Stevia is a “natural” sweetener (from a plant, but still highly refined) that has become very popular starting about a decade ago.
Since stevia has zero calories, many people like to use it when they’re fasting, to sweeten coffee or tea, for example.
But does stevia break a fast?
For most people, the answer is no, and it’s probably worth using stevia if it helps you get through your fast.
But like any other substance, whether stevia breaks your fast depends on your fasting goals, and on how your body reacts to stevia.
Let’s see what the answer is for you.
What Are Your Fasting Goals?
There are various ways you could define “breaking” a fast.
I think the most helpful way to look at it is this:
If something prevents you from reaching your fasting goals, then it breaks your fast.
Take a moment to consider what your goals are.
Some common reasons to fast include:
- Reducing body fat
- Lowering blood sugar
- Lowering insulin
- Increasing ketone levels
- Controlling hunger
- Stimulating autophagy
You may be fasting for one of the reasons above, or for something completely different.
Will stevia prevent you from reaching your fasting goal(s)?
For the whole story, read on.
Will Stevia Break Your Fast(ing Goals)?
First, a caveat:
Stevia affects everyone differently, so it may take some trial-and-error to figure out what works for you.
Take everything I say with a grain of salt, and always consider your own unique circumstances.
Now, let’s dive in.
Stevia and intermittent fasting / extended fasting to lose body fat
When you fast, your body starts burning fat for energy (since no other energy is coming in). That’s why fasting is a great way to reduce body fat.
Will stevia interfere with fat loss when you’re fasting?
As far as I can tell, there isn’t any scientific research that addresses this question directly.
Personally, I don’t see any reason why stevia would prevent you from burning body fat during a fast.
I think stevia is probably fine if you’re fasting to lose body fat.
Stevia and (intermittent / extended) fasting to lower blood sugar
Blood sugar (glucose) tends to go down when you fast because you’re not consuming any sugar or other carbohydrates.
That’s why fasting is especially beneficial for people with diabetes (or prediabetes), whose blood sugar levels tend to run excessively high.
In this literature review from 2019, some studies suggested stevia may lower blood sugar after a meal, while others found no significant change in blood sugar levels when using stevia.
Mini Case Study:
Recently I did a little self experiment (on the 2nd day of an extended fast) by drinking 2 servings (8 drops) of liquid stevia mixed with water, and then tracking my blood sugar.
Here are my results:
- Blood sugar before starting: 49 (mg/dL)
- Blood sugar at 30 min: 55
- Blood sugar at 60 min: 53
(“Normal” fasting blood sugar is typically said to be 70-100 mg/dL, but mine often goes down to about 50 mg/dL during a prolonged fast. That’s because my body is using ketones for energy instead of sugar.)
Conclusion: I don’t think stevia significantly affected my blood sugar level. The changes are within my glucometer’s margin of error, and the results are also very low.
Based on the available research and my own experience, I would say stevia is fine if you’re fasting to lower blood sugar, and may even be helpful.
Does Stevia Spike Insulin?
The hormone called insulin promotes energy storage in your body.
Insulin goes up when you eat carbs (so you can store the carbs as sugar or fat), and it goes down when you don’t eat carbs (so you can use the sugar and fat stored in your body as energy).
People with (type 2) diabetes or prediabetes tend to have abnormally high insulin levels, and fasting helps bring their insulin down to normal.
Multiple human studies (here and here, for example) suggest stevia does not significantly affect insulin levels.
There is some animal research (using pancreas cells isolated from mice and rats) showing stevia may stimulate insulin secretion when glucose levels are very high (150 mg/dL or higher).
Not only was that research done on extracted animal organs (as opposed to living humans), they also used unrealistically high glucose levels that you’ll probably never see when you’re fasting.
Based on what we know, I think using stevia is fine if you’re fasting to decrease insulin levels.
Side Note: If you haven’t read The Obesity Code, it’s a fantastic book and I highly recommend it. However, the author (Dr. Jason Fung) appears to have made an error when he stated that stevia raises insulin levels higher than table sugar. The reference he cited does not seem to support this conclusion (in fact, it suggests the opposite – see figure 3).
Does Stevia Break Ketosis While Fasting?
Ketones are the alternative energy source that your body makes from fat when you’re not eating carbs.
When you fast, you’re obviously not (or shouldn’t be) eating any carbs, so your ketone levels go up.
The best part?
Fasting will raise your ketone levels a lot more than just eating a ketogenic (low-carb, high fat) diet.
I couldn’t find any research on stevia impacting ketone levels, but I doubt there would be much of an effect.
For example, during a recent 5-day fast I used liquid stevia multiple times per day to sweeten tea and other drinks. Despite this, my ketone levels stayed very high throughout the fast.
Based on what we currently know, I think using stevia is fine if you’re fasting to boost ketone levels.
