Coffee Experiment! What Can I Put In My Coffee When Intermittent Fasting – We Ran The Test

Coffee Experiment! What Can I Put In My Coffee When Intermittent Fasting – We Ran The Test

Are you worried that adding things to your coffee will break your intermittent fast?

Your worries are over!

We stuck our finger 16 times over a 4-day period to bring YOU a definitive answer about how your body handles black coffee, cream, MCT Oil, and butter.

Let’s figure out once and for all if these additions to your morning coffee will break your fast!

What Coffee Additive Breaks My Intermittent Fast? Cream, MCT Oil, or Butter [Video]

In this video we’ll answer…

  • Does black coffee break my fast?
  • Can I have cream in my coffee when I’m intermittent fasting?
  • Can I have MCT oil in my coffee and not break my fast?
  • Will butter in my coffee break my intermittent fast?

Here’s How We Tested Coffee and Intermittent Fasting

Doctor Keith and I are both science geeks at heart, so we decided to follow the scientific method.

coffee and intermittent fasting- scientific method comment

This means we started with a hypothesis, decided how to test that hypothesis, gathered our results, and came to our conclusions.

Day 1: Testing Black Coffee

Hypothesis

coffee and intermittent fasting-Hypothesis 1

Our first hypothesis was mostly a control to see what happened to our ketones and glucose levels when we drank 16 ounces of black coffee.

We hypothesized that if we drink 16 ounces of coffee while intermittent fasting, it will NOT knock us out of ketosis or spike our blood glucose.

Materials and Methods

The materials we used were:

  1. Precision Xtra ketone and glucose meter, which you can buy here.
  2. Ketone and glucose strips
  3. 16 ounces of black coffee

We followed a 16:8 Intermittent fasting schedule. This means we stopped eating by 8 pm the night before the tests and did not plan to start eating until 12 pm the day of the tests.

We performed the test over a period of two hours.

We started by taking an initial reading at 0 minutes.  We then tested again at 30, 60, and 120 minutes.

During that time, we did not exercise or consume any supplements.

To make sure we stayed consistent with how we drank coffee, we decided to drink 8 ounces of black coffee in the first 30 minutes, and the other 8 ounces in the next half hour.

Results

Becky’s ketone level results:

coffee and intermittent fasting- b ketone black coffee

As you can see from these results, Becky’s ketone level after drinking black coffee went up, showing that she was deeper into ketosis.

Keith’s ketone level results:

coffee and intermittent fasting-k ketones black coffee

Keith’s ketone levels went down by only 0.1 mmol/L.

Becky’s blood glucose results:

coffee and intermittent fasting-becky glucose black coffee

Becky’s glucose readings for black coffee started low and stayed low.

coffee and intermittent fasting-Keith glucose black coffee

Keith’s blood glucose results:

Keith’s glucose readings started somewhat high (which is normal for him) and then went down.

Day one of pricking our fingers was done, and our hypothesis was accepted!

Black Coffee Conclusion: Drinking Black Coffee while Intermittent Fasting will NOT break your fast or knock you out of ketosis.

Day 2: Testing Cream in Coffee

Hypothesis

coffee and intermittent fasting-Hypothesis 2

We hypothesized that if we drink 16 ounces of coffee with heavy cream while intermittent fasting, it will NOT knock us out of ketosis or spike our blood glucose.

Materials and Methods

We used the same materials and methods as before, only this time we added 2 tablespoons of heavy (whipping) cream to each of our 16 ounces of coffee.

Results

Becky’s ketone level results:

coffee and intermittent fasting- becky ketone heavy cream

As you can see from these results, Becky’s ketones started at 1.8 and rose to 2.1 mmol/L.

Keith’s ketone level results:

coffee and intermittent fasting-keith ketone heavy cream

Keith’s ketones started at .2 and went up to .3 mmol/L

Becky’s blood glucose results:

coffee and intermittent fasting-becky glucose heavy cream

Becky’s blood glucose dropped by 10 points over the 120 Minutes.

