Last week, LIFEApps featured a live AMA via our Facebook messenger chatbot with our chemist Zach Lawton and our science communicator Paige Jarreau all about coffee and intermittent fasting! In the span of two hours, we answered nearly 100 questions about how coffee impacts our health and the fasted metabolic state!

As a recap, we’ve included below a dozen of the most common questions we received during the AMA and our responses! As a bonus, we’ve included an intro from new LIFEApps blogger Joanna Filipowska, a postdoctoral fellow in the field of diabetes-related research at City of Hope!

Espresso. Photo by Janko Ferlic on Unsplash.
Espresso. Photo by Janko Ferlic on Unsplash.

On Coffee and Diabetes

By Joanna Filipowska

We often grab it on the way to work or drink it during our business and social meetings. Coffee, sweet or unsweetened, helps to keep our mind awake. But besides making our everyday life easier, coffee or rather caffeine and other substances that coffee contains, including phenolic compounds like chlorogenic acids (CGA), minerals and vitamins, can help regulate our metabolism. Coffee consumption can even impact our risk for chronic diseases like diabetes!

Moderate coffee consumption (meaning around 4 cups per day) is associated with a reduced risk of developing type 2 diabetes (Reis et al., 2018). The results of several studies suggest that coffee intake prevents cardiovascular mortality (Grosso et al., 2016) and has the potential to enhance weight loss (Santos & Lima, 2016).

Based on our current knowledge, it seems possible that compounds in coffee other than caffeine play the most relevant roles in regulating metabolic function long term. For example, the so called esters of caffeic acid, or caffeoylquinic acids (CQAs), present in coffee have been demonstrated to possess strong antioxidant properties (meaning they can suppress the negative process of cellular oxidation) and anti-adipogenic properties (they can prevent fat cell formation). They also regulate glucose absorption and suppress insulin resistance. Insulin is needed to regulate blood glucose levels; resistance to insulin causes blood glucose levels to increase, which is bad for us.

Coffee consumption also inhibits dangerous accumulation of fats (triglycerides) in the liver. Recently, Shokouh et al. (Shokouh et al.,, 2017) demonstrated that cafestol (a substance present in unfiltered coffee) improves insulin sensitivity in a rat model of metabolic syndrome. Cafestol also stimulates pancreatic beta-cells to secrete insulin and prevents high blood glucose by stimulating its uptake in skeletal muscle cells when tested in the laboratory conditions (Melbye et al., 2015), and it improves glucose control when administered in vivo (in living organisms, in this case, mice) (Melbye et al., 2017).

Cafestol is highest in unfiltered coffees including French press coffee, boiled Scandinavian brew and espresso. People at risk of high lipid levels may want to ask their physicians about drinking unfiltered coffee such as espresso, as cafestol may raise cholesterol levels. Overall, however, coffee consumption by humans is not associated with increased risk of heart disease but rather appears to protect the liver and to improve blood sugar control long term.

These findings overall suggest that different components present in coffee (both caffeinated and decaffeinated) can effectively protect us against diabetes, but also other types of diseases.

Conclusion?  If you are not a coffee lover yet, it is the right moment to become one!

Coffee beans. Photo by Jo Lanta on Unsplash.
Coffee beans. Photo by Jo Lanta on Unsplash.

Coffee AMA!

Does coffee break a fast?

When consumed in moderation, black coffee should not break your fast. In other words, having some coffee shouldn’t kick you out of ketosis or a fat burning state.

Caffeine in coffee CAN temporarily raise levels of stress hormones like epinephrine, which in turn can raise your blood glucose levels by signaling your liver to create new glucose molecules and blocking glucose uptake into your muscles. But some studies have shown that this only happens when coffee dosage reaches very high levels (13+ cups per day!)

With a moderate amount of coffee intake, especially if this coffee doesn’t have much caffeine (try darker roasts), you won’t have to worry about coffee breaking your fast.

Learn more here.

Does coffee stop autophagy?

It is true that a large amount of caffeine may stimulate insulin signaling and mTOR, the autophagy “brake” pedal. However, coffee actually tends overall to kickstart autophagy, due to polyphenols or plant compounds in coffee that can activate AMPK!

Learn more here.

How much coffee can I drink per day without breaking my fast?

You can generally drink up to 5 cups of coffee per 24 hours without having a significant impact on your fasting glucose levels. 1-2 cups shouldn’t activate mTOR or reduce your ketone production, as long as you don’t have diabetes or genetically slow coffee metabolism.

Learn more here.

Can I drink flavored coffee?

Yes, flavored coffee (or coffee that has been flavored in the brewing process) is a great way to cut your “sweet tooth” and pick up your energy levels while fasting without substantial calories and sugar. If ordering flavored coffee at a coffee house, however, make sure that the coffee has been roasted with flavor but not sweetened with sugared syrups after brewing.

You can also add cinnamon, vanilla powder and unsweetened cocoa powder to your coffee for taste without adding substantial calories that could break your fast.

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 bit 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 for 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.

