Sweeteners in Coffee & Fasting Round 2! Erythritol, Monk Fruit, Xylitol, Allulose

sweeteners in coffee and fasting - feature picture

Sweeteners in Coffee & Fasting Round 2! Erythritol, Monk Fruit, Xylitol, Allulose

Jump to: Erythritol Conclusion | Monk Fruit Conclusion | Xylitol Conclusion | Allulose Conclusion | Final Results | More Coffee Tests

We are back doing more testing on sweeteners in coffee and their effect on fasting.

In this post, we tested erythritol, monk fruit, xylitol, and allulose in our coffee. We want to see how these sweeteners will affect our blood ketones and blood glucose, and determine if they will break an intermittent fast.

Here are the results!

Results At-A-Glance:

Is it ok to put the following sweeteners in your morning coffee when you are intermittent fasting:

  • Erythritol: Depends on Metabolism
  • Monk Fruit: No
  • Xylitol: No
  • Allulose: Inconclusive

Also view our results for Stevia, Splenda, Sweet-N-Low, and Equal

Sweeteners in Coffee & Fasting Round 2! Erythritol, Monk Fruit, Xylitol, Allulose [Video]

“Can I put sugar substitutes in my coffee without breaking my fast?” We get this question a lot, so we ran the tests! Over the past 4 days, we tested our blood glucose and ketones after drinking coffee mixed with erythritol, monk fruit, xylitol, and allulose.

Sweeteners In Coffee And Their Effect On Fasting Round 2

Keith:

So I’ve got a smile on my face, but I’m not really happy.

A couple of weeks ago we tested Stevia, Sweet’N’Low, Splenda and Equal. Those results were not very good.

So we wanted to see if some of the other sugar substitutes, the sweeteners that a lot of you guys asked about, would also have an effect on our blood ketones and blood glucose.

So here we go again!

Today, we are testing more sweeteners in our coffee and their effect on fasting.

Sweeteners in Coffee and Intermittent Fasting: Methods and Materials

Becky:

Here we go again.

So we followed the same scientific method, meaning we:

  1. Came up with our hypothesis
  2. Tested our hypothesis
  3. Gathered our results
  4. Came to our conclusions

These are basically the same methods we used before.

Keith: 

Yeah, including no exercise, we intermittent fast (16:8), and no supplements.

So, we always start every morning with a baseline of 0 minutes, and then we test again at 30 minutes, 60 minutes, and 120 minutes.

Sweeteners in coffee and intermittent fasting - methods

Sweeteners In Coffee And Intermittent Fasting: Erythritol

Erythritol: Hypothesis

Keith:

Hypothesis number one:

Coffee with erythritol will NOT knock us out of ketosis or raise our blood glucose.

Becky:

So we put one tablespoon of erythritol in our morning coffees. We did this because, as far as we could find out, the equivalent typically for erythritol to sugar was a one to one (1:1) ratio.

(we had earlier tested one tablespoon of sugar, so we need to keep it consistent to compare)

Here are the results that we got with the tablespoon of erythritol in our coffees.

Erythritol: Becky’s Results

Keith:

Becky’s ketones started at 1.7 mmol/L and ended up at 2.1 mmol/L.

She did go up a little bit to 1.8 mmol/L at 30 minutes, and then down to 1.6 mmol/L at 60 minutes, and then back up to 2.1 mmol/L at 120 minutes.

sweetener-in-coffee-and-fasting-Erythritol-B-Ketones

Your glucose started at 77 mg/dL, went up a little bit to 90 mg/dL at 30 minutes, down to 79 mg/dL at 60 minutes, and up again to 77 mg/dL at 120 minutes. 

sweetener-in-coffee-and-fasting-Erythritol-B-glucose

So you ended up with your ketones being 0.4 mmol higher than when you started.

Next, glucose was almost exactly the same.

Becky:

So actually, if you just look at those results alone, it kind of looks like erythritol did pretty well for me.

