If your first reaction to “intermittent fasting with type 1 diabetes” is…”Oh my gosh, my blood sugar would be so low! I could never do that!” …then definitely keep reading.
In this guide, I will cover everything you need to know about intermittent fasting with type 1 diabetes:
What’s the point of intermittent fasting?
There are 3 general reasons a person might want to pursue intermittent fasting.
- Weight-loss: This is the most obvious and most common reason to give it a try.
- Simplicity: Reducing the number of hours each day that you have to think about food, track food, make decisions around food, and cook food can be really freeing! Instead of frantically and unexpectedly skipping meals because of a hectic schedule, intermittent fasting allows you to properly and methodically skip eating during parts of the time.
- Energy: Once you get going, and you’re no longer freaking out about, “How hungry will I feel!?!”…this approach to eating can actually give you quite a boost of energy because your body will be burning fat for fuel instead of relying on sugar from your blood. Body fat is an endless source of energy.
Before we get started: if your blood sugar drops just because you don’t eat for a handful of hours, you’re taking too much background/basal insulin via pump or injection. Talk to your CDE or primary care doctor about “basal testing.” (Or check out Gary Scheiner’s book, ‘Think Like a Pancreas’ and do the basal testing yourself!)
Basal testing literally consists of purposefully skipping a meal (or two) in order to see if your insulin keeps your blood sugar steady, or if your blood sugar significantly rises or falls out of your personal goal range. If it rises, you’re not getting enough background/basal insulin. If it falls, then you’re clearly getting too much.
How intermittent fasting works
When you wake up with an in-range blood sugar (ideally between 70 to 130 mg/dL as a person with type 1 diabetes…the 130 mg/dL being on the higher end but offering some room for imperfection in a complex disease) and you don’t eat breakfast, which means you don’t take a bolus of insulin, your body will continue to burn fat for fuel because you have yet to introduce actual fuel. You have yet to turn on that switch telling your body to rely on glucose for fuel instead of fat.
The moment you eat or drink something containing calories, your body says, “Alright! Now it’s time to burn glucose!”
What an intermittent fasting schedule looks like
There are a lot of different ways you can approach fasting, and after doing this for several years on and off, I’ve found I can flexibly create my own approach that feels most natural to me.
Here are 3 of the most popular fasting schedules, adapted from Dr. John Berardi’s guide to intermittent fasting:
- 24-hour fast: You eat dinner on Thursday (for example), and then you don’t eat again until dinner on Friday. This should generally only be performed once per week. (Read Dr. Berardi’s guide to see what happens if you do a 24-hour fast too often.)
- 16-hour fast: You eat dinner on Thursday (for example), and then you don’t eat again until 1 or 2 p.m. the next day. It’s important to note that you should still eat a normal day’s worth of calories during that 8-hour eating window. If you’re trying to lose weight, that amount of calories might only be 1200 to 1600, but you still need to get your calories while following a fasting program.
- Periodic fast: You suddenly decide to go 24 hours without eating, unrelated to your fasting or eating schedule throughout the rest of week. I like using it when I know I’m going to be eating a really heavy meal (Thanksgiving, holidays, pizza or Chinese food, etc.). I’ve also used this when I know I’m going to be sitting in a car for a long time on a road-trip, or if I know I’m going to be somewhere new with my kids and I really don’t want to risk any low or high blood sugars – I just want to remove diabetes from the equation altogether so I’ll fast as long as I can that day.
If you search the web on intermittent fasting, you’ll find there are people who emphasize that fasting for weight-loss needs to coincide with very clean-eating and attention to nutrition, while you’ll find others who say they fast all day and then eat pizza every night.
If you’re trying to lose weight, you’ll really want to lean towards the clean-eating and attention to nutrition (with treat-days planned of course, for long-term success and adherence), but if you’re trying to maintain your weight, I think intermittent fasting offers a lot of wiggle-room for less healthy eating.
During the holidays, for example, I let my eating choices slide quite a bit compared to my normal routine, but I was still following a 16-hour or 24-hour fasting schedule most days of the week, so I didn’t actually gain weight beyond a little carb-laden bloating and water retention.
But won’t I be hungry?
Guess what, it’s okay to be a little hungry. After you stop freaking out about your belly not feeling full 24/7, and push through it around 10 a.m., you might actually notice that you feel a little bit awesome. A little more clear-headed, a little more focused, even a little more energy.