Keith’s blood glucose results:

coffee and intermittent fasting-keith glucose heavy cream

Keith’s blood glucose went up at first, but then settled down after 120 minutes to return to very near the initial level.

Day two of pricking our fingers was done, and our hypothesis was accepted!

Coffee with Cream Conclusion: Drinking Coffee with Heavy Cream while Intermittent Fasting will NOT break your fast or knock you out of ketosis.

Day 3: Testing MCT Oil in Coffee

Hypothesis

coffee and intermittent fasting-Hypothesis 3

We hypothesized that if we drink 16 ounces of coffee with MCT Oil while intermittent fasting, it will NOT knock us out of ketosis or spike our blood glucose.

Materials and Methods

We continued to follow the same methods as our previous days of testing, but on this day, we put 1 tablespoon of MCT oil in 16 ounces of coffee.

Results

The results were surprising!

Becky’s ketone level results:

coffee and intermittent fasting-becky ketone mct oil

Becky’s ketones rose from 2.3 to 3.2 mmol/L.

Keith’s ketone level results:

coffee and intermittent fasting-keith ketones mct oil

Keith’s ketones started at .5 and went up to .8 mmol/L. However, take notice that there was a peak of 1.3 mmol/L at 60 minutes.

Becky’s blood glucose results:

coffee and intermittent fasting-becky glucose mct oil

Becky’s glucose reading dropped by 9 points.

Keith’s blood glucose results:

coffee and intermittent fasting-keith glucose mct oil

Keith’s glucose reading dropped by 7 points

Day three of pricking our fingers was done, and our hypothesis was once again accepted!

MCT Oil was interesting! We both experienced a rise in ketones and drop in blood glucose readings after 120 minutes when we consumed MCT oil. That is the desired result!

Coffee with MCT Oil Conclusion: Drinking Coffee with MCT Oil while Intermittent Fasting will NOT break your fast or knock you out of ketosis. In fact, MCT Oil will increase ketones and lower blood glucose.

Click here to check out another experiment we did, where we tested whether or not MCT Oil as a supplement will accelerate fat loss.

Day 4: Testing Butter in Coffee

Hypothesis

coffee and intermittent fasting-Hypothesis 4

We hypothesized that if we drink 16 ounces of coffee with butter while intermittent fasting, it will NOT knock us out of ketosis or spike our glucose.

Materials and Methods

We used the same methods that we had been using all week, but this time we put 2 tablespoons of Kerry Gold butter in our 16-ounce coffees.

Results

Becky’s ketone level results:

coffee and intermittent fasting-becky ketones butter

After drinking coffee with butter, Becky’s ketones rose from 2.1 to 2.6 mmol/L.

Keith’s ketone level results:

coffee and intermittent fasting-keith ketones butter

Keith’s Ketones started at 0.5 and rose to 0.6 mmol/L.

Becky’s blood glucose level results:

coffee and intermittent fasting-becky glucose butter

Becky’s glucose level dropped by 6 points.

Keith’s blood glucose level results:

coffee and intermittent fasting-keith glucose butter

Keith’s Glucose level dropped by 13 points.

Day four of pricking our fingers was done, and our hypothesis was again accepted!

Coffee with Butter Conclusion: Drinking Coffee with Butter while Intermittent Fasting will NOT break your fast or knock you out of ketosis.

Discussion of Results Regarding Coffee and Intermittent Fasting

While this was a small study, our results show the following:

  1. None of the coffee additives caused a spike in our blood glucose levels. In fact, they were more likely to lower our blood glucose levels. After 120 minutes, our blood glucose levels dropped on all four days. In other words, drinking black coffee as well as coffee with cream, MCT oil, or butter lowered our blood glucose.
  2. None of the coffee additives caused a significant drop in our blood ketone levels. At 120 minutes, my, (Becky’s), ketone readings increased after drinking black coffee, coffee with cream, coffee with MCT oil, and coffee with butter. At 120 minutes, Keith’s ketone readings dropped by 0.1 mmol/L after drinking only black coffee. His ketone readings rose slightly after consuming coffee with cream, MCT oil, and butter.
  3. MCT oil caused an impressive rise in blood ketone levels and a drop in blood glucose for Becky and Keith.

