Paige Jarreau, PhD
Paige is the VP of Science Communication for LifeOmic and an avid blogger. She’s interested in how scientists use social media to promote public engagement and health behaviors.

Paige Jarreau, PhD
Paige is the VP of Science Communication for LifeOmic and an avid blogger. She’s interested in how scientists use social media to promote public engagement and health behaviors.


Can you drink coffee while fasting? This is one of the questions we get most frequently from our readers and LIFE Fasting Tracker users. The simplest answer is yes. In fact, coffee may boost many of the physiological impacts of fasting.

But because we are into exploring, tracking and measuring the impacts of intermittent fasting on our health, let’s dive deeper into this story of coffee and fasting.

What you’ll find in this article:

 Coffee and fasting FAQ

How coffee impacts your fast

Takeaways

 

Will coffee break your fast? Probably not! You can even enjoy a tad of cream or butter in your coffee while fasting, but avoid sugar. Image Credit: Elle Hughes.
Can you drink coffee while fasting? Yes! You can even enjoy a tad of cream or butter in your coffee while fasting, but avoid sugar. Image Credit: Elle Hughes.

Can you drink coffee while fasting? The short answer is yes

You can drink coffee in moderation (up to 3-5 cups/day) while you are fasting. In other words, having some coffee won’t kick you out of ketosis or a fat burning state. This is usually true as long as you are a healthy individual who hasn’t been diagnosed with diabetes and who metabolizes coffee quickly (there are gene variants that cause slow clearance of coffee from the body).  

Can I drink flavored coffee?

Yes, flavored coffee is a great way to pick up your energy levels while fasting without substantial calories or sugar. Make sure you are buying coffee that has been roasted with flavor but not sweetened with sugared syrups after brewing. 

Can I have cream and sugar in my coffee while fasting?

To stay in a fasted metabolic state, it’s best not to add any cream or sugar to your coffee. However, if you’ve already fasted overnight for 12 or so hours and you just can’t drink black coffee, a splash of cream, butter, coconut oil, MCT oil or other healthy plant fat likely isn’t going to kick you out of ketosis or a fat-burning state.

At most, these coffee fixings might lengthen the time it takes you to get into ketosis after an overnight fast. They can slightly and temporarily activate your insulin and mTOR pathways, telling your body that nutrients are around and thus delay entry into autophagy (cellular recycling). However, it’s normal in human clinical studies of fasting to allow participants up to 500 calories on fasting days; fasting benefits occur regardless of these few calories.

Sugar is another beast, as it can quickly raise your blood sugar levels. Try to avoid adding sugar into your coffee, opting for cream or other healthy fats instead. Also watch out for sugar-added creamers.

Will bulletproof coffee break my fast?

Bulletproof coffee (coffee + butter and MCT oil ) is satisfying and it helps you avoid hunger while you’re fasting.  If you are just getting used to intermittent fasting, bulletproof coffee can help you reach your fasting goal more comfortably.  Bulletproof coffee should’t interfere with the weight loss benefits of intermittent fasting.  If you are not getting the results you want, switch to regular black coffee.

What else can I put in my coffee that won’t break my fast?

You can add spices such as cinnamon or nutmeg, vanilla powder or unsweetened cocoa powder. You can also add a splash of almond milk or 1 teaspoon of coconut oil. Always stay away from sugar and avoid artificial sweeteners. The latter increase cravings for some people.

What drinks can I order from Starbucks that won’t break my fast?

Starbucks’ coffees that won’t break a fast include their regular drip coffees without any cream or sugar added. While fasting you could also order an Americano (expresso and water), cold brew or iced black coffee (ask for no syrup or sugar), and black or green iced or shaken tea (ask for no sweetener). You could also have a small cappuccino during a longer fast, but you’ll want to ask for foam only or just a splash of milk!

What else can I drink during a fast besides coffee?

You can drink water, sparkling water or naturally-flavored water with a lemon slice,  a leaf of mint or thyme. You can also drink tea, just don’t add any sugar or honey.