Drink some water – it’s good for you anyway – and embrace that feeling of your body just being empty. Yes, there are many ways to lose weight by eating every 3 to 4 hours, but that’s not the only way to eat, and it’s not the only way to lose weight.
Are you someone who is always thinking about their next meal? Always snacking?
As Dr. Berardi explains:
“Intermittent fasting can be helpful for in-shape people who want to really get lean without following conventional bodybuilding diets, or for anyone who needs to learn the difference between body hunger and mental hunger.”
But if you’re an athlete or intense exerciser...you might simply find that you really need that morning fuel because of your athletic pursuits! That’s okay! That just means intermittent fasting isn’t for you.
But isn’t eating breakfast really important?
Eating breakfast can absolutely be a crucial part of weight-loss and maintaining a healthy metabolism, but it’s not the only way, and more recent research has really diminished how important breakfast really is.
“There haven’t been any conclusive studies that found eating breakfast to have a positive effect on weight loss or weight maintenance,” explains sports nutritionist and registered dietician, Leslie Bonci, as reported in Popular Science.
Also, the idea that skipping breakfast causes weight gain is over-simplified and very false. It’s not the act of skipping breakfast that can cause weight gain, but that in those studies it’s observed that a large majority of those who skip breakfast also lack other healthy habits overall.
“It could be that eating breakfast is simply a marker of a healthy lifestyle and, in itself, doesn’t protect against obesity,” explains Science Alert.
“Several randomized trials (where people are randomly assigned to a certain behaviour, such as eating breakfast or skipping breakfast) have not found any evidence to suggest that skipping breakfast causes weight gain. Despite the association between skipping breakfast and weight gain, experiments specifically designed to try and establish cause and effect haven’t provided evidence that skipping breakfast causes you to put on weight.”
How to do intermittent fasting with type 1 diabetes
As a person with type 1 diabetes, you might even notice that you feel…a little free, because you aren’t worrying about whether you’re going to be high or low after your breakfast.
The awesome part of this for people with type 1 diabetes is this: your blood sugar is steady, steady, steady all morning long until you end your fast by eating at 11 a.m. or 2 p.m. or dinnertime…depending on which fasting schedule you follow.
I’ve also found that if I do a 24-hour fast before a carb-heavy meal like pizza, I’ve found that fasting actually cuts down significantly on the insulin I need for that meal.
If you stick to your fasting program consistently, you’ll find you lose weight and you gain insulin sensitivity, which means: you’ll need to decrease your background/basal insulin rates! This is a good thing! This is part of weight-loss with diabetes, but if you aren’t expecting it, you’ll be annoyed and frustrated with the low blood sugars.
How to adjust high or low blood sugar when fasting
Waking up with an in-range blood sugar is extremely helpful, but obviously, we’re not perfect and things happen. Here’s how to manage your plan for fasting if your blood sugar is not in your ideal range when you wake up:
- If you wake up a little high, sure, you can take a reduced correction dose (read ‘Think Like a Pancreas’ if you don’t know your own correction dose), and carry on with the fast, but introducing that bolus of insulin could be enough to switch on your body’s need to burn glucose for fuel. (For legitimate “dawn phenomenon” high blood sugars, you may simply need a bolus correction of insulin every morning that really is part of your “basal” insulin but is applied via pump or injection as a bolus. If this prevents morning fasting highs, it’s part of your fasting regimen!) *Read more about managing “dawn phenomenon” here.
- If you don’t take that correction dose of insulin, then you’re just spending the next several hours with a high blood sugar…which is counterproductive if our overall goal is health…right? So definitely take the insulin you need in order to be at healthy blood sugar levels–that’s your first priority.
- If you wake up low, then you obviously have to eat and fasting is no longer going to work. You’d be better off eating a healthy breakfast, fueling your metabolism since it’s already burning glucose for fuel, and trying again tomorrow.
- If you routinely wake up with blood sugars that are too high or too low, you need to go back and do some basal testing or test your insulin-to-carbohydrate ratios that you’re using for the food you eat before bed.
- Or this sneaky blood sugar problem: You need to stop binge-eating late at night. If you’re currently up at midnight eating yourself out of house and home, focus on this first before pursuing intermittent fasting. People often blame high blood sugars in the morning on “the dawn phenomenon” when it’s actually the result of late-night binge-eating.
It’s not a magic trick. It’s not a fad. It’s just basic science of how the body responds in a fasted environment.
Exercising in the Morning When Fasting…Is Actually Easier!