Stevia, and Fasting to Control Hunger
This may be the most important question of all:
Will stevia make it harder for you to fast?
In general, fasting helps control hunger. This is partly because your body has a steady supply of fat and ketones for energy, without any wild swings in your blood sugar levels.
(Don’t get me wrong, you’ll probably feel hungry when you first start fasting, but the hunger gets less and less over time.)
But there’s a catch.
Some people feel hungrier when they take stevia, so it’s harder for them to keep fasting.
For example, Dr. Jason Fung (author of The Obesity Code and several other books about fasting that I mentioned above) has noticed this phenomenon with many of his patients.
That’s why he advises against using stevia while fasting.
Related Post: “Life in the Fasting Lane” Book Summary
Personally, I haven’t noticed any increased hunger from using stevia, and you may not either.
(I did find some research on stevia and satiety, but the test subjects tended to be eating cookies (or something similar), not fasting.)
If stevia makes you hungrier, don’t use it when you fast.
Otherwise, feel free to enjoy some stevia in your coffee or tea. 🙂
Stevia, and Fasting for Autophagy
Autophagy is a funny sounding word that literally means “self-eating”. It refers to when your body recycles old, worn out parts inside your cells.
It’s kind of like “spring cleaning” inside your cells.
Fasting powerfully stimulates autophagy, which ramps up roughly 24-36 hours into a fast.
Stevia has zero (or at least negligible) calories, and no protein, so intuitively it seems unlikely that it would prevent autophagy.
I don’t believe there’s any research about stevia’s impact on autophagy. I did find some “expert opinion” suggesting stevia probably won’t interfere very much with autophagy.
But no one really knows for sure.
If your main goal is to stimulate autophagy, stevia might be ok, but it’s probably better to avoid it just in case.
If you’re fasting for just about any other reason, go ahead and use stevia if it makes your fast easier or more enjoyable.
What Else Should I Know About Stevia?
Watch Out for Combo Sweeteners
I recently purchased an “Organic Stevia Blend”, only to discover when I got home that the first ingredient was erythritol, and then stevia. Oops.
I guess it was an imitation version of Truvia (which is also a mix of stevia and erythritol).
Why does this matter?
You may find that you feel fine after using one sweetener, but another sweetener makes it harder for you to keep fasting.
Knowing what’s in the products you buy will make your detective work a little easier.
Stevia and the Gut Microbiome
Even though stevia may not affect our blood sugar, insulin, or fat burning directly to any significant degree, it does have indirect effects in our bodies.
That’s because stevia (and some other sweeteners) changes our intestinal bacteria (aka gut microbiome, or gut flora).
Research is still very limited, but there is increasing evidence that the makeup of our gut microbiome influences metabolism and various diseases, including diabetes, obesity, cancer, and even mental illness.
If you want to dive deeper, here’s a fascinating podcast episode about the gut microbiome.
How can you actually use this?
If you want to fully optimize your health, it’s probably better to stick with “whole foods” (when you’re not fasting), and avoid sweeteners and other processed foods as much as possible.
I’m not perfect about this either, but it’s a good concept to at least be aware of.
Sidenote: This is also a good reason to avoid taking antibiotics any time you don’t really need them (like almost every time you have a cold or sore throat, for example).
Stevia and Cancer
At very high concentrations in a test tube stevia is harmful to DNA, but it doesn’t have these effects at reasonable human doses.
Why does this matter?
While I don’t think stevia will significantly increase your risk of cancer, maybe you should avoid guzzling down Zevia soda by the gallon. 🙂
When it comes to artificial or other processed sweeteners, try not to use more than necessary.
If I Choose to Use Stevia, How Much Should I Take?
There’s no hard-and-fast rule, just don’t go completely crazy.
A few “servings” per day (as defined on the package) is probably a reasonable amount.
Is Stevia the best sweetener to use while fasting?
Overall, stevia seems like a pretty reasonable option when fasting.
The same thing may or may not be true of other sweeteners.
Do sucralose, aspartame, or maltodextrin “break” a fast?
More to come on these topics soon…after I do a bit more research.
For now, I’d say stevia is probably among the better choices when it comes to sugar substitutes to use while fasting. Allulose and monk fruit also seem like pretty good options.
Conclusion – What’s the Bottom Line?
I can’t emphasize this enough:
If stevia makes it easier for you to fast, it’s probably worth using it.
Fasting is still very beneficial even if you consume stevia.
(The same thing is true of most other supplements, such as apple cider vinegar or lemon water, for example.)
However, if you’re one of those people who gets hungrier when you consume stevia, you should definitely avoid it while fasting.
When it comes to supplements and fasting, no two people are alike, so you’ll need to experiment and see what works for you.
As you get more experienced with fasting, your body will adapt, and you’ll probably feel less and less need to use stevia or other sweeteners while you fast.