Sweeteners in Coffee & Intermittent Fasting? We Ran the Tests!

sweetener break an intermittent fast- Feature Picture (1)

Sweeteners in Coffee & Intermittent Fasting? We Ran the Tests!

Video | Why Test | Methods & Materials | Stevia | Sweet’N’Low | Equal | Splenda

Sweeteners in coffee and their effect on intermittent fasting. Is it good or bad?

In this post, we test our blood glucose and ketone levels to find out if adding non-caloric sweeteners, like stevia, Sweet’N’Low, Equal, and Splenda to your morning coffee will break an intermittent fast?

Spoiler Alert: If you are a fan of artificial sweeteners, you may not be happy with some of our results.

Sweeteners In Coffee At Home Test Summary

  • Stevia did not raise our blood sugar, but it knocked Keith out of ketosis.
  • Sweet’N’Low raised our blood sugar, but it did not knock us out of ketosis.
  • Equal had a similar response to sugar – It raised keith’s blood sugar levels and knocked us both our of ketosis.
  • Splenda did not cause a spike in blood sugar, but it had a lowering effect on our ketones.

Sweeteners in Coffee & Intermittent Fasting…We Ran The Tests! [Video]

We spent 4 days testing our blood glucose and ketones to determine if non-calorie sweeteners would break our intermittent fast. Here are the results!
They may surprise you…

Why Are We Testing Sweeteners in Coffee?


A month or so ago we tested adding fats to our coffee as well as a few different things.

That seemed to be good with everybody and it answered a lot of questions, except for one question we kept receiving.

[The question] we got from, it seemed like every other person, was:

“Are sweeteners in my coffee going to affect my ketones, my glucose, and my intermittent fasting.”

sweetener in coffee and intermittent fasting-comments


Right. So, we are in round three of our testing, and we followed the same scientific method that we did when testing the fats.

Testing Sweeteners In Coffee and Intermittent Fasting: Methods & Materials

Our method was to:

  1. Come up with our hypotheses
  2. Test our hypotheses
  3. Analyze our results
  4. Come to our conclusions

The materials we used were a precision Xtra blood ketone and glucose monitor.

precision-xtra-monitor for blood glucose and ketones


So, we got up bright and early in the morning, pricked our fingers to test our baseline blood glucose and ketones, then put a sweetener into our coffee and drank that down.

We tested our blood at 30 minutes, 60 minutes, and 120 minutes.


Right, and we are also doing a 16-8 intermittent fast with no exercise and no supplementation.

That is what we normally do.

Spoiler Alert!

So here is the bad news: For all of you people who use sweeteners, you might not be happy with us after these videos.

Testing Sweeteners In Coffee and Intermittent Fasting: #1 Stevia

sweeteners-in-coffee-Stevia and intermittent fasting


Alright. So on to our first hypothesis:


If we put STEVIA in our coffee, it will not knock us out of ketosis or spike our blood glucose.


Also, this is pure stevia. It is not mixed with anything else.

Right, so we put 3/8 of a teaspoon in our coffee because on the package that is what it says is the equivalent of one tablespoon of sugar, which we tested in an earlier video.

Okay, and here are our results:

Becky’s Ketone Results: Stevia

Becky’s ketones were virtually unchanged.

She began at 1.2 mmol/L, went up a little bit to 1.4 mmol/L at the 30 minutes, stayed there at the 60 minutes, and then back to 1.2 mmol/L at 120 minutes.


Becky’s Glucose Results: Stevia

Her glucose was about the same.

She started at 84 mg/dL, went to 89 mg/dL at 30 minutes, and back to 82 mg/dL at 60 minutes, and finally 85 mg/dL at 120 minutes.


So she stayed almost exactly the same from the zero minute mark to the 120-minute mark.


Right, so you would think that stevia did not have any effect on me, and that would be one interpretation until you compare it to my black coffee results.

We had earlier tested my glucose and ketones with just black coffee alone with nothing mixed into it

When we did that, my glucose pretty much remained the same. It started at 74 mg/dL and ended at 74 mg/dL.


However, my ketones with just black coffee went from 1.2 mmol/L up to 2.1 mmol/L.



Right. So that means that the stevia kept your ketones from going up?


Yeah that is a possibility, right?

It may have blunted my ability to produce ketones, but who knows. It’s one person’s results.

Let’s look at what your results showed for stevia.

Keith’s Ketone Results: Stevia


So for stevia, my ketones started at 0.6 mmol/L, which I was really happy about!