My ketones went up a little bit, and my glucose stayed the same.

Keith:

However, we have to compare that to just the coffee without the erythritol.

Becky:

Right, and when I had only black coffee, my glucose stayed the same. 

Graph showing coffee vs erythritol effect on glucose

My ketones actually took a bigger jump up. They went up 0.9 millimoles from the start of the test to the end [with coffee] (see graph below).

Keith:

She had a two times bigger increase in ketones with coffee only when compared to the erythritol. 

Graph showing coffee vs erythritol effect on ketones

Becky:

Right, so the question becomes did erythritol blunt my body’s ability to produce ketones? I don’t know, but that is the question that arises.

Erythritol: Keith’s Results

Keith:

Right so here we go with my results, which are always so good. [sarcasm]

So my ketones started at 0.4 mmol/L, went down to 0.3 mmol/L at 30 minutes, then I was at 0.3 mmol/L at 60 minutes, and I ended the test at 0.3 mmol/L at 120 minutes.

sweetener in coffee and fasting Erythritol male ketones

So, my glucose started at 91 mg/dL, and it just gradually went up to 105 mg/dL at 30 minutes, 100 mg/dL at 60 minutes, and settled at 102 mg/dL at 120 minutes.

sweetener in coffee and fasting Erythritol male glucose

So that is 11 points up for me.

My ketones went down a little bit, which is negligible, but again if we look at those results, and we compare it to my black coffee results my ketones were nearly the same.

Graph showing coffee vs erythritol effect on ketones male subject

My glucose dropped 29 points with black coffee over the two hours.

So with an 11 point increase, and a 29 point decrease. That is a 40 point difference in my glucose results between those two.

Graph showing coffee vs erythritol effect on glucose male subject

Erythritol: Conclusions

Becky:

Right, and now we are getting into the significant numbers. So did erythritol increase your glucose?

Well compared to black coffee, we’d have to say yes.

Keith:

This is typical.

My issue seems to be a lot of times with my glucose, and your issue seems to be, a lot of times, with your ketones.

Becky:

I think it is an interesting thing that we are finding from all of this testing that we are doing.

We are really demonstrating the difference between two very different metabolisms: insulin-resistant vs. insulin-sensitive, and how these different sweeteners affect you.

Unfortunately, that is what it comes down to with our conclusions.

So will erythritol in your morning coffee raise your glucose? 

Keith:

Possibly.

Becky:

Depending on your metabolism for me no, but for you yes.

Will erythritol drop your ketones?

Keith:

Possibly.

Becky:

Right, depending on your metabolism. For me, no, but for you it’s possible.

Is it okay to put ERYTHRITOL in your morning coffee when you are intermittent fasting? 

Keith: Again, depends upon your metabolism. I would not.

Becky: So, drinker beware.

Keith: We give it a sideways thumb.

Sweeteners In Coffee And Intermittent Fasting: Monk Fruit

Monk Fruit: Hypothesis

Becky:

Alright, on to day two of our testing.

Keith:

We tested monk fruit which is Luo Han Guo. Is that how you say that?

Becky:

That’s as good as I could do.

Keith:

A lot of people ask about this one too.

So we only used half a gram in 16 ounces of coffee, which is less than like an eighth of a teaspoon.

We did this because we were trying to match the sweetness of one tablespoon of sugar. It is sometimes difficult to find those figures.

so our hypothesis was that:

Coffee with monk fruit will NOT knock us out of ketosis, or spike our blood glucose.

So what did we find? 

Monk Fruit: Becky’s Results

Keith:

So our findings for Becky were, her ketones started at 1.2 mmol/L, it went up a little bit to 1.7 mmol/L at 30 minutes, 1.5 mmol/L at 60 minutes, and then she finished at 1.2 mmol/L again at 120 minutes.

