Coffee is many things

I recently wrote an article for The Conversation about seven of the weirdest things coffee does to your body.

It covered some of coffee’s less obvious or common effects: making some people need to poo, influencing reflux, interacting with medicines and iron absorption, affecting cholesterol, potentially feeding our gut microbes, and even getting parts of our digestive system ready for food.

The article got a lot of attention, which was lovely (it was even translated into Portuguese!) and it’s given me lots of reflections about how we talk and think about coffee. So here’s a listicle about that listicle.

2.We tend to reduce coffee to caffeine.

A lot of the discussion about the effects I described came back to caffeine: Is caffeine causing this? How much caffeine was in the coffee? Would an energy drink do the same thing? Sometimes caffeine is part of the answer. But coffee isn’t caffeine dissolved in brown water.

2. Coffee is a plant extract

Coffee comes from plants. We roast it, grind it, add water and extract a remarkably complicated mixture of chemicals from it. The experience of drinking coffee isn’t the same as popping a No-doze pill.

Caffeine is one part of the coffee extract, but it also contains chlorogenic acids and other polyphenols, trigonelline, diterpenes such as cafestol and kahweol, and compounds produced or transformed during roasting, including melanoidins. Researchers have described more than 1,000 bioactive compounds in roasted coffee.

And they don’t all do the same thing.

Some may interact with our gut microbes. Some affect digestion. Some influence lipid metabolism. Some can bind or interact with nutrients or medicines. Some are absorbed and metabolised; others travel further through the gastrointestinal tract.

Which is why one of my favourite clues in coffee research is when decaffeinated coffee produces an effect too. If removing most of the caffeine doesn’t remove an effect, something else in that complicated cup deserves our attention.

Tea is similar. We often talk about “the caffeine in tea”, but tea is another complex plant infusion containing polyphenols, amino acids such as L-theanine, caffeine and many other compounds. And processing changes that chemistry too: green and black tea start with the same plant, Camellia sinensis, but contain different profiles of bioactive compounds because of what happens after the leaves are picked.

Food is chemistry. But importantly, foods are mixtures of chemistry.

3. What happens when we zoom out from individual compounds?

There is another interesting part of the coffee story. Instead of asking what one molecule does over the next few hours, we can ask what happens to people who habitually drink coffee over years.

And, overall, the epidemiology of coffee is surprisingly reassuring. Large reviews have found that coffee consumption is more often associated with favourable than unfavourable health outcomes. Associations have been reported with lower all-cause and cardiovascular mortality and lower risks of conditions including type 2 diabetes and several liver diseases. In a large umbrella review, many of the strongest associations were around three to four cups per day.

That does not mean drinking three or four coffees a day is a prescription for good health. Because, with observational data, we need to acknowledge that people who drink coffee differ from people who don't in all sorts of ways, and although researchers try to account for those differences, observational studies cannot neatly prove that coffee itself caused the outcome. I can’t imagine anyone agreeing to be randomised into the coffee or non-coffee groups for long enough for us to study this with an RCT!

There are also circumstances where caffeine intake matters, including pregnancy, and individual responses to coffee vary enormously. But the overall pattern is important because it gives us context (but we need to acknowledge no human is the average!)

If we looked only at isolated mechanisms, caffeine raising alertness, coffee temporarily affecting blood pressure, compounds interfering with iron absorption, or diterpenes affecting cholesterol, it would be very easy to construct a story in which coffee sounds terrible for us.

Zoom out to whole humans living whole lives, and that isn't the pattern we see. Nutrition science needs both views.

4. There isn't really one thing called “coffee”

There is another complication hiding inside all of this.

When a study says someone drinks “three cups of coffee a day”, what exactly does that mean?

An espresso is not chemically identical to instant coffee. Neither is a paper-filtered coffee, French press, cold brew, moka pot or Turkish coffee.

The bean matters. The roast matters. The grind matters. The ratio of coffee to water matters. The temperature and extraction time matter.

And importantly, the brewing method changes what ends up in the cup.

One good example is the diterpenes cafestol and kahweol. Paper filtration removes much more of these compounds than brewing methods where the coffee remains unfiltered. This matters because coffee diterpenes can raise blood cholesterol. It isn't just a theoretical difference. A large Norwegian cohort study following more than 500,000 people for around 20 years found different mortality patterns according to whether people predominantly drank filtered or unfiltered coffee.

And then there’s the differences in individual plants, and the production methods…

6.The Biases!

Everyone who already drinks and loves coffee wants to be convinced that’s the rght choice. Everyone who already thinks they react poorly to coffee wants the down low on how they are correct. Coffee isn’t essential (even though it feels like it for some of us!) so we don’t really need to argue about it. But writing about coffee has been a lovely reminder that coffee is a real social and culture experience too. Remember though - if someone invites you for a coffee they actually mean they would like to hang out with you and you can drink anything you like!

7.The bottom line

Foods aren't simply vehicles carrying one nutrient or bioactive compound into our bodies. They are complex physical and chemical mixtures, shaped by the plant or animal they came from, how they were processed, how we prepared them and what we consumed them with.

Our bodies are complicated too.

Which is why nutrition gets much more interesting when we stop asking only “what does this one compound do?” and start asking “what does this whole food, in this form, in this person, in this dietary pattern, actually do?”

And coffee is a particularly delicious example.

You can read my original The Conversation article, “7 of the weirdest things coffee does to your body”, here.

 3.4