Does Sucralose Break a Fast? [The Full Story, Backed by Science]

Does sucralose break a fast?

Sucralose (brand name Splenda) is the most popular artificial sweetener in the United States.

Sucralose / Splenda says it has zero calories, so it makes sense you’d want to use it while fasting. 

But does sucralose break a fast?

After researching this topic, here’s my take:

You may do okay fasting with sucralose in the short-term, but in the long run it will be harder to reach your fasting goals.

For the whole story, read on.

Splenda Nutrition: What’s in Sucralose?  

Sucralose is most often sold in small powder packets, which claim to have zero calories.

But there’s a catch. 

While sucralose itself has no calories, it’s typically mixed with dextrose (another name for glucose, a type of sugar) and maltodextrin (a carbohydrate).

contents of a Splenda packet

Splenda packets actually contain about 2-4 calories (foods with fewer than 5 calories per serving are allowed to list their calories as “zero” in the US).  

So, when you dump a Splenda packet into your coffee or tea, you’re not only getting sucralose (which has some questionable health effects on its own–see below), you’re also getting some extra sugar and other carbs. 

So that’s what is “in” sucralose–or at least in the powder packets. 

Now, how will sucralose affect you while fasting?

Will Sucralose / Splenda Break a Fast?

First, consider why you’re fasting.

Some common reasons to fast include:

  • Reduced body fat
  • Lower blood sugar 
  • Lower insulin
  • Increased ketone levels
  • Hunger control

Here’s how I look at it:

If something stops you from reaching your fasting goals, then it “breaks” your fast.

Let’s look at these common fasting goals in more detail, and how each one would be affected by sucralose.

Sucralose and Intermittent Fasting / Extended Fasting to Lose Body Fat

When you fast, no food energy is coming in so you start burning body fat for energy. That’s why fasting is a great way to burn fat.

Will sucralose interfere with fat loss when you’re fasting?

It’s hard to say for sure–I don’t think that exact question has ever been researched.  

On the other hand, there is some evidence that sucralose leads to weight gain and other metabolic issues over time.

This may be because people tend to feel less satisfied after consuming artificial sweeteners, and may end up eating more in the long run as a result.

Bottom line?

It might work okay in the short-term, but I wouldn’t recommend using sucralose while you fast if your main goal is to reduce body fat. 

Does Sucralose / Splenda Raise blood sugar while fasting?

Blood sugar (glucose) tends to go down when you fast because you’re not consuming any sugar or other carbs.

That’s why fasting is particularly beneficial for people with diabetes (or prediabetes), whose blood sugar levels tend to be excessively high.

fasting lowers blood sugar graph timeline

Will sucralose raise your blood sugar while fasting?

Again, I don’t believe this exact question has been researched, but there is some related info we can look at.

In a 2017 study, healthy volunteers took sucralose over a period of several weeks, and their blood sugar didn’t get significantly higher.

But that’s not the whole story.  

A 2014 study (in rats) showed sucralose and other artificial sweeteners alter gut bacteria, leading (indirectly) to glucose “intolerance” (which means their bodies couldn’t clear sugar from the bloodstream as efficiently). 

Also, don’t forget that Splenda packets actually contain sugar

It’s probably not a good idea to eat sugar when you’re fasting if your main goal is to lower blood sugar. 🙂 

Bottom line?

If you’re fasting to lower blood sugar, I don’t recommend using Splenda / sucralose. 

Does Sucralose 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 the energy stored in your body can be released).

People with (type 2) diabetes or prediabetes tend to have abnormally high insulin levels, and fasting helps bring their insulin down to normal. 

I don’t think there’s any research about the effects of sucralose on insulin while fasting.

The 2017 study cited above and this 2009 study both suggest sucralose does not directly affect insulin levels.

However, multiple recent human studies (here, here, and here) suggest that sucralose makes you less sensitive to insulin with consistent use.

What does this mean?

If you become resistant to insulin, that means it doesn’t work as well in your body, and your body has to make more of it to try to get the job done.

It also means your blood sugar will go up over time, because insulin is struggling to move sugar into your cells (and out of the bloodstream).

Bottom line?

I would not recommend using sucralose if you’re fasting to lower insulin (or blood sugar) levels, as it will most likely backfire in the long run

Does Sucralose Break Ketosis While Fasting? 

Ketones are an energy source that your body makes from fat when you’re not eating carbs–kind of a replacement for sugar.

When you fast, you’re obviously not (or shouldn’t be) eating a lot of carbs, so your ketone levels go up.

The best part?

Fasting raises your ketone levels a lot more than just eating a ketogenic (low-carb, high fat) diet.

graph of fasting ketone levels timeline

As far as I know, there’s not any research about sucralose affecting ketone levels.

My personal experience suggests it doesn’t have much of an effect (at least not in the short-term).

For example, on various occasions I’ve consumed sucralose-sweetened products while fasting, and they didn’t seem to have much effect on my ketone levels.

Bottom line?

Sucralose appears to be okay while fasting if your main goal is to boost ketone levels.

Sucralose, and Fasting to Control Hunger 

This may be the most important question of all: 

Will sucralose make it harder for you to fast?

In general, fasting helps control hunger (maybe not on day one, but gradually over time).  

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. 

fasting reduces hunger over time, timeline graph

But there’s a catch.  

