How Fat & Protein Affect Blood Glucose

Fat & Protein: the effect blood glucose

Michelle MacPhee
D-Mom, Creator/Co-founder of WTD

For the first several years after our son was diagnosed with type 1 diabetes, I had only a vague idea that fat and protein contributed to blood sugar swings. Along with carb-counting and the glycemic index, understanding the way that fat and protein affect blood glucose has been revolutionary for the way our family manages diabetes, giving us critical tools to deal with post-meal spikes.

“It’s Not Just About the Carbs”

There are six basic types of nutrients contained in the foods we eat:

1. Carbohydrate
2. Protein
3. Lipids (Fat)
4. Vitamins
5. Minerals
6. Water

Since water and most vitamins/minerals have no effect on blood glucose, let’s focus only on the first three nutrients: carbohydrate, protein and fat. Of these, for managing blood glucose we often think first (and perhaps exclusively) about carbohydrates. The effect of carbohydrates on blood glucose (BG) is well-known by those of us living with the diabetes dragon. And while it’s true that the carbohydrate content of a given food has the greatest glycemic impact, it's only part of the picture…


The Impact of Fat, Protein on Blood Glucose

Other nutrients besides carbohydrates impact blood glucose, too. In particular, protein and fat can (and often do) cause post-meal spikes.


Exactly how protein impacts blood glucose is controversial.

What we do know about the effect of protein is that, in individuals who do NOT have diabetes, protein ingestion stimulates endogenous production of insulin (which decreases BG) as well as glucagon (which increases BG by causing the release of stored glucose from the liver); in individuals with type one diabetes, there is no endogenous insulin production, but endogenous glucagon is still produced. The result is that protein consumption may cause a slow rise in BG, which may be evident approximately 3-5 hours later. This rise occurs well after the peak of rapid-acting insulin (which is strongest at 60-90 minutes after delivery), and thus cannot be effectively included with the meal insulin. In addition, most diabetes professionals agree that if you eat much more protein than usual, that is when you are likely to notice the effect on BG, but the exact effect is difficult to predict.

The problem with protein is that we haven’t yet arrived at a reliable, commonly-accepted method for predicting the effect of protein on blood glucose. The Total Available Glucose (TAG) theory proposes that a significant portion (50-60%) of protein consumed is converted into glucose, but the fact that much of this protein-turned-glucose is stored in the liver makes its effect on blood glucose unpredictable. Further, some diabetes professionals, such as Gary Scheiner, assert that when protein is consumed at the same time as carbs (think of a steak and baked potato dinner), the effect of the protein on BG will be negligible, so the protein does not need to be accounted for; on the other hand,when protein is consumed in the absence of carbs (think of a steak and salad dinner), the protein will have an impact on BG and so needs to be balanced with extra insulin to avoid later above-target BG.

So the protein picture is a little unclear. But what about fat?


Unlike protein, the effect of fat on blood glucose is not debated: the ingestion of fat delays stomach emptying and increases insulin resistance, which ultimately results in a late rise in blood glucose. Further, these effects may last for several hours after eating. Diabetes professionals agree that minimal fat is actually converted to glucose; the BG-raising effect is due instead to the changes in insulin sensitivity, not due to the creation of glucose from fat.

To illustrate this effect, let’s consider the results of an experiment conducted by Howard Wolpert¹ and his colleagues using a closed-loop Continuous Glucose Monitor: they compared the insulin requirements of two meals which had equal carb content, but which varied in fat content (60g of fat in the high fat meal versus 10g of fat in the low fat meal). They concluded that “adults with type 1 diabetes require more insulin coverage for higher-fat meals than for lower-fat meals with identical carbohydrate content”. Okay, intuitively PWD already know that. But what’s fascinating to me are the details: on average, the high fat meal required 42% more insulin (!) and yet still resulted in high blood glucose 5-10 hours after the meal (!). So it’s easy to understand that, if additional insulin is not delivered, we can expect blood glucose to be significantly higher after a high fat meal than after a low fat meal.

But why the emphasis on the phrase “on average”? Because, just like all things related to diabetes, fat doesn’t affect everyone the same. In fact, the biggest take away lesson from this study is that there is great individual variability in response to fat. On average there was an increase in insulin requirement with the high fat meal but this effect varied significantly from one person to the next; some people seem to be more sensitive than others to the BG-altering effects of fat. So the only way to know how high-fat foods affect you or your child is to test it out and see. By paying attention to BG after you eat high fat meals, some people know right away that dietary fat causes challenges for them.

What can we do to avoid the high blood glucose spikes that follow fat intake?

Listen to a podcast:

I recently recorded an episode of Juicebox Podcast with d-dad Scott. I love his podcast! He's easy to chat with, super-intuitive with diabetes-care, has great stories, and he lives with the dragon, so he GETS IT! For episode #471 we talked about Five Guys and A&W (yum), making your own potato chips, thinking in pictures (or not), pulling a number out of the air, being exactly where you're supposed to be, and how the fat in foods leads to crazy post-meal spikes... UNLESS you bolus insulin for fat. Here's where you can listen for free:

(Let’s all show him some love with a download and a positive review!)

Apple Podcasts
Amazon Music
Google Podcast
Online: Juicebox Podcast


  • 1.

    Wolpert et al (2013). Dietary Fat Acutely Increases Glucose Concentrations and Insulin Requirements in Patients With Type 1 Diabetes.

  • 2.

    We gratefully acknowledge the information provided by Lorraine Anderson (RD, CDE, Senior Clinical Manager, Animas Canada) and Shannon Cassar (RN, CDE, Alberta Children’s Hospital Diabetes Clinic), which served as the basis for this article. Without you, we might never had experienced this diabetes management revolution! Thank you!

The above information was reviewed for content accuracy by Lorraine Anderson, RD, CDE.