Coffee: Liquid Gold or Liquid Poison?

Updated: Aug 19, 2020

Coffee is the most valuable legally traded commodity, with the exception of oil.

While there are generally two biologically dissimilar species of coffee grown for consumption; Coffea canephora (Robusta) and Coffea arabica (Arabica), (1) there are actually 124 coffee species known to science. (2)

Arabica makes up for 60% of global coffee consumption. Whilst robusta is both less chemically complex and less flavoursome than arabica, it benefits from being feasibly grown at low altitude and is pest resistant.

In 2014, Brazil and Colombia combined to produce over 3.5 million tonnes of green arabica, with Ethiopia and other African and Central American producers also making significant contributions. Including countries like Vietnam, which almost exclusively produces robusta, global coffee production amounts to 8.5 million tonnes annually! (1)

Robusta is sometimes perceived negatively in terms of flavor, because it reminds some people of wood and tobacco. (2)

You’d think people shy away from drinking liquified wood and tobacco concoctions, but it is actually favored to add body to espresso and americano, and is even the species of choice for instant coffee. And it so happens that robusta is highly valued for its high caffeine content. (2)

After all is said and done, it's the caffeine that makes coffee popular. Sure, there are people that enjoy their daily fix in the form of decaf, but let’s face it, they are just a minority.

What effect does caffeine have on us?

In one study on caffeine they concluded caffeine improved endothelial function. (3) Endothelium is the inner lining of our arteries, that plays a pivotal role in regulating blood flow. (4)

They measured improved endothelial function by a standard test called brachial artery flow–mediated dilation. What that means is that they found that the main artery in the arm was able to dilate as a direct result from the caffeine. Arteries that can dilate are critical for improved blood flow.

Pretty amazing, right?

However, if we could measure the blood flow directly to the heart, or the myocardial blood flow, that would be even better, since the heart is the organ responsible for the distribution of blood flow after all.

Thankfully there is one such study. What did they conclude?

Caffeine IMPAIRS blood flow to our heart muscle after exercise, especially in people with heart disease (coronary artery disease). (5) That’s quite a different conclusion.

So how to interpret these findings?

Well, if you decide take a caffeine supplement, you may perhaps experience some benefits in blood flow. But if you decide to take them, don’t plan on taking them before any exercise, especially if you have heart problems.

That’s right, that’s all you can conclude, since coffee has little to do with this so far.

Harvard Health Publishing (HHP) analyzed that study on caffeine and improved endothelial function and came to the following conclusion: “The study does not make coffee into a health food. But it does add to the brewing evidence that tells us coffee is not toxic either.” (6) We will look in a minute if that conclusion holds up against other evidence. You can’t however, reach this conclusion based on this study alone. This is not to aimlessly take a dig at HHP, because they generally have solid articles. This is serves, however, as a good example to illustrate a point.

You see, to determine the effects of coffee on the human body, it would not suffice to just examine caffeine consumption alone. This is great if you want to know what effects caffeine has on the body, but that would not translate directly into any practical or accurate recommendations in respect to coffee. Did you know that coffee has over 1000 different compounds?! (7)

Why place so much emphasis on a single compound?

Caffeine constitutes only 0,01% of coffee’s total composition. (8)

This reductionist approach is not useful when the food or drinks we consume are a complete and often complicated ‘package’ we don’t even fully understand to begin with.

We need to measure the effect of coffee directly, to reach a more accurate and practical conclusion.

Scientists reached the conclusion that after drinking coffee, there was a significant drop of the arteries being able to dilate. (9), (10), (11)

They also measured the effects of decaffeinated coffee. Interestingly enough, decaf coffee seemed to improve dilation.

As you can see, the FMD (flow-mediated dilation) - the ability of the artery to dilate - improves on the decaffeinated coffee (D) and worsens on the caffeinated coffee (C).

The same can be found here. The FMD worsens on the caffeinated coffee.

Drinking decaf didn't cause any significant change though.

What’s going on here?

Since decaffeination of coffee removes more than just caffeine (12), perhaps there are other compounds involved that create this problem.

So it seems that there is a controversy about the health effects of coffee. This controversy wouldn’t be a controversy if we wouldn’t have opposite outcomes. And yes, other scientists measured improved endothelial function after the ingestion of coffee. (13)

We’ll briefly touch on this outcome in a minute.

There are actually hundreds of studies that have been done in relation to artery and heart health, as well as many other diseases, like cancer, liver health, Parkinsons, Alzheimer's, etc.

One of the biggest studies (meta-analyses) ever done on coffee, compiled the results of hundreds of studies and showed a lot of benefits, such as reduced risks in relation to different kinds of cancers, heart disease and decreased mortality. But most of this evidence comes from observational research that provides only low or very low quality evidence. And in regard to heart health, blood flow in the arteries wasn't measured. (14)

Coffee lovers, don’t get discouraged yet.

We are not done deciphering this mystery yet.

