Coffee makes you smarter: here’s what happens to your brain without caffeine
Decaf coffee also affects the brain — and it’s not a placebo effect. A new study has shown for the first time in detail how regular and decaffeinated coffee alter the gut microbiome, and through it — mood, stress, and cognitive abilities. This connection doesn’t appear coincidental: scientists have previously shown that the gut influences the brain and memory. It turns out that caffeine is far from responsible for all the benefits we typically attribute to our morning cup of coffee.
The Effect of Coffee on the Gut and Brain
Scientists from APC Microbiome Ireland at University College Cork (Ireland) conducted a clinical trial involving 62 adults aged 30 to 50. Thirty-one of them regularly drank coffee (3 to 5 cups per day — considered moderate consumption by the standards of the European Food Safety Authority), while 31 participants did not consume coffee at all.
First, the researchers compared both groups on key indicators: body mass index, blood pressure, stress levels, anxiety, sleep quality, and physical activity. At baseline, no differences between the groups were found.
Coffee has been proven to have many beneficial properties.
Then the most interesting phase began. All coffee drinkers completely gave up coffee for two weeks — and during that time, researchers recorded significant changes in the metabolite profile of the gut microbiome. This aligns well with earlier data showing that coffee improves gut microflora. After the abstinence period, participants were given coffee again, but in a blinded fashion: half received regular caffeinated coffee, and half received decaf. No one knew which type of coffee they were drinking.
Decaf Coffee Improves Memory and Learning
The results were unexpected. Noticeable improvement in learning and memory was observed only in those who drank decaf coffee — this indicates that other coffee components, such as polyphenols, are responsible for the cognitive effects. That’s why it’s important to remember that coffee does more than just energize — it affects the body in much more complex ways.
At the same time, both types of coffee — caffeinated and decaf — showed common positive effects. Participants in both groups reported reduced perceived stress, depression, and impulsivity, as well as improved mood and cognitive performance.
Moreover, decaffeinated coffee additionally improved sleep quality and physical activity indicators. This makes sense: caffeine, as is well known, can interfere with falling asleep and alter sleep quality. But few expected that without it, coffee would retain (and even expand) its range of beneficial properties.
The Effect of Caffeine on the Brain, Anxiety, and Attention
Only caffeinated coffee was associated with reduced anxiety, improved alertness, and attention. Caffeine was also associated with a reduced risk of inflammation. Other experiments have shown that caffeine affects memory after sleep deprivation.
However, there’s a flip side. Among regular coffee drinkers, researchers recorded higher impulsivity and emotional reactivity compared to those who don’t drink coffee. Simply put, caffeine helps you focus but can make you a bit more “jittery” emotionally.
So we end up with a kind of menu of effects:
- Both types of coffee: reduced stress, depression, impulsivity; improved mood
- Caffeinated coffee only: reduced anxiety, improved attention, anti-inflammatory effect
- Decaf only: improved memory, sleep, and physical activity
Regular coffee and decaf affect the brain and gut differently
The Gut-Brain Connection in Coffee Consumption
Here it’s important to explain one key concept.
The gut and brain are connected through the so-called “microbiota–gut–brain axis.” This is why bacteria can influence not only digestion but also mood, appetite, and even cravings for sweets. It is a bidirectional biochemical link between the gastrointestinal tract and the central nervous system. Bacteria in the gut produce substances — neurotransmitters, short-chain fatty acids, metabolites — that influence brain function through the bloodstream, the immune system, and the vagus nerve.
This is precisely the mechanism the Irish scientists studied. They investigated coffee’s effect on the “microbiota–gut–brain” axis and assessed whether these effects manifest independently of caffeine in healthy participants.
It turned out that after resuming coffee consumption — both regular and decaffeinated — participants experienced characteristic shifts in microbiome composition. Certain bacterial strains were sensitive specifically to coffee as such, rather than to the caffeine in it.
Microbiologist John Cryan, the lead researcher, explains: coffee is not just caffeine, but a complex dietary factor that interacts with gut microbes, metabolism, and even emotional state.
Why Conclusions About Coffee and the Brain Are Not Yet Final
Before rushing to brew your fifth cup, there are several important caveats to consider.
The study sample is small — only 62 people, which may not reflect the diversity of microbiome profiles across different populations. Additionally, data on participants’ mood and behavior are based on self-reports, which are prone to memory errors and subjective biases.
The study also did not strictly control for other dietary variables — for example, added sugar and milk, which can independently affect gut health.
Another point worth knowing: the study was sponsored by the Institute for Scientific Information on Coffee (ISIC) — an organization that includes five major European coffee companies: illycaffè, JDE Peet’s, Lavazza, Paulig, and Tchibo. This doesn’t mean the data is unreliable — the work was published in the peer-reviewed journal Nature Communications and underwent independent review. But the source of funding is important to consider when evaluating any research.
Even decaf, according to scientists, can positively affect brain function
The study was conducted exclusively with instant coffee. As Professor Cryan noted, different types of coffee and preparation methods can significantly affect the chemical composition of the beverage — the brewing method changes the levels of caffeine, polyphenols, and other bioactive compounds.
Should You Drink Coffee Every Day for Brain Health and Memory?
The main takeaway from this work is not “drink more coffee,” but something more nuanced. Coffee affects the body in much more complex ways than we’re accustomed to thinking. Caffeine is just one of many active substances. Polyphenols, phenolic acids, melanoidins, and other compounds formed during roasting also play a role — and they work through gut bacteria.
According to the authors, the observed benefits of coffee are likely due to a combination of factors: biological effects of coffee compounds, microbiome-mediated mechanisms, and psychological effects related to habit and expectation.
For those who are sensitive to caffeine but love coffee, this is particularly interesting news. Decaf is not just “coffee for wimps.” Based on these findings, it retains a significant portion of beneficial properties and may even outperform regular coffee in certain aspects — such as memory and sleep.
