One of the most common questions I get about intermittent fasting is whether drinking coffee breaks a fast. In this post, I share what we know from research as well as my personal test of coffee while fasting.
Black Coffee & Fasting – At A Glance
- An important activator of your metabolism clock is your first bite or sip of food or drink.
- Insulin sensitivity and fatty acid oxidation are most efficient at the start of your metabolic clock.
- Because the liver processes caffeine, coffee starts your metabolic clock.
- When put to the test, coffee on an empty stomach affected my ketone level and my husband’s blood glucose level.
- Coffee may start your metabolic clock, opening your eating window. However, it provides benefits with respect to autophagy and fat release.
Does Black Coffee Break a Fast? [Video]
In this video, you’ll learn…
- What intermittent fasting does to the body.
- Scientific studies on black coffee and intermittent fasting.
- My own personal tests with black coffee.
How Intermittent Fasting Works
One of the biggest advantages of intermittent fasting is that it allows you to work with your body’s natural metabolic rhythm by consuming food during the hours of the day when your metabolism is most active.
You can think of your metabolism as being a clock that runs well for a number of hours of the day and then winds down as the day ends. An important activator of your metabolism clock is your first bite or sip of food.
When your clock starts and your metabolic engine begins to rev up, your body experiences a peak in insulin sensitivity and fatty acid oxidation that gradually diminishes as the day goes on.
What that means is that your body is able to utilize and process food better at the beginning of your eating window than at the end.
Scientific Research on Black Coffee
Coffee & Your Metabolic Clock
Black coffee is a non-caloric drink. The question becomes: does black coffee count when it comes to starting your metabolic clock?
This is a gray area for sure, but there are a few hints we can take from the scientific literature. First of all, if your coffee contains caffeine, the caffeine would need to be processed by your liver, which is your main metabolic organ (1).
If you follow that wisdom alone, a person following a 16:8 style of intermittent fasting would start their eight-hour eating window with their first sip of caffeinated coffee.
If they start drinking coffee at 7 AM, their eating window would close at 3 PM.
However, many of the studies done on intermittent fasting allowed participants to consume non-caloric drinks like coffee and tea. The consumption of these drinks did not seem to hinder their results in a significant way.
Coffee Induces Autophagy
Another consideration is that there are helpful components in coffee that have been shown in mice studies to induce autophagy, which is a process of cellular clean up that is enhanced when we practice intermittent fasting (2)(3).
We know from studies with human participants that caffeine improves fat oxidation, which is the breakdown of fat (4).
There appears to be a tradeoff.
Your cup of black coffee might start your metabolism clock, which technically opens your eating window. But, if that is the only thing that you are consuming in the morning hours, you may be gaining an advantage with respect to autophagy and fat release.
My Personal Experience With Black Coffee
On my second YouTube Channel, my husband and I tested the effect coffee had on our bodies during a fast.
Specifically, we drank black coffee in a fasted state and then tested our blood glucose and ketones for the next two hours. [Watch the test here]
What we found was that coffee on an empty stomach raised my ketone level and lowered Keith’s glucose level. Both are favorable responses that indicate a movement toward improved fat burning.
Will Coffee Break a Fast?
The answer to the question, “does black coffee break a fast,” may be best answered by you.
- If you are a purist who likes to do things by the books, then I’d say you’ll be happiest if you do not drink black coffee during your fasting hours.
- If you are a coffee lover, who would feel lost without your morning brew, then you can likely enjoy it and may even gain some benefits from it.
(1) Sherman, Hadas, et al. “Caffeine alters circadian rhythms and expression of disease and metabolic markers.” The international journal of biochemistry & cell biology 43.5 (2011): 829-838.
(2) Sinha, Rohit A., et al. “Caffeine stimulates hepatic lipid metabolism by the autophagy‐lysosomal pathway in mice.” Hepatology 59.4 (2014): 1366-1380.
(3) Pietrocola, Federico, et al. “Coffee induces autophagy in vivo.” Cell Cycle 13.12 (2014): 1987-1994.
(4) Acheson, Kevin J., et al. “Caffeine and coffee: their influence on metabolic rate and substrate utilization in normal weight and obese individuals.” The American journal of clinical nutrition 33.5 (1980): 989-997.
About the Author:
Dr. Becky Gillaspy, DC graduated Summa Cum Laude with research honors from Palmer College of Chiropractic in 1991.