When you’re fasting during your exercise, your blood sugar isn’t going to burn up and drop–this is a good thing! Exercising while fasting (which means you did not just take a bolus of insulin for food or a high blood sugar) is easier because your body will burn body fat for fuel instead of glucose. I didn’t believe it either when I first learned this from the bodybuilders at my gym many years ago, but it works.
You will find that with weight-lifting or other anaerobic workouts, your blood sugar will possibly rise during a fasted workout, which means you might actually need a bolus of insulin for that type of workout. This will not take away from your fasted efforts, it simply helps use the glucose that’s being generated from the glycogen in your muscles being broken down due to your anaerobic workout!
I LOVE fasted cardio! In fact, I make sure that all of my exercise sessions happen either fasted in the morning or fasted in the evening (by not eating anything after 1 p.m. and then getting on the treadmill around 7 pm. This ensures that all bolused rapid-acting insulin is well out of my system. It works. When I used to lift weights, I did find that I needed 1 unit of insulin in the morning if I was doing a fasted weightlifting workout.
So in a nutshell:
- wake up with an in-range blood sugar (or correct a slight high with half of your usual correction)
- begin your workout while fasted
- check your blood sugar halfway through your workout during the first few experiments for safety’s sake
- if your anaerobic workout proves to raise your blood sugar, take half of what you would take to correct that high — but take it when you start exercising to prevent the high in the first place
- if your workout is aerobic (cardio), just continue your workout — you shouldn’t see a rise in blood sugar from aerobic fasted exercise
- check your blood sugar at the end
- shower (thank you)…and enjoy the rest of your fasting
Frequently Asked Questions
Is intermittent fasting safe for people with type 1 diabetes?
Absolutely! But you need to make sure your insulin doses and medications are properly tuned. For type 2s taking diabetes medications that intentionally lower blood sugar, you’ll likely want to talk to your doctor about taking that dose with your first meal versus “in the morning” if you intend to fast in the morning.
For type 1s, as discussed extensively above, your insulin doses should be finely tuned (even if you don’t ever plan to fast) so that you can miss meals and your blood sugar is generally steady and in a healthy range. Adjusting your insulin doses to meet this standard is called “basal testing.” If you’ve never done any basal testing to assess the accuracy of your personal insulin doses, definitely do that first. And do it even if you don’t ever intend to fast. It’s essential to diabetes management.
Again, as explained earlier, during your first week of fasting, check your blood sugar often during your fasting window to see how your body responds. And if you stick with it long-term, you’ll find you definitely will need to reduce your basal rates (even within a week or two) because intermittent fasting has an awesome benefit of…increasing your sensitivity to insulin!
What can you drink during intermittent fasting?
During the time-frame that you’re not eating calories, you shouldn’t be drinking any calories either. Black coffee or tea or water or seltzer (or diet soda, if you must) are all safe to drink. In general, I don’t encourage the consumption of drinks loaded with fake sweeteners. Drinks like Vitamin Water, even the sugar-free version, still contains calories. Read your labels carefully, and if all else fails, ditch the “diet” products for some all natural, chemical-free plain water!
Do you need to do intermittent fasting if you already follow a ketogenic diet?
You’re obviously going to be burning more fat than the rest of us after eating a ketogenic breakfast, but even some of that breakfast will be converted to glucose and require a bit of insulin to digest, so intermittent fasting still applies to keto-folks, too.
Adding fasting to an already disciplined ketogenic diet will definitely help your weight-loss progress.
Just beware, however, that if you don’t already understand how to eat enough on a ketogenic diet, adding fasting to the mix can be a recipe for a binge.
I highly recommend studying and practicing ketogenic eating for a few months before adding fasting to it. It’s very common for new low-carb eaters to eat too little because they are still afraid of eating too much fat. And fat, as you’ve probably heard, is a pretty crucial part of a successful ketogenic diet!
Why I love intermittent fasting as a mom
I can wake up in the morning, drink a cup of black coffee and guzzle some regular ol’ water, then pack our bags and head out the door to the playground or playgroup or the library. I can chase my kids around all morning long and I don’t have to worry about my blood sugar.
If I woke up at 90 mg/dL, I know my blood sugar is still in that zone.
I didn’t have to spend any time making my own breakfast. Or trying to find the time to make my own breakfast. I don’t have to worry about getting real, healthy food into my own belly until we come home from our morning activity, and I get the kids lunch and get everybody settled.