Some people feel hungrier when they use sucralose (or other artificial sweeteners), so it’s harder for them to keep fasting. 

This is supported by clinical experience as well as research.

For example, in a recent study artificial sweeteners seemed to increase cravings for sweets.  

That’s not something you want when you’re fasting.  

My personal experience has led me to similar conclusions.

For example, a couple months ago I drank multiple cans of diet soda each day during a 4-day fast (I was trying to use it all up before quitting artificial sweeteners…sometimes I’m a little crazy like that).

While I still got through the fast, I definitely noticed a difference–I felt hungrier than usual, and my energy levels seemed lower compared to a typical extended fast.

(I realize most diet soda is made with aspartame, but some has sucralose, and I’ve had similar experiences with sucralose-sweetened products in the past as well.)

Bottom line? 

Sucralose may make you feel hungrier while fasting, so be cautious, and try to avoid it if you can.

What Else Should I Know About Sucralose?

Let’s run through a few other common issues or questions that come up. 

Is sucralose the best sweetener to use while fasting?

Probably not.

It appears to have a variety of harmful effects, and may make it harder for you to fast.

I also wouldn’t recommend aspartame (the most common artificial sweetener in diet soda, energy drinks, and chewing gum), because it appears to be similarly harmful to health.

My top pick with what I know right now would probably be stevia

Monk fruit is another “natural” sweetener that seems fairly healthy as well, but I need to do more research before I decide for sure.

More to come on this, as well as some of the other sugar substitutes (like erythritol), after a little more investigation. 

Other Names for Sucralose 

Splenda is by far the best known product name with sucralose.

One other is Canderel Yellow (original Canderel is made from aspartame and does not contain sucralose).

I’m sure there are some other combo products out there with sucralose, so keep an eye on the actual ingredients in any sweeteners you buy. 

Sucralose and the Gut Microbiome 

In addition to any direct effects on health, sucralose may also have indirect effects on our health by changing the bacteria in our intestines (aka the gut microbiome, or intestinal flora).

This has been shown in animal studies, including the rat study cited above, and others.

It may also be why sucralose appears to cause insulin resistance and long-term weight gain, as mentioned above.

While these effects haven’t been thoroughly studied in humans, they’re definitely a cause for concern. 

There is increasing evidence that the makeup of our intestinal bacteria influences metabolism and many diseases, including diabetes, obesity, cancer, and even mental illness.  

(If you want to learn more about the gut microbiome, here’s a fascinating podcast episode you can check out.) 

How can you actually use this?

Basically, don’t jack up your microbiome. 🙂

Do your best to avoid substances that can be harmful to your intestinal bacteria, such as artificial sweeteners…or a more obvious example, antibiotics.

I’m not perfect about this either, but it’s a good concept to at least be aware of.

Artificial sweeteners and breastfeeding

On a recent podcast episode I learned that artificial sweeteners also get into breast milk.

And that’s not all.  

Kids are significantly more likely to become obese if their moms consume artificial sweeteners while pregnant or breastfeeding.  


By the way, the podcast guest was Michael Goran, PhD, an expert in childhood obesity and diabetes. 

He’s also the author of a new book called Sugarproof , which looks like a great resource for anyone who doesn’t want their kids to get addicted to sugar or other sweeteners (hopefully that’s everyone). 🙂

Cooking with Sucralose 

Sucralose is a bit more heat stable than other artificial sweeteners, so some people like to use it in baking or other cooking.

However, some newer research suggests heating sucralose above about 246℉ produces toxic chemicals.  

As a result, I would not recommend cooking with sucralose (or any artificial sweeteners, really).

Splenda Side Effects

If you’re a fan of bulleted lists, check out this one that summarizes the Splenda / sucralose side effects we have evidence for:

  • Long-term weight gain
  • Glucose intolerance
  • Insulin resistance
  • Increased hunger
  • Harmful to gut bacteria 
  • Toxic compounds when heated 

Sounds like a recipe for…not great things.

Conclusion – What’s the bottom line?

fasting with sucralose or Splenda summary chart

I can’t emphasize this enough:

You may be able to get away with consuming sucralose while you fast, but it’s probably not good for your health, and you’ll be less likely to achieve your fasting goals in the long run.

Not only does Splenda appear to cause insulin resistance and long-term weight gain, it’s probably also bad for your gut bacteria (which can cause a lot of indirect health effects).

It also makes some people hungrier, which means it will be harder to fast.

And don’t forget, sucralose / Splenda packets typically contain sugar (dextrose) and other carbs (maltodextrin).

So while you can have artificial sweeteners while you fast, I don’t think it’s a good idea.

What should you use instead?

If you want a sweetener, stevia may be a better option (as mentioned above).

For other fasting supplements, there are plenty you can choose from.  

For example, apple cider vinegar and lemon water are typically okay in moderation, and boullion is a great way to keep your salt levels up.

So does Splenda break a fast?

Maybe, maybe not. But either way, it’s not good for you.

And don’t forget – the more you fast, the more your body will adapt, and eventually you may not crave sweeteners at all. 

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Hope it helps!

Ben Tanner, PA-C

Ben Tanner, PA-C

Ben has been practicing as a physician assistant (PA, or PA-C, similar to a doctor) in emergency medicine, urgent care, and family practice since 2014. Since 2016, he has developed an avid interest in various forms of fasting, using it to improve his own health while helping friends, family, and patients do the same.