory is just that it takes so long for me to metabolize the big meals, well past the normal insulin duration, that the normal dosing doesn’t work.

The reason I thought of this was because of my dinner a few days ago. I had a pizza for dessert. And I went to bed in the 50’s, knowing I’d be up in a few hours taking more insulin. I couldn’t take more insulin at mealtime - I was low after dinner as it was! And my pump doesn’t allow a delayed bolus, only an extended bolus. So I couldn’t set a bolus for 4am. I just had to wait for the spike that I knew was on the way. It was totally predictable. And it made me think that maybe it just takes that long to metabolize giant meals.

What do you guys think?


I think you’re right.

So how would you preemptively prepare for a spike when you are currently low?!

I might go back to using NPH for something like that.

1 Like

I’d time it like 20 times, figure out the average time till next bolus and then set an alarm for that time. if I was on top of things enough for that. Which I’m usually not.

1 Like

This is what I face many nights. Decent-looking rise after my dinner, nice drop towards target a couple of hours later, or maybe even on the low side, but I’ve learned not to treat that low because sure enough, around 2 a.m., my Dexcom is going to let me know I’m high. At which point I almost double the suggested correction, and usually wake up fine. It’s a nuisance, and I’d LOVE a delayed bolus feature. I’m not sure how to pre-empt that second rise. I already deliver my dinner bolus in two if not three instalments, and I need to experiment with a longer extended for that last instalment (usually dessert, given at around the time the main-course Humalog is getting aggressive), with a higher IC ratio than normal for that time of day. A higher basal for a spell might work, but it’s not every night, and it’s not tied to particular kinds of food, as far as I can tell.


The best thing I can figure for something like that is NPH. Thinking through the possibilities, it seems that NPH is the only delayed bolus insulin there is.

1 Like

Agree when it comes to onset time, but it maybe hangs around too long for this kind of scenario. I’m thinking it would still be at work, though weakly, when a person is taking a breakfast bolus, which would complicate things.

I always liked it for helping me avoid morning spikes! Sometimes I would take just 2 units around midnight for that reason.

Maybe the old-timey R insulin could be used for the delayed bolus? That had a slower onset.

The old timey R will last you about 8-10 hours, so it would probably work well for this. NPH will last up to 20 hours.


I actually like this solution. I am a huge fan of alarms.

1 Like

I never got 20 hours out of NPH!

I think I will try some of the old R. Supposedly no prescription needed, and only $25.