Coffee does seem to make a stronger case for having some liver protective effects. (15)

Also, in most studies they never accounted for caffeine metabolism.

Caffeine metabolism?

If you are a fast caffeine metabolizer, a stronger case seems to be made for 'supposed' coffee benefits. Among rapid caffeine metabolizers, daily coffee seems to have lowering effects on blood pressure and lower odds of getting a heart attack. Remember that coffee has over a 1000 different compounds? Among these are loads of antioxidants, which are likely responsible for the benefits. (16)

Maybe the reason why they found improved dilation of the artery in the earlier mentioned study, was because they used a high antioxidant coffee. (13) When we compare this high antioxidant coffee, with different coffees and their respective antioxidant content from other studies, it seems indeed that the antioxidant content, in the form of chlorogenic acid, is relatively high. (17), (18)

That could be one of the reasons a population in Ikaria, Greece, that drinks high antioxidant content coffee, appears to have improved endothelial function. (19) Although honestly, we probably can't contribute that to coffee alone because they consume a lot of whole plant foods, like greens and salads. (20) These foods also happen to form the bulk of the diet that has been shown to reverse heart disease by improving endothelial function dramatically. (21), (22)

When comparing different coffees and different brewing methods, we can clearly see differences in antioxidant content. There can even be more than a 10-fold difference in the antioxidant content. (23) Generally, espresso-based coffee tops the list, followed by brewed or filtered coffee. Most of the instant coffees are found at the bottom of the list.

The way coffee beans are roasted also impacts some of the antioxidants. The stronger the roast, the lower the antioxidant content. Coffees from popular coffee shops were put to the test and it appeared the regular Starbucks coffee didn’t even come close to the other competitors. Probably due to their dark roasts. (24)

Are you a fast or a slow caffeine metabolizer?

It may be more advantageous if you can metabolize caffeine at a faster rate.

If you are a slow metabolizer, you would perhaps benefit from a limited intake.

  • How to know if you are a fast or slow metabolizer?

  • How to know if your liver has enough of that enzyme responsible for metabolizing caffeine? (25)

You could undergo genetic testing, if you want to be absolutely positive.

Obviously, this won’t be on most people’s priority list.

But another effective way could be to see how you actually feel physically.


If you drink too much coffee, how long does it take before your body gets rid of the jitters?

If it takes hours, that might be a sign of a slower metabolism.

What does your blood pressure do after coffee consumption?

When your blood pressure increases after coffee consumption, that might be a sign of having a slow caffeine metabolism.

What does it do when you abstain from coffee for a few days?

If you haven't had coffee for a few days and your blood pressure drops, that might be a sign of a slow caffeine metabolism.

If you have a slow metabolism is there anything you can do?

Can you speed up your caffeine metabolism perhaps?

Well, in case you are not ready to part ways with coffee, it may be a good idea to reach out to broccoli and his close friends from the brassica family, like the different kinds of cabbages. (26), (27) They can actually increase the enzyme activity responsible for caffeine metabolism. That would be a double whammy, since these cruciferous vegetables have many other benefits as well, especially with the impact they have on cancer prevention. (28)

If you want to drink your coffee and want to minimise the potential harms and/or maximise the benefits, regardless if you are a fast or slow caffeine metabolizer, you would likely benefit from the following:

  • Choose a lighter roast coffee for increased antioxidant and chlorogenic acid content.

  • Avoid adding sugar

  • Avoid adding milk

  • Preferably no added sweeteners (sweeteners will be discussed in a future blog due to the complexity of the topic)

Why avoid sugar?

Sugar is not just empty calories. Its consumption is linked to an increase in non-communicable diseases such as heart disease, cancer and diabetes. (29)

The less sugar the better.

Why avoid milk?

In a test tube, even minuscule amounts of milk added to coffee have shown to reduce antioxidant activity. The addition of merely 17 ml (milliliters) reduced antioxidant activity by 62% and a 100 ml reduced it by a whopping 95%.

What about alternatives, like soy milk?

Soy milk also seems to reduce antioxidant activity. (30)

But these tests were done in a test tube, so how relevant is that?

What matters most is what we end up absorbing.

It appears that:

  • The bioavailability of chlorogenic acid drops significantly with the addition of milk;

  • The amount of chlorogenic acid found in the bloodstream of the black coffee drinkers is significantly higher. (31)

The amount of chlorogenic acid found in the blood stream of those who added soy milk to their coffee, was surprisingly not significantly different from those who drank their coffee black. Soy proteins initially bind the coffee compounds up in the small intestine, hence the lower activity measured in a test tube. After that, the good bacteria in the large intestine release them so they can be absorbed. (32)

Although we have come to the conclusion that the antioxidant content of coffee may be advantageous to at least some extent, the controversy doesn't quite end yet.

There are coffee compounds that can raise our cholesterol and have been associated with an increase in inflammation. (33)

Different brewing methods have different effects. You can read more about brewing methods here.



































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