She ended right on the mark where she started. 

sweetener in coffee and fasting Monk Fruit female ketones

Her blood glucose started at 96 mg/dL, and it was up and down just a few points from there. She ended up at 91 mg/dL at 120 minutes. So I would say that it is kind of a negligible difference from start to finish for you.

sweetener in coffee and fasting Monk Fruit female glucose

Becky:

Here again, it looks like monk fruit had no effect. However, my ketones stayed the same with monk fruit. When I had just black coffee my ketones went up 0.9 mmol. 

Graph showing coffee vs monk fruit effect on ketones female

So again, we came to the same conclusion. Did it blunt my ability to produce ketones?

Maybe.

Keith:

Yeah, compared to only black coffee, it is not very good.

Monk Fruit: Keith’s Results

Keith:

So on to my results.

I started at 0.4 mmol/L, I went down to 0.3 mmol/L at 30 minutes, then I stayed at 0.3 mmol/L at 60 minutes, and I finished at 0.3 mmol/L at 120 minutes. 

sweetener in coffee and fasting Monk Fruit male ketones

My blood glucose started at 100 mg/dL, went to 99 mg/dL at 30 minutes, went to 100 mg/dL at 60 minutes, and ended at 95 mg/dL at 120 minutes.

sweetener in coffee and fasting Monk Fruit male glucose

I mean, that’s a pretty negligible change shown here. Everything just stayed kind of even.

So again, that doesn’t sound too bad, but I did have a 29 point decrease with black coffee only. 

Graph showing coffee vs monk fruit effect on glucose male

This stuff seems to be keeping my glucose at one level, where normally with just black coffee it would drop. 

Becky:

We seem to be seeing some effect on our body, or our liver, or something else. We at least know something is going on.

Keith:

It’s not like it is doing nothing.

Monk Fruit: Conclusions

Becky:

Correct. So will monk fruit raise your glucose?

Keith:

No, I’d say our results are pretty negligible.

Becky:

Will monk fruit knock you out of ketosis? 

Keith:

It’s possible. My number went down a little bit, but I wasn’t “technically” in ketosis.

Becky:

Right.

Keith:

Your number stayed the same, where normally with black coffee your ketones would go up.

So, again, it depends on your metabolism.

Is it okay to put MONK FRUIT in your coffee when you are intermittent fasting? 

Keith: I would not.

Becky: I also would not. We give it a sideways thumb.

Sweeteners In Coffee And Intermittent Fasting: Xylitol

Xylitol: Hypothesis

Becky

Okay on to day three.

Keith:

All right, hypothesis number three for the sweetener xylitol.

Let’s get it out of the way because I know we will get a lot of people who say it:

Don’t feed this to your dogs. It’s really bad for them. 

Sweeteners in coffee and intermittent fasting - warning for xylitol and dogs

Becky:

Got it.

Keith:

Okay, so we used a tablespoon of xylitol because it seemed to be a one-to-one ratio (1:1) with sugar sweetness. In previous tests, we had used one tablespoon of sugar.

Our hypothesis is:

Coffee with xylitol will NOT knock us out of ketosis, or spike our blood glucose.

Becky:

Let me add that xylitol does have a glycemic index of 12.

That is a pretty low glycemic index, but it is higher than these other ones that came in around one on the glycemic index. So, that was kind of a factor in the back of my mind while doing this test.

Sweeteners in coffee and intermittent fasting - glycemic index

Xylitol: Becky’s Results

Keith:

So with xylitol you started your ketones on that day at 1.6 mmol/L, you went up a little bit at the 30-minute mark to 1.7 mmol/L, but then you drop down to 1.2 mmol/L, and you finished the test at 1.3 mmol/L.

That is pretty unusual for you.

sweetener in coffee and fasting Xylitol- female Ketones

Your glucose was another unusual finding. It started at 86 mg/dL, went up to 109 mg/dL at 30 minutes, went up to 112 mg/dL at 60 minutes, and then settled in at 106 mg/dL at 120 minutes.

That was really unusual. 

sweetener in coffee and fasting Xylitol- female Glucose

Becky:

Yeah, and unfortunately those paralleled my results from sugar.