I’m rarely in ketosis first thing in the morning (which may be related to the Dawn Effect)

At 30 minutes I was at 0.3 mmol/L, then I went to 0.4 mmol/L at 60 minutes, and then I went back to 0.3 mmol/L at 120 minutes.


So, it just slammed the door shut on me.

Keith’s Glucose Results: Stevia

My glucose started at 94 mg/dL, it went up a little bit to 99 mg/dL at 30 minutes, it went down a little bit to 89 mg/dL at 60 minutes, and then at the 120 mark I was at 93 mg/dL.


Almost the same glucose as I started with.

Again, I did not seem to have a big glucose change with this, but it did drop me out of ketosis.

Overall, the results of our stevia test were not major numbers. They were kind of major for me, but not major in the long run.

However, if we compare that to my findings with just black coffee, the black coffee did not do anything to my ketones.


So, that is kind of a thing, but it is especially interesting when you look at black coffee’s effect on my glucose.

My blood glucose dropped 29 points with only black coffee and nothing else over a two-hour period.


So again, if you just look at this data, it does not seem to have done too much, right?


However, when we compare our results from black coffee with stevia to our results from black coffee by itself, I had a better ketone response with black coffee alone.

You [Keith] had a better glucose response from coffee alone.

Will Stevia Break A Fast?


So our conclusions:

Will stevia raise our blood glucose?


Will stevia knock us out of ketosis?

for me no, but for you [Keith] yes.

So this one is going to depend on metabolisms.

We have two very different metabolisms right here.


Another inconclusive result, but compared to black coffee, I would not want to put it in my coffee.

I did not like the taste either.


Yeah, it was yucky.


So can you use Stevia during intermittent fasting? This is inconclusive. It is going to probably depend on your metabolism, and there is a possibility it could be screwing with your metabolism.


If you are taking in fat at the same time (i.e Keto Coffee) that you have some liver metabolism going on, it may be messing with your insulin response or glucose production and you could be backfiring a bit.


Okay. Next.

Testing Sweeteners In Coffee and Intermittent Fasting: #2 Sweet’N’Low



Hypothesis number two:


Coffee with Sweet’N’Low will not knock us out of ketosis or raise our blood glucose.


All right, so we are doing the pink packet now. This is Sweet’N’Low.

Sweet’N’Low’s first ingredient, interestingly enough, is dextrose.

Dextrose is one of those hidden names for sugar.

alternative names for sugar

Next on the ingredient list, we have saccharin, which is the artificial sweetener. Saccharin has kind of a checkered past.

Is Saccharin Safe To Consume?

Tab soda was the first thing that I remember it from. That was a real early American diet soda, and it had a terrible after taste. Then it kind of got on the bad list, and now it is kind of back on the good list.


It was unfairly labeled because the studies they did were on grossly overdosed rats, and they found out it did not translate to humans later on.

So I think it is thought of as basically safe at this point.


Still definitely not health food.

So we put a packet and a half of Sweet’N’Low in our coffee because, according to their official website, it is the equivalent of a tablespoon of sugar.

What were our results?

Becky’s Ketone Results: Sweet’N’Low


Your ketones started at 1.1 mmol/L that day. You actually went up a little bit over the 120 minutes.

You went up to 1.4 mmol/L at 30 minutes, it dropped a little bit to 1.2 mmol/L at 60 minutes, and then at 120 minutes, it was at 1.6 mmol/L.


So, that was a pretty good result.

Becky’s Glucose Results: Sweet’N’Low

Your blood glucose started at 70 mg/dL, went up to 81 mg/dL at 30 minutes, went down to 74 mg/dL at 60 minutes, and then at 120 minutes it was 73 mg/dL.


From start to finish, you had only a little bit of a rise in your ketones, and blood glucose stayed about the same.


Right, but with black coffee, my ketones went up 0.9 mmol/L. Here I went up to 0.5 mmol/L. It is not a huge amount.


If that was me, these numbers would be huge, but these are my numbers:

Keith’s Ketone Results: Sweet’N’Low

So I started at 0.3 mmol/L, stayed at 0.3 mmol/L at 30 minutes, and then went down to 0.2 mmol/L at 60 minutes, and ended at 0.2 mmol/L at 120 minutes.


You know, I was happy.

Keith’s Glucose Results: Sweet’N’Low


My glucose started at 107 mg/dL, which is interesting.

It seems like my starting glucose has gone up from the day before (The Stevia Test).

My glucose went to 117 mg/dL at 30 minutes, it went down to 103 mg/dL at 60 minutes, and then back to 118 mg/dL at 120 minutes.


