We are often asked, “Does coffee break intermittent fasting?” So we decided to put black coffee to the test!
To do this, we spent two different days testing our blood glucose and ketones. We bring you our results in this blog post!
Can I Drink Black Coffee – At-A-Glance
- Two tests were performed. One with no coffee over a two-hour period and one with black coffee over the same time period.
- Both Becky and Keith’s blood glucose levels went down after consuming black coffee.
- Becky’s ketone level increased after consuming black coffee. Keith’s ketones were not significantly influenced.
Can I Drink Black Coffee While Intermittent Fasting? [Video]
In this video, you’ll learn…
- How black coffee affected our blood glucose and ketones during a fast
- How black coffee compared to no coffee
- Our conclusion on whether or not coffee breaks a fast
Does Coffee Break Intermittent Fasting – Our Predictions
Coffee does not have any calories, so it does not break a caloric fast.
If you follow us, you know we have tested a lot of different things.
Some of those things were non-caloric sweeteners.
Despite having no caloric value, they did have some metabolic effect on us. It was either lowering our ketones or raising our blood glucose.
So it wasn’t a “slam dunk” that coffee, even though it didn’t have calories, wasn’t going to affect anything.
We were hoping it wouldn’t affect anything.
Oh my gosh, that would be upsetting.
Side note: We used half-caffeinated coffee for this experiment. In the sixteen ounces of coffee, we estimated a hundred milligrams of caffeine total.
The Scientific Method
Here is what we did:
- We tested over two days.
- We tested no coffee on the first day.
- We then tested sixteen ounces of black coffee on the second day.
- We took a baseline study on both of our test days.
- This means at zero minutes, we tested our blood glucose and ketones to see where we were starting that morning.
- We then test it again at 30 minutes, 60 minutes, and 120 minutes.
Two hours of fun!
Results: Becky’s Blood Glucose
Let’s start with my blood glucose with no coffee compared to my glucose with coffee.
So here is what we found:
So without coffee, you [Becky] started that 75 mg/dL that morning, went to 70 mg/dL at 30 minutes, stayed at 70 mg/dL at 60 minutes, and went up to 81 mg/dL after 120 minutes.
All in all, that is an eleven point swing, but that’s relatively insignificant.
It really is.
With coffee, you started at 74 mg/dL, went to 77 mg/dL at 30 minutes, went down to 66 mg/dL at 60 minutes, and back up to 74 mg/dL after 120 minutes.
So again, a little bit of movement in the readings.
However, when you take into account the possible error of testing itself, it is pretty insignificant.
So we didn’t do any exercise, we didn’t have any supplements, and we didn’t do anything else during or before out testing.
So, we didn’t control every variable, but there was not that much difference in my blood glucose.
Coffee did not seem to influence Becky’s blood glucose significantly
That’s also why testing dates are not very fun – you can’t do anything during these two hours!
I’m just throwing that out there.
Well now that that is thrown out, let’s take a look at what happened to your glucose when you drink no coffee, compared to when you drink coffee.
Results: Keith’s Blood Glucose
My no-coffee day started at 101 mg/dL, went to 100 mg/dL after 30 minutes, to 103 mg/dL after 60 minutes, and down to 99 mg/dL after 120 minutes.
I only had a four-point range.
So, really, it did absolutely nothing to my blood glucose.
Which, you would expect it not to do anything because it is nothing.
So when I had coffee, I started at 107 mg/dL, went to 111 mg/dL after 30 minutes, down to 92 mg/dL after 60 minutes, and further down to 78 mg/dL after 120 minutes.
So that’s a 29 point difference.
That is pretty significant!
You have probably seen it before.
I often start the mornings a little higher on the glucose readings and little lower in ketones.
However, for black coffee to drop my blood glucose like that, that’s pretty substantial.
Coffee resulted in a significant drop in Keith’s blood glucose compared to no coffee.
We have also talked about the “dawn effect” before.
This may explain having a high glucose reading in the morning, but yeah; That was interesting.
So if we can conclude anything from that, we can say that coffee did nothing to my [Becky] glucose, but for you, it may have given you a little bit of an edge.
Yeah, I get to have coffee, and you don’t.
No, I don’t think that’s what that means.
Results: Becky’s Ketones
Now let’s take a look at what the changes were in our ketones.
So my ketones with no coffee compared to my ketones with coffee.
Alright. With no coffee, you started at 1.8 mmol/L.
That is very good.
At 30 minutes it was 1.7 mmol/L, 1.9 mmol/L at 60 minutes, and 1.6 mmol/L at 120 minutes.
So, again, the readings stayed relatively stable during that whole time when you had no coffee.
You [Becky] started at 1.2 mmol/L, you jumped up to 1.6 mmol/L 30 minutes after drinking coffee, went to 1.6 mmol/L at 60 minutes, and 2.1 mmol/L at 120 minutes.
So a substantial increase again in ketones when you drank coffee.
Coffee resulted in a significant rise in Becky’s blood ketones compared to no coffee.
Also, that was black coffee; there was nothing mixed in it.
So there you go, I can have coffee too!
Okay, I guess we can both have coffee.
Results: Keith’s Ketones
Let’s take a look at what happened to your ketones when you did not drink coffee compared to drinking coffee.
So, as we just said, my ketones are low a lot of times.
I’m not in ketosis, technically, first thing in the morning.
[With no coffee] I started at 0.4 mmol/L, went to 0.3 mmol/L at 30 minutes, to 0.4 mmol/L at 60 minutes, went to 0.4 mmol/L at 90 minutes.
So I stayed pretty much the same that entire time on the morning that we had no coffee.
If you look at my ketones when we had coffee, I started at 0.3 mmol/L. Another stellar morning.
That dropped down to 0.2 mmol/L at 30 minutes, to 0.2 mmol/L at 60 minutes, and 0.2 mmol/L again at 120 minutes.
The readings just stayed pretty steady. It didn’t do anything to my ketones at all.
Coffee did not seem to influence Keith’s blood ketones significantly
However, again, I had a better glucose result, and you had a better ketone result.
Well, but both of those readings improved with coffee.
Conclusion: Does Coffee Break Intermittent Fasting
So here is the bottom-line:
Does coffee break intermittent fasting?
Well, we don’t see any reason why not!
If anything, there is a possibility that it might help you.
It lowered Keith’s blood glucose, and it raised my ketones.
CONCLUSION: Coffee did not seem to break our fast. Instead, it may have helped our ability to burn fat because it lowered Keith’s glucose and raised Becky’s Ketones.
So, there you go.
We’re going to keep drinking it!
We will keep drinking coffee while intermittent fasting.
With that said, you might want to do your own testing, but as far as we’re concerned coffees got the thumbs up!
Thanks so much for reading, please subscribe to our YouTube channel. We do a lot of these tests, and we’re happy to bring them to you.
What Breaks a Fast? Our Tests
- Will Cream, MCT Oil, or Butter Break My Fast?
- Will Keto (Bullet-Proof) Coffee Break Intermittent Fasting?
- Can I Have Cream in Coffee When Fasting?
- Will Ghee Break My Intermittent Fast?
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 from Palmer College of Chiropractic in Davenport, Iowa.