Wherewith sugar, I started at 1.3 mmol/L for my ketones and I went down to 0.7 mmol/L after 120 minutes.

graph comparing the effect of xylitol and sugar on ketones female subject

Keith:

But your blood glucose was still higher at the end of two hours with sugar, than it was with xylitol.

graph comparing the effect of xylitol and sugar on glucose female subject

Becky:

 Yeah, that wasn’t a promising result.

So we went on to your tests.

Xylitol: Keith’s Results

Keith:

Yeah, this is a really good day for me.

I was so excited that I started at 0.8 mmol/L ketones, but then I knew I was gonna have to drink that stuff.

Becky:

We should have used your “I’m an Angry Old Man” coffee mug

Keith:

Yeah, I think it says, “I’m Not an Angry Old Man.”

2 Fit Doc's coffee mug

Becky:

That would not apply to today.

Keith:

Don’t get me started.

So, my ketones started at 0.8 mmol/L, and then it just – Boom – went down 0.4 mmol/L at 30 minutes, then to 0.2 mmol/L at 60 minutes, and then settled at 0.3 mmol/L at 120 minutes.

sweetener in coffee and fasting Xylitol- male Ketones

So it just knocked me to the floor as far as my ketone production goes.

My blood glucose started 98 mg/dL, it went up to 113 mg/dL at 30 minutes, then stayed at 110 mg/dL at 60 minutes and at 120 minutes.

sweetener in coffee and fasting Xylitol- male Glucose

So again, you know, another rise in glucose.

Becky:

Yeah, so compared to your results from coffee alone that was really a lot worse. compared to sugar for you…

Keith:

Xylitol: Comparison To Sugar

For our sugar test, I actually started pretty high in ketosis.

Even though it knocked me out at the 60-minute mark, I actually came back into ketosis a little bit at 120 minutes. So, my body did handle that a little bit.

graph comparing the effect coffee and xylitol have on ketones in a male

Becky:

It seemed like there is a possibility that your body handled sugar better than it handled xylitol.

Keith:

Possibly.

I ended up with a seven-point increase in my blood glucose from 0 minutes to 120 minutes with sugar.

graph comparing the effect coffee and xylitol have on glucose in a male

With xylitol, this was a twelve-points change from 0 minutes to 120 minutes.

I think that xylitol actually seems worse than sugar.

Becky:

It does point to that.

I mean, this was a small test with only two people, with two different metabolisms, but we can conclude that the results were not positive. 

Keith:

Right, and we should point out before we forget, that this is an N of two (n=2). Right?

Two very different people.

If you have questions on specific stuff that you want to use, you need to test, because we can’t test everything.

Just test and see what happens with yourself because it may be different than what we are getting.

Sweeteners in coffee and fasting - Can I Eat

Xylitol: Conclusions

Becky:

So let’s do our conclusions on xylitol.

will xylitol raise your glucose?

Yes. 

Keith:

Yes, it is possible.

Becky:

Will xylitol knock you out of ketosis?

Keith:

I’d say it is possible.

Becky:

I would say possible. depending on metabolism.

Is it okay to put XYLITOL in your morning coffee when you are intermittent fasting?

Keith: I’m going to say no.

Becky: I’m going to say no as well.

We are going to give that one a definite thumbs down. That might be one of our first ones, and sorry all you xylitol fans out there.

Sweeteners In Coffee And Intermittent Fasting: Allulose

Allulose: Hypothesis

Becky:

All right, on to day four. Day four was allulose. 

So we get a lot of questions about allulose. It seems to be the new wonder sweetener.

Keith:

It looks like a little bag of cocaine, by the way.

Becky:

It certainly does.

Keith:

Hopefully, we don’t get raided while we’re doing our video.

Becky:

Okay, so our hypothesis for allulose:

Coffee with allulose will NOT knock us out of ketosis, or spike our blood glucose.

What did we find?