Coffee can impact your fast in other ways

Can you drink coffee while fasting? Coffee does not raise blood sugar in healthy people

Caffeine can temporarily raise levels of stress hormones like cortisol and epinephrine. These can in turn raise your blood glucose levels by signaling your liver to create new glucose molecules from proteins and fatty acids. Stress hormones can also temporarily block glucose uptake into your muscles (although exercise can help). Dose matters for these effects. Consuming two cups of black coffee in 10 minutes may double levels of plasma epinephrine. However, epinephrine infusions in humans that cause plasma levels to reach 3-5 times normal levels  cause only small changes in fasting blood glucose levels (~5 mg/dl).

Overall, moderate coffee intake is unlikely to raise your fasting blood sugar levels enough to dampen or delay ketone body production or ketosis. You won’t have to worry about black coffee breaking your fast, especially if you isolate your consumption to the morning and don’t drink coffee continuously throughout your fast.

“The degree to which moderate or typical caffeine consumption impacts circulating glucose or insulin response is minimal in healthy people,” says Dr. Imogen R. Coe, founding dean of the Faculty of Science at Ryerson University and a researcher who studies nucleoside transporters. “In fact, caffeine consumption may be correlated with better glucose responses in healthy people to some extent.”

Can you drink coffee while fasting? Coffee might be a concern if you have diabetes or prediabetes

The bigger concern is for individuals with diabetes or prediabetes consuming large amounts of caffeine during high carbohydrate meals. In this case, the blocking effect of caffeine on glucose uptake can cause heightened hyperglycemia (high blood sugar).

“… large amounts of caffeine with meals may exaggerate hyperglyemia in type 2 diabetes patients.” – Lane et al., 2012

Overall, you probably don’t have to worry about coffee significantly impacting your blood sugar levels as long as you are a healthy individual drinking moderate amounts of coffee (up to 5 cups per day). Polyphenols in coffee in particular may actually improve your glycemic responses to food over time, an effect that mimics intermittent fasting.

If you are concerned,  try drinking decaffeinated coffee or coffee that doesn’t have much caffeine (try darker roasts) while fasting. 

It’s ok to drink coffee during a fast! But talk to your doctor first if you have diabetes or prediabetes.

Can you drink coffee while fasting? Too much coffee may raise insulin levels

Coffee and caffeine have a somewhat complicated relationship with insulin in our bodies. Habitual moderate coffee drinking my increase insulin sensitivity and lower risk for type 2 diabetes. But in acute and high doses, caffeine can decrease insulin sensitivity and raise plasma insulin levels. This effect runs counter to the goal of intermittent fasting, which is to lower insulin levels.

The insulin-raising effect of caffeine is more likely to happen for individuals already at risk of developing diabetes, as well as individuals consuming higher doses of caffeine. For example, a series of randomized controlled trials in healthy individuals found that heavy coffee consumption (the equivalent of 13 conventional cups of coffee per day after several weeks of complete coffee abstinence!) significantly raised insulin levels. However, a more moderate intake of 5-8 cups of coffee or 870 mg of caffeine per day only slightly raised plasma insulin levels.

If you are worried about coffee raising your insulin levels, just drink in moderation! A few cups of black coffee in the morning should be fine.

Coffee may increase autophagy

Coffee has many different compounds in it, not just caffeine. Plant compounds in coffee may increase autophagy, a cellular recycling stage of intermittent fasting! 

Coffee has been shown in cell culture and animal model studies to enhance autophagy in liver, muscle and even brain cells!

A study showed that caffeine promotes autophagy in the skeletal muscle of rats.

Another study found that both natural and decaffeinated coffee increased autophagy in mice 1-4 hours after coffee consumption. There was higher autophagy in the liver, heart and muscles.

This increase in autophagy was accompanied by the inhibition of mTOR (which fasting also inhibits). Coffee consumption may also induce broad deacetylation of cellular proteins. Protein deacetylation, where molecules called acetyl groups are removed from lysine residues in proteins, is a change that also happens with caloric restriction or fasting in animal models. Deacetylation of key proteins turns on autophagy. It just so happens that antioxidant compounds found in decaffeinated coffee can also deacetylate key proteins to turn on autophagy.

This research suggests that compounds that are not removed in the decaffeination process, presumably polyphenols, may have an even stronger effect on autophagy activation.

This does not mean that coffee is required for maximizing autophagy. However, a little coffee early in your day may increase that valuable recycling time as you fast.

