The Timing of Insulin Administration: Don’t Shoot Your Wad Too Late!

Dr. E's Case Study

The Patient:

My patient Dale is a 71-year-old male with a long history of type 2 diabetes, diagnosed in 2001. He’s taken all the typical type 2 medications over the years, but with time he became totally dependent on insulin, which is not unusual. He behaves very much like a person with type 1 diabetes, and now needs both basal and fast-acting insulin.

He has an extensive list of multiple medical problems, but most pertinent one is an inflammatory disease called “giant cell arteritis” which is treated successfully with high-dose steroids. Steroids, as you may know, really wreak havoc with blood sugars, and Dale’s A1c went from 6.6% to 9.9% once he started them.

Dale takes 20 units of Lantus (increased from 10 units) daily at night, and 10 to 15 units of insulin aspart with meals and for correction doses (increased from 5 to 10 units). He also takes 1000mg of metformin twice per day, as well as 25 mg of the SGLT2 inhibitor empagliflozin (Jardiance) once per day.

Here’s a Snapshot of Dale’s 14-Day Download from His FreeStyle Libre 3 CGM:

April 2024 case study freestyle libre download

Dale’s metrics clearly show that during the two weeks of the download’s time frame, his average blood sugar was 162, his GMI (or what I like to call “sensor-derived A1c”, thanks to my good endo friend Dr. Ian Blumer in Toronto) is 7.2%, and his glucose variability is 31.6%. All fairly close to a very good goal range. His time in range is 67% with very little lows, leaving 32% (8 hours a day) of his time above 180 mg/dL.

The Problem:

Here’s a Snapshot of Dale’s 24-Hour Glucose Profile:

April 2024 Case Study Glucose Profile

Upon reviewing Dale’s 24-hour glucose profile, he has a  large rise after breakfast (which he eats just before 6am), almost to an average of 250 but often over 250. He also has an excessive rise after lunch, though not as high as after breakfast.

When I talked to Dale about his normal routine, he told me he takes his fast-acting insulin after eating because he thinks it puts him more at risk for hypoglycemia if he takes it before eating. He does the same thing at lunch, and as a result his blood sugar goes high and stays high pretty much the rest of the day.

The Solution:

This is a common but misguided fear. I showed Dale the following data from a study that was done with a group of patients who were given the same meal with the same amount of carbs and the same amount of insulin, but they took their fast-acting insulin for the meal at different times. They all started the study with a blood sugar around 150 mg/dL.

April 2024 Case Study Glucose Timing Study

As you can see from the chart:

  • Group # 1, the diamond shape, took their insulin 20 minutes before the meal.
  • Group # 2, the rectangle shape, took their insulin at the time of the meal.
  • Group # 3, the triangle shape, took their insulin 20 minutes after eating.

The post-prandial blood-sugar rise in Group # 1 went from 150 to 180 mg/dL, but the rise for Groups 2 and 3 went from 150 to 225 mg/dL. Significant difference!

A lot of patients in Groups 2 and 3  would normally have taken a correction dose, but look at the last point on the graph – they all ended up at about the same spot! These folks were not allowed to give themselves a correction dose in the study, which probably explains why a lot of people go low when they correct. You don’t always need to correct – sometimes you just need to wait. The study was done over about four hours. Groups 2 and 3 had a greater time above range and a lower time in range.

The Takeaway:

Many people with diabetes feel that if they take their insulin before eating, they’re at risk for hypoglycemia. However, there’s a mismatch of insulin action and absorption of food when you take your insulin after eating, which leads to a higher rate of hypoglycemia. You can see that in this study. If patients had been allowed to give a correction dose when they were above 200, they would have gone low.

Subcutaneous insulin takes time to get into your system. It typically matches the absorption of most regular meals, so taking your insulin 20-30 minutes before eating is the single most important factor in preventing a post-prandial rise than anything else I can tell you, other than taking inhaled insulin Afrezza.

The hard part is remembering to take it early. If anyone out there can find a solution for that, I’ll be your first patient and we can submit your idea for a Nobel Prize!

Additional Resources:

Post-Meal High Blood Sugars: How to “Strike the Spike”!

Strike the Spike: Controlling Blood Sugars After Eating

Inhaled Insulin Afrezza: An Underutilized Treatment in the Type 2 Toolbox

  1. Avatar

    If you are taking Lispro or Lyumjev 20 minutes early might be too early. I take mine 5-10 minutes early, if I go 20 minutes early I get a low BG.

    • For the vast majority of people, 20 min is actually kind of short, but it all depends on how low your blood sugar is at the time you take your insulin early, as well as your sensitivity. Kudos for figuring out what works for you!

  2. Ian Paterson

    I’ve found setting a 20 minute timer on my watch when I give the pre-meal bolus (Apple watch – others are available) really helpful. And it mitigates the fear of being distracted and forgetting that I’ve already bolused 🙂

  3. Avatar

    I take mine up to an hour ahead, but usually 30 mins. I wait for my BS to be under 150, or chaos ensues! If it takes longer than 90 minutes to behave, I may take another small dose. My BS is absolutely well controlled, with my average daily glucose in the 140s.

    Thanks for a great article!

    • Avatar

      Thanks for this advice. I feel that this best but never had it explained or shared.

    • I’m impressed. A lot of people need to wait longer as you do…keep up the great work!

  4. Avatar

    Great article! I started doing this 2 years ago and it really works. I suggest to use common sense. If your BS bellow 90 before meal, take your bolus right before. It it up 90 up balance your time like 20 minutes before. If is over 150 take 45 minutes before , and if is over 200 1 hour before and wait until BS comes down. It works for me.

  5. Avatar

    Great article obvious but I wasn’t doing it. Guess I was afraid of going low if I took Humalog 20-30 minutes early.
    I tried supposedly faster acting Aspart/Fiasp but found it didn’t start to act any faster and results were more erratic than Humalog. So I’m back on Humalog.

    • The responses from people who try it are mixed. Some people who try it really notice a a difference, and others don’t. It should not cause erratic blood sugars, but your experience is your experience.

  6. Avatar

    I honestly dont plan my meals that far ahead and have taken it 20 min before eating & started tanking before, preventing me from cooking it. I don’t know what the balance is…

    • You should take half the amount of insulin for what you typically eat beforehand, and the rest when you do sit down to eat, so at least you get a little bit in your system ahead of time so you’re less likely to get low because you’re only taking half the amount.

  7. Avatar

    Another plan is if BS is high eat your carbs. Or skip it ! If your sugar is low say below 75, doo your injection late & Eat your carbs 1st.

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