That’s awfully high.

Will Sweet’N’Low Break A Fast?


So with Sweet’N’Low, Keith’s glucose actually went up 11 points, but with black coffee, your glucose went down 29 points.


That is a pretty significant difference.


Yeah, and I am at 118 mg/dL after the test. I think that looks like the perfect beginning of an insulin response.

I mean that is getting up there.


All right.

Will Sweet’N’Low in your morning coffee spike your blood glucose?


Well, it is possible.


It will depend on the metabolism again.


It has dextrose in it too.


It does, which is basically sugar.

Will Sweet’N’Low knock us out of ketosis?


I would say no to that one.


Yeah, I actually went up a little bit, and you went down just a hair, which is not significant.


So what are our results as far as putting it in your morning coffee when you are intermittent fasting? Is sweet’n’Low a good idea?

Keith: Inconclusive again. It is kind of a sideways thumb.

Becky: So, if it is giving Keith a bump in his blood glucose, then you do not want to be doing that and mixing it with fats like keto coffee. It’s not a good idea.


Also, it tastes yucky.

Testing Sweeteners In Coffee and Intermittent Fasting: #3 Equal

sweeteners-in-coffee-equal-1 Will it break a fast

On to day three! Hypothesis number three is:


Equal in our coffees will not spike our blood glucose or drop us out of ketosis.


So here again, Equal actually has ‘dextrose with Maltodextrin‘ in the ingredient list.

I’m not sure why they worded it that way.

Then aspartame is third on the ingredient list.

So [as we said before] dextrose is a hidden name for sugar.

Maltodextrin on the glycemic index is…


really high.

the sources for where maltodextrin lands on the glycemic index are anywhere from 85 to 105. One of the sources even said 106 to 236.



Right. whereas table sugar has a glycemic index of 65.

The glycemic index is a measure of how it is affecting your blood glucose.


Keep in mind, straight glucose is 100. That is the mark.


So, this is worse than just glucose, and then they also put aspartame in it.

Is Aspartame Safe To Consume?

Aspartame has some sketchy backstory as well.

It is actually an excitotoxin. This means it would cause the nerve cells of your brain to get excited to the point it can cause the death of nerve cells.


We see aspartame in diet sodas, kool-aid, and other stuff like that.

So we did not have high hopes, but we put a packet and a half in each of our coffees as that is the equivalent for a tablespoon of sugar, and here are our results.

Becky’s Ketone Results: Equal


So Becky started with a ketone level of 1.7 mmol/L, and it actually went up to 2.2 mmol/L at 30 minutes.

That was pretty interesting.

It came back down to 1.7 mmol/L at 60 minutes, and at 120 minutes it was at 1.4 mmol/L.


Her ketone results were a little bit lower.

Becky’s Glucose Results: Equal

Her blood glucose was at 94 mg/dL, it went up to 105 mg/dL at 30 minutes, then back to 94 mg/dL at 60 minutes, and up to 103 mg/dL at 120 minutes.


It kind of went back and forth a couple of times over the test in both your ketones and glucose.


When we look at my results for Equal, they are actually very similar to my results for sugar.



Yes. Your blood glucose definitely went up a little bit, and your ketones came down a little bit.


Nothing significant happened, I didn’t really benefit from it.

As far as your ketones go:

Keith’s Ketone Results: Equal


So for my ketones, I actually started at 0.8 mmol/L that morning.

I was super excited, and then I realized that I had to drink coffee with dextrose, maltodextrin, and aspartame in it.


At 30 minutes I dropped to 0.5 mmol/L, then I dropped to 0.4 mmol/L at 60 minutes. So I was technically out of ketosis at that point.

Then 120 minutes I popped back up to 0.6 mmol/L.


So, that was kind of interesting.

Keith’s Glucose Results: Equal

My glucose started at 101 mg/dL, went up to 114 mg/dL at 30 minutes, went back to 98 mg/dL at 60 minutes, and back up to 108 mg/dL at 120 minutes.


Again we see that result kind of bobbing around a little bit.

I think my Equal results were similar to the results of regular sugar.


I was in ketosis when we did the sugar test, I dropped out of ketosis and then bounced back in at the two-hour mark.

Will Equal Break A Fast?


So equal kind of gave us a similar response to sugar.

Will Equal spike our insulin levels?


with our blood glucose levels – it’s possible.


Right. We were both on the way up.

Will Equal knock us out of ketosis?


It did for me.


It did for a short time, and I don’t know if we can say that our results are statistically important, but it didn’t do us any good.



So can we put Equal in our coffee in the morning while intermittent fasting?