Coffee may reduce inflammation

Caffeine and other compounds in coffee including theophylline, a caffeine-like compound, can affect levels of cyclic AMP (cAMP) within cells. cAMP is an important messenger that can activate many other proteins, including protein kinase A (PKA). Coffee can raise levels of cAMP through the adenosine receptors, which activate cAMP, as well as by inhibiting phosphodiesterases (PDEs) that normally degrade cAMP.

By raising levels of cAMP, theophylline  dilates the airways and reduces inflammation in asthma patients. Caffeine has also been found to lower levels of proinflammatory cytokines including tumor necrosis factor TNF-α in human blood, through the cAMP/PKA pathway.

Coffee beans. Photo by Jo Lanta on Unsplash.
Coffee may increase autophagy and reduce inflammation. Photo by Jo Lanta on Unsplash.

Coffee is good for your brain 

Caffeine can activate some metabolic processes and signaling pathways, while blocking others. These effects may vary from individual to individual and also from tissue to tissue and cell type to cell type. This is partly because caffeine is a blocker of adenosine receptor activity. Adenosine receptors are found on cells throughout the human body. They play a role in cardiac rhythm and circulation, fat breakdown, renal blood flow, immune function, sleep regulation, formation of new blood vessels, inflammation and neurodegenerative disorders.

“It can be calculated that the daily consumption of three to four regular cups of coffee results in approximately 50% [adenosine] receptor occupancy for several hours.” – Adenosine Receptors as Drug Targets

By blocking these receptors, caffeine can at least temporarily have widespread effects throughout the body. Many of these effects are beneficial, such as protection of brain cells from death and injury, synaptic plasticity (growth of new brain cell connections), reduced inflammation, reduced insulin resistance, airway dilation and lowered activation of immune mast cells, which helps to reduce allergy and asthma-related symptoms.

However, some of the effects of adenosine receptor blocking by caffeine are less ideal in the context of fasting. By blocking adenosine receptors, caffeine can increase insulin secretion and reduce bone and immune stem cell growth and differentiation. Prolonged fasting and fasting mimicking diets may rejuvenate the immune system in animal models by activating immune stem cell renewal. Whether caffeine could interfere with these benefits of fasting is unknown. What we do know is that it would likely take large and sustained doses of caffeine throughout the fasting period to have such an effect.

Coffee may reduce Alzheimer’s risk

By raising levels of cAMP and blocking adenosine receptors, caffeine and other compounds in coffee can also activate PKA or protein kinase A. PKA is a family of enzymes that have many downstream impacts on the body and its metabolic functions. PKA helps to regulate glucose production and metabolism, lipid metabolism, contraction and relaxation of heart muscle, and even nerve cell activity and activation of the brain’s reward system.

As always, PKA can have both beneficial effects on the body as well as less beneficial ones in the context of intermittent fasting.

On the beneficial side, coffee-activated PKA signaling slows cognitive decline, increases working memory and reduces both the risk and symptoms of Alzheimer’s disease, among other neurodegenerative diseases. Just 1-3 cups of coffee per day can produce plasma concentrations of caffeine shown to prevent the formation of amyloid plaques in the brain of an animal model of Alzheimer’s disease. A dose of 4-6 cups of coffee per day (400-600 mg) has therapeutic potential for Alzheimer’s disease and reduces the risk of type 2 diabetes, Parkinson’s disease and liver cirrhosis. This level of coffee intake does not seem to have any adverse impacts on the heart. This may be due to the other antioxidant and anti-inflammatory plant compounds found in coffee.

Caffeine raises levels of cAMP and activates PKA, which in turn lowers the activity of the pro-inflammatory NFkB pathway. The NFkB pathway increases inflammation levels but also elevates levels of an enzyme that helps produce the amyloid beta protein that gums up brains affected by Alzheimer’s disease. Caffeine also suppresses the activity of GSK-3, an enzyme that helps produce the protein tangles of Alzheimer’s disease and has also been implicated in type 2 diabetes, inflammation, cancer and mood disorders. Finally, other plant compounds in coffee have antioxidant properties and can reduce the levels of inflammatory cytokines in the brain.

Coffee can delay sleep by impacting production of melatonin

Something all individuals practicing intermittent fasting should be aware of is that caffeine in coffee can reset our daily or circadian biological rhythms. Intermittent fasting also impacts our circadian rhythms, usually in a positive way if we eat in tune with our daylight and active hours and fast longer overnight. But drinking coffee, especially later in the day, can delay our circadian melatonin rhythms by 40 minutes or more depending on the dose. Cyclic AMP actually plays a role here too; the rising and lowering of cAMP levels helps our cells keep time, so to speak. By preventing the degradation of cAMP, caffeine lengthens the period of cellular circadian rhythms.

