Carb ratio

I am trying to help my wife (Type 1) figure out her carb ration. She has switched to a low carb diet this past month. She is on Novolog and tresiba. She has been taking 9 units of the Tresiba each evening and about 1 unit of Novolog for 3-5 gm of carbs.

My confusion is when using some of the standard calculations that is not the number that is calculated. For instance the 500 rule gives the following result.

500/16=31.25 so 1 unit of insulin per 31.25 carbs.

What am I missing?



Well, it’s hard to say based off the info given. First know that the rule of 500 works great, if her long acting rates are right and if she isn’t roller-coastering with hyper and hypo BGLs. Type 1s can end up with insulin resistance after time. How long has your wife had diabetes?

My ideal insulin to carb ratio is 1:10 and I average taking 39 units per day. My dr wants to aim for 35 because I’m experiencing some lows. I’m 40 and have had type 1 for 29 years. When I was in my teens and twenties my ratio was 1:15. So they do change some.

Do you have either “Sugar Surfing” or “Think Like a Pancreas” books? I recommend those for learning how to adjust rates confidently. It’s a complicated algorythim for sure!

Thank you for the reply. She has had diabetes for about 10 years but had gotten “lazy” with her diabetes. She is trying to buckle down and get things under tighter control. I have read the “Think like a pancreas” book but I’ll have to see if we still have it and following its testing advice. I am trying to assist her but also trying not to be a know it all, as she is the one that has to deal with all the oddities that come with diabetes

1 Like

Many people who go low carb need to dose for protein as well as carbs. That could be what is skewing her i:c ratio.

1 Like

We match! :slight_smile:

1 Like

Typically you can’t dose the same way on a low carb diet, as it is primarily protein being converted to glucose by the liver (which takes anywhere from 4-8 hours) and minimal slow-acting carbs that you are dealing with. Typically, Novolog is not the right insulin as its profile will not match the digestion/conversion of protein to glucose on a low carb diet. You could try using Regular human insulin (also called Humulin R, Novolin R, Toronto or Actrapid), which you can buy over the counter at Wal-Mart if you live in the United States, or at a pharmacy almost anywhere else in the world. It has a profile well-suited for low-carb diets.

Not to mention a decent amount of exercise or physical activity will reduce the need for boluses to near zero. Just ask my wife!!

@jwmiller64 truer words were never spoken. Kudos to you!

Thank you all for your responses. Now I have a couple new things for her to try. I will try to let you know how it goes.

1 Like

There is really only one way to find her exact I:C ratio. But first, you need to know her correction factor. Heres how you test:

Find a time where she’s been fairly steady at about 150-180.
Give one unit of Novolog.
Test every half hour for 3 hours. Note the total drop in points. Lets say its 40. You also will be able to see how quickly it starts working (this is helpful info when giving boluses).

Next, you can test her I:C ratio. You will need a small amount of fast acting glucose, no fat or protein i.e. apple or orange juice, a bag of fruit snacks, etc.

make sure to read the label on the juice. If it says 6oz is one serving, take just that. Dont guess.
Take the juice and test every 30 minutes for 1.5-2 hours. Notice the rise at the end. Lets say she goes from 150 to 210. Lets say juice says carbs is 28g.

Now, you know how much one unit will drop her - 40. If shes now at 210, to correct back to 150, thats 60 points. 60/40=1.5 So now you know 1.5u will cover 28g, or to simplify, 1u will cover 19g of carbs, rounded up.

Keep in mind also its common I:C ratios can differ at different times of the day, so you’ll want to test like in the morning and maybe right before dinner.

1 Like


Thank you for the detailed response. In her particular case because of the low carb diet she was needing to bolus for the protein she was eating. That and she realizes that she needed to bolus for feet on the ground phenomenon.

Also some people find insulin resistance increases when low carb, so I:C ratios may also increase, besides needing to bolus for protein.