Keith: Inconclusive.

Becky: Yeah, I don’t think you are doing yourself any justice.


With the dextrose and maltodextrin, that is probably why we got similar to sugar.


Yeah, we were basically putting sugar in our coffee.


I don’t know how much aspartame is actually in there too, but I do know it tasted yucky.

Testing Sweeteners In Coffee and Intermittent Fasting: #4 Splenda


So on to day four. Hypothesis number four is:


Splenda in our morning coffee will not knock us out of ketosis or raise our blood glucose.


All right the Splenda ingredients are dextrose, maltodextrin, and sucralose.

In other words, sugar, sugar, and sugar.

Sucralose is derived from sucrose, which is table sugar, and it is like 600 times sweeter than table sugar.

So, they can call it a non-caloric sweetener because it is so sweet.

That is also why they have to put the fillers in like dextrose and maltodextrin.

Is Splenda Safe To Consume?

Splenda is not health food, and we are not fans. We are trying not to be biased, but we are not fans of it.

It has been implicated in some things.

For example, if you have hypothyroidism, I have seen studies that it will block the absorption of zinc. So. it might not be the best thing if you have thyroid issues.

So we put a packet and a half in our morning coffees because that is the equivalent of one tablespoon of sugar.

Here are the results:

Becky’s Ketone Results: Splenda


So your ketones on day four started at 1.5 mmol/L, dropped a little bit to 1.4 mmol/L at 30 minutes, then dropped a little bit more to 1.2 mmol/L at 60 minutes, and at 120 minutes it was at 1.2 mmol/L.


So definitely a little bit of lowering your ketones.

Becky’s Glucose Results: Splenda

Your glucose started at 94 mg/dL, went to 93 mg/dL at 30 minutes, went to 92 mg/dL at 60 minutes, and went to 91 mg/dL at 120 minutes.


So a negligible effect on glucose.

Keith’s Ketone Results: Splenda

I started at 0.3 mmol/L again, stayed at 0.3 mmol/L at 30 minutes, went down to 0.2 mmol/L at 60 minutes, and then went back up 0.3 mmol/L.


So another happy day for me…

Keith’s Glucose Results: Splenda

My glucose started at 116 mg/dL, which is pretty high.

It went up to 119 mg/dL at 30 minutes, it went down to 111 mg/dL at 60 minutes, and then back up to 115 mg/dL at 120 minutes.


That is a pretty high glucose result.

Will Splenda Break A Fast?


So let’s look at these results compared to our black coffee results.

If you look at mine independently, you would say, “Wow that didn’t do too much to me,” but if you compare that to my black coffee results:


Black coffee boosted my ketones by 0.9 points, and Splenda dropped my ketones by 0.3 points.

So not favorable for me for ketones.

Whereas you [Keith], interestingly enough, your black coffee results showed your blood glucose dropped like 29 points.



So, the glucose result was totally different.

The glucose should be dropping through those two hours if I’m not getting any food in, right?


Right. However, when you took in Splenda, it kept your glucose where it was.

So will Splenda in your coffee cause a rise in your blood sugar?


I would say no based on our results.


Yeah, compared to black coffee it is iffy.

Will Splenda drop us out of ketosis?


Possibly. It had a lowering effect.


That is a good way to put it, it had a lowering effect.


Based on our results, do we recommend putting Splenda in your morning coffee when you are intermittent fasting?

Keith: It is inconclusive. When we compare it to black coffee, it obviously had an effect on our ketones and blood glucose.

Becky: Yeah, and our personal conclusion on Splenda?


It tastes yucky.

In Conclusion: Are Sweeteners In Coffee Okay When Intermittent Fasting?


So let’s bring it on home!


We do not believe that any of these are good to be adding to your morning coffee, especially not to a keto coffee with added fats.

Also, they are messing with your metabolism.



Yeah, it really seems like either they are lowering our ketones or raising our blood glucose and you don’t want either of those to be going on during your intermittent.

So, sorry…



Also, they taste yucky.


So there you have it!

We have some other sweeteners on our to-do list, so we will be bringing you some more sweetener tests in the future.

For now, when it comes to the packets or stevia and other sugar substitutes, we recommend keeping them out of your coffee.

What Breaks a Fast? Our Other Tests

About the Authors

Dr. Becky Gillaspy DC, graduated Summa Cum Laude with research honors from Palmer College of Chiropractic in 1991.

Dr. Keith Gillaspy, DC, CFMP grew up in central Nebraska and earned his Doctor of Chiropractic in 1991.

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