In other words, when exposed to caffeine our cells go through a kind of jetlag where their days get longer.

In summary, caffeine intake in the form of coffee can impact our circadian rhythms and lower our production of melatonin, the sleep hormone. It’s best for this reason to confine your coffee intake to early in the day, especially if improved sleep is one of the benefits you’d like to glean from your daily intermittent fasting practice.

Coffee and the gut microbiome

Coffee contains polyphenols, ring-shaped compounds that absorb ultraviolet and other light and protect the body against free radicals. There are many polyphenols in nature including catechins in wine, tea, apples, grapes, blueberries etc.; isoflavones found in soybeans; and chlorogenic acid found in coffee.

Coffee and its polyphenols can promote the growth of healthy gut microbes including Bifidobacterium, which may help prevent colorectal cancer and inflammatory bowel disease.  Coffee and its polyphenols also support the growth of  Akkermansia, which is associated with improved blood sugar control and weight.

Different people metabolize coffee differently

 Pregnant women, for example, metabolize coffee more slowly; it can take twice as long for caffeine to leave their systems as compared to before they were pregnant. Some people also have a genetic predisposition to metabolize coffee slowly. A 23andMe report can give you an indication of your ability to metabolize coffee quickly or slowly! (If you feel wired after a small amount of coffee, you may want to look into whether you have a CP1A2 coffee metabolism gene variant).

Takeaways- Can you drink coffee while fasting?

Congratulations, you’ve just learned a LOT in a small amount of time about the nitty gritty details of how coffee impacts the human body and metabolism!

We leave you with some takeaways below.

Keep your coffee intake moderate

Moderate coffee consumption (up to 3-5 conventional cups per day) is safe and shouldn’t break your fast. Drink coffee with less caffeine (darker roasts have less caffeine) if you are concerned about its impacts on your glucose and insulin levels. When you are fasting you can drink black coffee, flavored coffee, coffee with a splash of milk or sugar-free cream, or bulletproof coffee. Avoid sugar at all costs! Sugar raises your insulin which keeps you from losing weight.

Talk to your doctor about coffee if you have diabetes or prediabetes

 Ask your physician how caffeine may impact your blood sugar levels. Generally try to avoid large doses of coffee (several cups) in conjunction with high-carb meals.

There are other things you can drink during a fast besides coffee

These include water, sparkling water or naturally-flavored water with a lemon slice, or a leaf of mint or thyme. You can also drink tea, just don’t add any sugar or honey.

Coffee impacts your fast in other ways. For example, it may increase autophagy

Are you fasting for autophagy, mental clarity or to preserve cognitive function as you age? Coffee may actually boost the impacts of fasting in this area! Enjoy a few cups of ideally black coffee per day! It’s ok to put a little cream or butter in your coffee while fasting, but avoid sugar, sweetened creamer or artificial sweeteners, which can activate insulin signaling and mTOR.

Coffee may improve asthma symptoms

Do you suffer from asthma or chronic inflammation? Coffee may help improve your symptoms! Enjoy moderate coffee with your prolonged fasts.

Coffee interferes with your sleep

Do you have trouble sleeping or are you practicing time-restricted eating to improve your sleep? Go easy on the coffee and only drink it in the mornings.

Exercise and avoid overdoing coffee for bone health

Have you been diagnosed with osteoporosis or are you concerned about your risk? Especially if you are a postmenopausal woman with low estrogen levels, you may want to cut back on your caffeine intake to preserve bone density. Speak to your physician about this if you have concerns.

Doing a fast? Share your experiences with us on Instagram and Facebook  with the hashtags #SeizeLIFEFast #LIFEfastingapp.

Download the LIFE Fasting Tracker app here.

This post was updated by Luisa Torres, PhD.


Paige Jarreau, PhD

I am the VP of Science Communication for LifeOmic and an avid blogger. I'm interested in how scientists use social media to promote public engagement and health behaviors.

LifeOmic® is the software company that leverages the cloud, machine learning and mobile devices to improve healthspans – from prevention and wellness to disease management and treatment.

     

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