Keith:

So we used a tablespoon of allulose because again, all we could find was that this would be equivalent to the sweetness of a tablespoon of sugar (1:1).

Allulose: Becky’s Results

Keith:

So you started at 1.1 mmol/L, which is a little bit higher than normal. It went to 1.3 mmol/L at 30 minutes, then 1.2 mmol/L at 60 minutes, and then back to 1.1 mmol/L at 120 minutes. 

sweetener in coffee and fasting Allulose - female Ketones

You were exactly the same two hours later than you were at the start. 

Next, your glucose started at 83 mg/dL, went up to 82 mg/dL at 30 minutes, down to 78 mg/dL at 60 minutes, and you ended at 84 mg/dL at 120 minutes.

sweetener in coffee and fasting Allulose - female Glucose

Again, you were almost exactly where you started. Do you get that kind of idea like “well? So it didn’t do anything?”

Right? 

Becky:

Right. No effect, but…

Keith:

But, if we compare it to just coffee without any of the sweeteners, your ketones went up [with black coffee].

graph comparing the effect coffee and allulose have on ketones in a female

Becky:

Right, with just black coffee my ketones went up.

Keith:

So again, these things are NOT just doing nothing.

They are affecting us.

Allulose: Keith’s Results

Keith:

So another stellar day for me when it came to ketones.

Actually today I started at 0.3 mmol/L, I went to 0.3 mmol/L at 30 minutes, at 60 minutes I went to 0.3 mmol/L, and – drum roll – at 120 minutes I went to 0.4 mmol/L.

So, a very good day [sarcasm]

sweetener in coffee and fasting Allulose - male Ketones

My glucose started at 107 mg/dL, dropped a little bit to 99 mg/dL at 30 minutes, 93 mg/dL at 60 minutes, and 95 mg/dL at 120 minutes.

So, it did go down a little bit.

sweetener in coffee and fasting Allulose - male Glucose

Allulose: Conclusions

Becky:

All right, so let’s do our conclusions. 

Will coffee with allulose raise your blood glucose? 

Keith:

I’m going to say no.

Becky:

Will allulose in your coffee knock you out of ketosis?

Keith:

According to our results, I’m going to say no.

So is it okay to put allulose in your morning coffee if you are intermittent fasting?

Becky: You know, we are gravitating toward no, but it might depend on your metabolism. Let’s go with inconclusive.

Keith: Yeah, inconclusive. Also, none of these tasted very good.

Becky:

No, it didn’t taste good.

Keith:

So we’re glad to be done with this one.

Becky:

We are.

Keith:

We’re never going to revisit sweeteners in coffee and their effect of fasting again. I just want to put that out there.

Becky:

Alright, you ready? Let’s bring it home.

Sweeteners In Coffee And Intermittent Fasting: Final Results

So what did we find when we tested erythritol, xylitol, monk fruit, and allulose?

Were any of these better than black coffee alone? 

Keith:

None of them were better than black coffee alone.

sweeteners in coffee and fasting - results

Becky:

Sometimes they would raise your glucose, and sometimes they would blunt my ketones.

It was all over the place, but obviously, they are all doing something to your metabolism.

In our opinion, all of the sweeteners we tested are interfering with your body’s ability to naturally lower your glucose as you fast and increase your ketones.

Keith:

Right. So if you are intermittent fasting, and you are doing your keto coffee with some of the fats that we talked about in our other test, I would not add any sweeteners.

I think that they are going to, if not only blunt everything, they could actually be harmful too. 

If your glucose is going up, and you get some kind of insulin response at the same time you are putting fat in your body, it might not be a good thing.

Becky:

Yep, alright there you go.

Getting away from sweeteners is also getting yourself away from sugar cravings. It all works together.

We have actually mentioned this effect in some other videos.

So there you go.

Four more days of testing some sweeteners. I hope this was helpful, and that our results didn’t disappoint you.

I hope this experiment gets you farther on your path to good health. 


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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