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 to be added), 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!

Will bulletproof coffee break my fast?

Some people can drink bulletproof coffee without ending a fast, while for others it has similar impacts as eating a meal. It depends on how many calories-worth of butter you put in your coffee. You can have up to 500 calories per day during a multi-day fast or alternate day fasting. However, having all of that in one cup of coffee could impact your ketone production and insulin signaling.

You can monitor your ketones to see if bulletproof coffee has significant impacts your fast or kicks you out of ketosis.

Can I drink coffee if I have pre-diabetes?

Consumption of either caffeinated or decaffeinated coffee is actually associated with a lowered risk of type 2 diabetes! Learn more here.

However, if you currently have been diagnosed with diabetes, you should speak to your physician about drinking coffee while fasting or otherwise, as caffeine may impact your blood sugar responses to food.

Will coffee raise my blood sugar?

Caffeine in coffee may slightly and temporarily raise your blood sugar levels while fasting by raising levels of stress hormones like epinephrine. However, this typically requires very large doses of coffee (More than 10 cups per day).

You may not want to drink coffee while at the same time breaking your fast with a high-carb meal, as this could lead to harmful blood sugar spikes, especially if you have diabetes. However, you would probably have to drink several cups of coffee in a very short amount of time, in a matter of minutes, to experience this effect. With a moderate amount of coffee intake, especially if this coffee doesn’t have much caffeine (try darker roasts), you probably won’t have to worry about coffee worsening your glycemic response to food.

Speak to your physician if you do notice symptoms of hyperglycemia or hypoglycemia when you drink coffee while fasting or otherwise.

When is the best time to drink coffee during a fast?

We aren’t aware of any human studies that have investigated the impacts of coffee on fasting. For this reason, we don’t have any scientific rationale for the best timing of coffee intake during a fast.

However, there is evidence that caffeine in coffee can shift the central circadian clock (your body’s biological clock) to later in the day by about 45 minutes, according to circadian biology researcher Dr. Satchin Panda and fasting researcher Dr. Courtney Peterson. You probably want to avoid drinking coffee steadily throughout your fasting window if you are fasting most of the day. This could cause a form of ‘jetlag’ that could disrupt your sleep. Learn more here.

So the best rule of thumb is to enjoy only a moderate amount of coffee in the morning while fasting.

You can enjoy a "dry" or foamy cappuccino while fasting, if you need a few fasting-day calories. Photo by Toa Heftiba on Unsplash.
You can enjoy a “dry” or foamy cappuccino while fasting, if you need a few fasting-day calories. Photo by Toa Heftiba on Unsplash.

Can coffee impact my immune system?

Caffeine in coffee can activate PKA (protein kinase A), which has impacts on cell survival but also inhibits activity of some immune cells. This can be good in the case of inflammatory diseases; coffee intake has been associated with lowered levels of inflammation and immune cell activation. However, coffee’s activation of PKA could possibly suppress new immune cell growth seen to happen in prolonged fasting. This would likely require sustained, large doses of coffee or caffeine throughout a fast.

If you are worried about the impact of coffee on your immune system while fasting or otherwise, you may want to stick to coffee with lower caffeine content (such as darker roasts) or decaffeinated coffee. Learn more here.

Is it ok to drink coffee when breaking a fast?

It’s fine to enjoy some coffee as you break a fast, either in the form of a bulletproof coffee for example, or coffee with a meal. However, especially if you have diabetes or pre-diabetes, you may want to avoid large amounts of caffeine intake along with a high-carb meal. Caffeine can exacerbate blood sugar spikes.

Learn more here.

Does decaffeinated coffee have a different effect than caffeinated coffee, on the fasted state?

Caffeine has been shown to have benefits in terms of jump-starting the autophagy process, but so have other compounds in both caffeinated and decaffeinated coffee known as polyphenols.

Read more about the differences of caffeine and decaffeinated coffee in activating autophagy here.

If you are concerned about the impacts of large amounts of caffeine on your immune system, bone integrity or glucose and insulin levels, drinking decaffeinated coffee still rich in polyphenols is a good choice.

Can I drink coffee sweetened with an artificial sweetener while fasting?

Artificial sweetener can actually impact your gut microbes in negative ways and cause insulin resistance over time. It’s best to avoid if possible! Try some unsweetened cream in your coffee instead.

What else can I drink while fasting?

You can drink anything that doesn’t have calories! Ideally, also avoid beverages sweetened with artificial sweeteners, as these can impact your metabolism through your gut microbes.

For example, you can drink things like black coffee, unsweetened hot and cold teas, water with added electrolytes, carbonated water, water with lemon, etc.

If you are feeling like you need a little pick-me-up during a longer fast, you can enjoy some kombucha tea or other beverages with very small amounts of natural flavorings or plant fats added. For example, you might enjoy some coffee with a bit of butter or coconut oil added.


Paige Jarreau

I am the Director of Social Media and 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 offer disruptive solutions to healthcare providers, researchers, health IT companies and patients.

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