# Food Peak Time?

Question for pumpers... I know that my Carb ratio is 8 to 1 and my insulin sensitivity is 1 to 20 but how do I know when I have a leftover IOB that my carbs have been already processed? Is there a way to know how long it will take for food to peak? I've been playing the guessing game and it's landed me with quite a few lows and unexpected highs as a result.
Thanks,
LTH

Are you talking about the duration of your insulin activity? For most of us it's somewhere between 3 and 4.5 hours but to find out your own personal duration you can just keep track when you do a correction of how long your glucose continues to drop. You will begin to get close to the actual number to use.

But you say "how long it will take for food to peak", so maybe you are talking about when your spike in blood sugar occurs from food? Again, and average time for many of us is 2 hours and that is why we test our post prandial blood sugars at that point. But it can range between 1.5 to 3 hours most commonly. Again the way to see when your spike comes is to eat, then test at one hour, 1.5, 2, 2.5 and 3 and see when it hits its peak before coming back down. Do this a few times to get an idea. The exception to this would be foods that are both high carb and high fat such as pizza or pasta - those can peak much later, 5-6 hours or even more. That's why those foods are problematic for many of us and we have to do a combo bolus to cover them.

If you wonder about insulin lasting 3 hours and food peaking at 2, the answer is that the insulin will continue to bring the glucose down, hopefully to where it started before the meal. So a textbook example would be you eat at 7PM, starting with a blood sugar of let's say 100. At 9PM your blood sugar is 120. Then at 9?30 it's down to 110 and 10 it's back to 100. (Ah, perfect world!)

Zoe hit the nail on the head. The only way to know is to test and keep records.

Unfortunately, our bodies do not always react the same way given the same inputs. I believe that our insulin sensitivity factor is not really fixed. It changes based on exercise frequency and duration, how well we sleep, our emotional health, and other variables.

Any lesson we learn based on personal experience is always subject to updates. We are living science experiments -- observe, question, hypothesize. predict, test, analyze, and repeat.

As Zoe suggested, test various meals and write down what you observe. Data can be obscured when life interferes! You will soon learn how your body responds, BG-wise, to the meals you like to eat.

how do I know when I have a leftover IOB that my carbs have been already processed?

When your BG drops into a low range before your insulin duration time is reached, then you know that either you didn't eat enough or you took too much insulin. Or your carb count was imperfect.

Analyzing the food/insulin match can only be done once you know your basal insulin is correctly set. Any analysis of meal insulin with an ill-matched basal insulin will be incorrect.

Carb to insulin ratios can vary quite a bit. For example, at breakfast I need 1 unit per 7 carbs but at lunch use 1 unit per 22 carbs. Which is a big difference. So if there's a particular time of day that you're running high or low, you may want to adjust your meal bolus accordingly. Keep track of things, as the others have suggested and look for a pattern.

If you wonder about insulin lasting 3 hours and food peaking at 2, the answer is that the insulin will continue to bring the glucose down, hopefully to where it started before the meal
...and it is this asymmetry that has led to the concept of "pre-bolus" and all the various tactics people discuss here to that end.

The idea is to try and have the insulin working hard just before or right when carb digestion peaks BG. For me, Humalog starts to have a measurable effect around 40 minutes after I take it. I see my first measurable uptick in BG from ingested carbs in about 20 minutes after eating. So, I bolus ahead 20-40 minutes from the meal, depending on where my BG is at the time (higher == earlier).

When your BG drops into a low range before your insulin duration time is reached, then you know that either you didn't eat enough or you took too much insulin. Or your carb count was imperfect.
Don't leave out: Or, your insulin duration of action is set too short on your pump, and you've been stacking without knowing it.