(If you’re not a mom of two children, let me tell you that finding time for your own breakfast is actually incredibly challenging some days amongst the diaper changes and the bottles and playtime and the…on and on and on! When that second kid pops out, parenting is ON in full-power-mode 24/7.)
By 1 or 2 p.m., I’m not starving, I actually feel pretty energized after that morning fast. And making myself a healthy meal feels very doable because the busiest part of the day is behind us.
Should you try intermittent fasting?
If all of the above sounds appealing to you, give it a try!
A few things to keep in mind when trying intermittent fasting with type 1 diabetes:
- Do you currently have a healthy relationship with food? If not, I would address that first. Fasting is not ideal for the yo-yo dieter or someone trying to recover from an eating disorder. Visit We Are Diabetes or check out my book on Emotional Eating with Diabetes or Diabetes Burnout to get started.
- Take good notes! The first week you try fasting, write down the insulin you took before bed, what your blood sugar was in the a.m., etc., so you can pinpoint any diabetes-related variables that are causing lows or highs in your blood sugar during the fasting period. For example: if you’re still up at midnight eating chips and ice cream, you can absolutely bet that will raise your blood sugar during the hours of 6 a.m. to 12 p.m. when you’re fasting. Some people blame dawn phenomenon for what is actually late-night binge-eating.
- During the first few fasts, check your blood sugar often. Even though fasting itself shouldn’t cause low blood sugars, your insulin doses simply might not be accurate! And nothing will reveal that sooner than fasting. Check your blood sugar often and take good notes. Learning how to study and adjust your insulin doses is a crucial part, I believe, of long-term success in life with type 1 diabetes.
- It doesn’t have to be 100% to benefit you: If I wake up and feel really hungry and genuinely feel an intense need to eat, then I listen to my body, and I eat breakfast. If I want to go out to breakfast (once in a blue moon) with my family, then I eat breakfast. It’s not a big deal! Make it work for you. Follow the program as much as you can, and don’t freak out when life gets in the way.
- You may find it useful for a few months, then back to a normal schedule. I’ve found that intermittent fasting has been really wonderful for me for several months at a time. And then I take a break from it for a couple of months, and then I naturally feel ready to follow that schedule again. Listen to your body and find what works for you.
- Be patient. If you fail a day of fasting because you gave in and ate one of those goddamned office muffins, relax. I’m a big believer that creating your own life around nutrition is a very long work in progress. Be constantly open to evolving, learning, trying new things, and never never never shaming yourself for being imperfect. It’s one big science project. Enjoy the project, stop punishing yourself, and learn to love the food you eat. Food can be fun, even when you’re trying to lose weight!
Learn. Study. Experiment. Repeat!
Update: I recorded this video where I talk more about why I do fasted cardio, how I do it, and the benefits. Please let me know what you think in the comments below
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Angeline Clarke says
Thank you so much for this article, which has been so helpful.
I am T1D (42 yrs) on insulin pump and cgm. It has been a constant frustration, since using the pump/cgm that despite clearly spiking when eating, I am unable to get this to a better time in range.
Due to surgery, I needed to fast and decided I would progress IF, after much reading. I generally use 16:8 20:4, but still working out what is right for me. I’m delighted with the improvements after a few weeks with my time in range.
My general exercise is to run, and I want to return to that, do you have any possible information as to the impacts of running, whilst in a fasted state, as I prefer to run when I wake. Normal runs would be 30/60 minutes x3 with longer run at weekend?
Thank you for the priceless articles Diabetesstrong and Dealing with Diabetes burnout, was the best book, I’ve read.
Ginger Vieira says
I hope your surgery recovery went smoothly! I’m a huge fan of running fasted in the early AM. If you’re on a pump, you may find that you need to set a reduced basal rate for at least 1 hour prior to running — some people need a BIG reduction (like 70%) and others need only 25%, etc, so you’ll have to experiment. Personally, I don’t use a pump and I find that my blood sugar RISES in the morning due to dawn phenomenon so I actually need a small bolus when I wake up — like 1/4 units. Then I do my cardio. So, you can see…there isn’t one simple answer to this unfortunately! I would first experiment with the expectation that you could go low. If you rise instead, and see that pattern repeat itself for a few days, then it sounds like dawn phenomenon hormones are at play.
I’ve written more about this here: https://beyondtype1.org/avoid-exercise-low-blood-sugars/
You can also find ALL my writing here: https://www.gingervieira.com/diabetes
Thank you for reading! I’m so glad you find the burnout book so helpful!