Conclusion: Coffee and Intermittent Fasting

Since there was an overall drop in our blood glucose readings and no significant drop in ketone readings, we conclude that…

Adding Cream, MCT Oil, or Butter to coffee does NOT break your intermittent fast.

Since MCT Oil significantly increased our blood ketone readings, we can also conclude that…

If you are following a ketogenic diet, MCT Oil is beneficial to add to your coffee while intermittent fasting.


To learn how Dr. Keith lost 80 pounds and dramatically improved his health, >>check out our 21 day challenge<<.

What Breaks a Fast? Our Test

33 thoughts on “Coffee Experiment! What Can I Put In My Coffee When Intermittent Fasting – We Ran The Test

  1. This is excellent, thank you! One thing I would love to see added to this research is the keto effect of just water over those 120 minutes, and THEN the keto effect of adding a tad bit of protein, such as collagen powder (I use the green tub great lakes powder; it dissolves great in coffee). I feel like that might put your test even more into an annals of science, and for us folks who don’t have the finger prick blood testers, it would be fun to know. Also, sugar free sweeteners like splenda (!!) or stevia–do they have any effect? Anyway–great read, exactly what I was looking for when I googled my question.

    1. Hi Kari, on our 2FitDocs YouTube Channel, we have tested different sweeteners. Here is the video: http://bit.ly/2uYWdJJ

      We also have a video coming out soon on no coffee vs black coffee and plan on doing protein sources in the future, so when you arrive at the video, be sure to subscribe!

  2. So very interesting, I was captivated reading your results—thank you! I would also love to see added to this research the keto effect of just water over those 120 minutes, and then the keto effect of adding collagen powder to your coffee. So appreciative of all that wincing-sticking-your-fingers that you both endured to help give us clarity in what goes on with our ketones and glucose when drinking our coffees with different add-ins. Great read!

    1. Thanks for the suggestion, Nancy! We did a no-coffee day and that will be uploaded to YouTube soon, so you might want to subscribe to our YouTube Channel to catch it. You can subscribe on this page: https://www.youtube.com/2fitdocs

      We also plan on testing protein in the near future.

  3. Very interesting, and thanks.

    Wonder what your thoughts are regarding the drop in glucose levels following MCT and butter ingestion. Could it be due to insulin secretion in response to a fed state, and could this be evidence suggesting that MCT and butter ingestion do, in fact, break a fast?

    Just another interested, fit doc.

  4. Hello, I am confused by your result. I understood you to say that black coffee alone kicked Keith out of ketosis, but conclusion says no, not kicked out. Am I missing something here or did I mishear what you said of his ketone result? Thanks.

  5. I’ve read several places that adding gelatin or collagen to coffee breaks the fast, but I don’t understand why since there are no carbs, only protein, and fewer than 50 calories per tablespoon. Have you tested this? It would be great to be able to add protein to my morning coffee so I would love to know. Would also love to know if one tablespoon of coconut cream affects ketones and glucose.

    1. On a 16:8, i was drinking Bulletproof coffee with BP collagen in the mornings for months, with no results at all. I cut out the collagen, am only adding MCT Oil and I’ve dropped 8 lbs in 6 days. I asked Dave Asprey and he said that the collagen does kick you out.

  6. That’s a great read… one of a kind.
    I’m a big believer in the science approach…. show me proven results & method of testing any day.

    Thought for the future… MCT Oil ‘with’ Cream (in coffee).
    You could go on forever! haha

  7. Hello Becky & Keith – I am using coconut cream in my coffee during intermittent fasting. Will it break my fast? Is heavy cream and coconut cream the same? Would appreciate your reply. Thanks.

  8. I dont think this test presents the whole picture. Dairy products can spike insulin levels based on the protiens (not the carbs) in dairy products, without raising blood glucose. When intermittent fasting, part of the benefit is to take insulin out of the picture during the fast. You could be increasing yur insulin levels using dairy products but not see a change in blood glucose.

  9. Thanks for doing this experiment. I would have loved to see what happens when you add sugar. Also, can we assume that each person’s response will be different? Hence the need for “Personalized Nutrition” or a test like Nutrigenomix? Warm regards, Angela

  10. I would love to know if a creamer with 5g of sugar per serving will knock you out of ketosis? Specifically, I use Coffee-mate Natural Bliss Vanilla. But I also love Trader Joe’s Vanilla creamer. Thank you! And thank you both for doing the experiment. I found it very helpful!

      1. If it has carbs and those have 5g of sugars (carbs) it will knock you out. At that point its is not just cream anymore. Stevia is probably the only thing that is sweet that can be added, but do so sparingly it is that need for sweetness that is part of the problem. try to reset what your need is for sweetness.

  11. Dr. Becky,

    What about adding half and half instead of heavy cream? Would the milk (sugar) raise blood glucose as opposed to just the fat in the cream?

  12. Hi thanks so much for the information. There are SO MANY different opinions on this subject on the net and it’s always very confusing to figure it out.
    My question about this is, how many cups of coffee with 1-2 tablespoons of heavy cream would be allowed in a 20-24 hour fast? I’d really appreciate some info. Thank you and hope to hear from you soon.

  13. What about the calorie content of whatever you’re adding? Is there a calorie threshold to look out for to not break your fast?

  14. Wow thank you guys for all you gathered data and finger pricks! You totally brought some clarity with facts on a subject all us coffee drinkers have! Thank you

  15. There is much more to the equation than glucose and ketones regarding intermittent fasting isn’t there. Does autophagy get stopped in its tracks even if you technically don’t get kicked out of keto?

  16. I am considering adding intermittent fasting into my Keto lifestyle and have been somewhat puzzled by the do’s and don’ts about coffee – this is so helpful! It seems I could add 1 tablespoon of heavy cream into coffee x 2 cups and still be fine. What are your thoughts on whether adding 2 pumps of sugar free coffee syrups like Torano or Jordan’s would be ok or would definitely break the fast?

  17. Can you please share the amount of cream one can have in the coffee? I have never been able to do intermittent fasting due to my love of cream in my espresso. I do use quite a bit -maybe 1/3 cup heavy cream to 2/3 cup espresso! I know .,a ton of cream ! Thanks in advance for this info ! I have a Keto Mojo so I could also test my own ketones and glucose levels. What is acceptable to still be getting benefit of IF?

  18. What about just straight up half-and-half? You went to all this trouble to find these results, and didn’t do the most common thing 99% of people put in their coffee :) Maybe we’re to assume if heavy cream works, then half-and-half will as well, I don’t know. Oh well, guess it’s forever one of the grand mysteries of the universe.

  19. So I just have a slim bone to pick. Were the glucose levels taken after working out or right after drinking the coffee with the extra content? Because my understanding is, if you take your blood sugar and it pretty much stays steady that means there is no insulin around to bind to these glucose molecules and it will stay pretty much within the same level, but if it drops without working out or doing any type of physical activity to burn glucose then that means insulin was released and caused your BGL to drop. I was just wondering about this.

  20. I was wondering if you know anything about adding collagen to your coffee while IF? The one I use has 40 calories and 10g of protein. Thank you.

  21. Hi,

    There still seems to be a question as to whether heavy cream (1 tbsp has .5 g of protein and .4 g of carbohydrate) is enough to stop autophagy? Do your results shed light on this question?

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